Continuously Variable Transmissions

Continuously Variable Transmissions, or CVT's, as they are called in the trade, are used in snowmobiles, some all terrain vehicles (ATV's), and a few automobiles. A continuously variable transmission works just like it sounds. It continuously varies the gear ratios between the engine and the final drive. There is no need to select different gears: just place the shifter in forward and away you go.

Why use a CVT rather than a conventional automatic or manual transmission? The answer is efficiency; engine efficiency. With a CVT, the engine goes from an idle to a pre-programmed rpm immediately so the engine input is constant, and the transmission varies the output speed for smooth, seamless acceleration. Keeping the engine at a constant rpm allows the engineers to optimise ignition timing, camshaft design, and manifold tuning for excellent volumetric efficiency and low emissions.

Other reasons for using CVT's include simplicity of design, and smooth power application to the ground. The simplicity part comes by using fewer parts. Vehicles with reverse gear obviously have more parts than a simple forward drive, but there are still fewer parts and gears to manufacture.

The smooth power application of CVT's is useful in off-road vehicles. Power can be applied without any jerks or surges that could cause the vehicle to lose traction on steep climbs or loose terrain.

So how do they work? The two most common systems use a belt or a chain. Let's look at snowmobiles first. They use a belt. On a snowmobile there are two pulleys connected by a rubber drive belt. Both pulleys are "V" shaped and the width of the "V" can be varied. The drive pulley is connected to the engine and the width of the pulley is controlled by engine speed. At idle, the pulley is wide and the belt is not gripped. Push on the throttle, and the governor causes the pulley sides to move together. When engine speed reaches it's maximum, the pulley continues to become narrower as vehicle speed increases, causing the drive belt to climb up and keeping the engine at its peak power.

The driven pulley also varies its width, but its main job is to keep the slack out of the belt. The driven pulley halves are spring loaded to force them together, and as the drive pulley closes up, the belt climbs up the drive pulley causing the belt to tighten, forcing the driven pulley apart. The variable width of the pulleys and the variable distance of the belt from the centre of the pulleys provide the continuously variable drive.

Automobiles with CVT's use a drive chain instead of a rubber belt. The chain is stronger and more durable on a much heavier vehicle. Although much more complex, automotive CVT's use variable width pulleys just like snowmobiles. Hydraulics and computer controls are used to vary the width of the drive pulley.

Lockers Explained

When you think of traction control on your Jeep, most likely the first thing that comes to your mind is the tires. While tires are an essential part of good traction off road, most of us don’t seem to remember that it’s the differential that controls just how much power our tires are going to receive. In most cases, an open differential makes it extremely hard to gain the necessary traction you need on the trail, no matter how awesome your tires. Now, how do we fix that problem? The answer: Lockers.
Lockers provide you with much more control over the power distribution to your tires, both on and off the road. The type of locker you install will determine the extent of control you have over the locker or whether or not the locker automatically engages itself. This article is meant to give you an idea of the most popular types of lockers available for your Jeep.

Let’s begin with a quick explanation of what lockers do. Simply put, a locker is a device that controls power distribution to your tires and control how power is redistributed to the tires in different situations, such as changing terrain and tire spin. Housed in the differential case, lockers come in two options, Selectable and Automatic. We’ll divide these into two sections for simplicity’s sake:

Selectable Lockers: These types of lockers allow the driver to control when the locker is engaged and when it disengages, hence the name “Selectable”. These lockers are controlled either pneumatically by an air compressor, or electronically by the use of magnetically charged currents.

Animation of ARB Air Locker courtesy of www.arbusa.com

Air-actuated Selectable Lockers: Air actuated lockers are usually controlled by a switch mounted on the dash. The switch controls an air solenoid that in turn sends pressurized air down a pneumatic air line to the axle housing and into the air locker in the differential. The compressed air actuates the piston and clutch gear, moving the gear into the “locked” position. The side gear is locked to the housing providing 100% traction lock-up between the two axle shafts.
The locker is deactivated by a flip of the switch, forcing the solenoid to release the air pressure. In turn the piston springs return to the pistons and the clutch gear returns to its original open position. The best example is an ARB Locker like the one in the animation to the right.

The benefits of Air Actuated Selectable Lockers:

100% traction on demand without driveline wear
Easy to install, operate, and maintain
Simple design with minimal moving parts, making it ultra-durable
No extra tire wear
Option to disengage in places that an automatic locker could not such as hill-sides or rocky areas where an open diff would perform much better than a locked one.

The disadvantages of Air Actuated Selectable Lockers:

High initial cost
Must have an air compressor
Require air hoses and fluid to work

Electronic Selectable Lockers:Electronic Lockers operate very similarly to their air counterparts, with the exception that instead of using compressed air they use electromagnetic pulses to engage and disengage the locker mechanism. These electronic signals are also controlled by a switch that the driver can easily control. An example would be an Eaton ELocker.

The benefits of Electronic Selectable Lockers:

No compressor noise
100% traction on demand without driveline wear
Easy to install, operate, and maintain
No extra tire wear
Can disengage in places that automatic lockers would self-engage, such as hill-sides or rocky areas where an open differential would perform much better than a locked one.

The disadvantages of Electronic Selectable Lockers:

High initial cost
More moving parts
Requires electricity to operate

Oxlocker: Functions the same as an Electronic locker, except using cabling to control the locking mechanism instead of electronics.

The benefits of an Oxlocker:

Does not require electricity or air to operate
Less costly

The Disadvantages of an Oxlocker:

Cheaper material
Cable malfunctioning, or getting caught on something

Automatic Lockers: This type of locking system is not user controlled; rather, it is controlled by certain conditions such as speed, torque, and tire spin. There are several different types of automatic lockers, which vary in cost and usability.

Torque Actuated: A torque actuated locker is automatically controlled by the amount of twisting force exerted on the differential. This type of automatic locker is essentially always engaged, as the driver has no direct control over the components. The locker can sense turns and it will disengage itself when going around corners, as long as you aren’t giving it gas, allowing the wheels to spin at different speeds to properly turn the vehicle. Examples include Eaton’s Detroit series Locking Differentials.

Gleason-Torsen: Similar to a Detroit Trutrac. Was more popular 15-20 years ago but they aren’t seen anymore.

The benefits of Torque Actuated Automatic Lockers:

Never have to worry about when to engage your locker.
No extra components such as switches or air lines are required.
This is the only automatic locker that can work when one tire is completely off the ground.

The disadvantages of Torque Actuated Automatic Lockers:

Almost always engaged
No way to control, completely automated
Increased tire wear

Limited Slip: Limited slip lockers are a good bridge between your standard differential and a full locking diff. These lockers are not capable of 100% full lockup; however they provide a lot better traction when off-roading than an open carrier.

The benefits of a Limited Slip Automatic Locker:

More cost-efficient to manufacture
Never have to worry about engaging it
More forgiving on the street than a Torque Actuated Locker

The disadvantages of a Limited Slip Automatic Locker:

Do not provide 100% lock-up
Requires special oil friction modifier

Spools: Spools are the simplest way to lock your differential. Simply put, a spool is a solid carrier that allows for no wheel speed differentiation. Spools are always engaged. This type of locker is usually seen in competition and drag racing.

The benefits of Spools:

Extremely cheap
Permanently locked
Allows no change in wheel speed differentiation

The disadvantages of Spools:

Tire wear
Low turning radius
Additional stress applied to shafts

Mini-spools: Mini spools replace the spider gears in an open differential into a full non-differentiating diff that locks both shafts together. This would make it just as strong as the stock carrier is.

The benefits of a Mini-Spool:

Most cost-effecient locker available
Can use the same stock carrier

The disadvantages of a Mini-Spool:

Like all other automatic lockers, cannot control when engaged
Prone to break

Inside Bruce Crower’s Six-Stroke Engine

Inside Bruce Crower’s Six-Stroke Engine

Bruce Crower has lived, breathed and built hot engines his whole life. Now he’s working on a cool one—one that harnesses normally-wasted heat energy by creating steam inside the combustion chamber, and using it to boost the engine’s power output and also to control its temperature.

“I’ve been trying to think how to capture radiator losses for over 30 years,” explains the veteran camshaft grinder and race engine builder. “One morning about 18 months ago I woke up, like from a dream, and I knew immediately that I had the answer.”

Hurrying to his comprehensively-equipped home workshop in the rural hills outside San Diego, he began drawing and machining parts, and installing them in a highly modified, single-cylinder industrial powerplant, a 12-hp diesel he converted to use gasoline. He bolted that to a test frame, poured equal amounts of fuel and water into twin tanks, and pulled the starter-rope.

“My first reaction was, ‘Gulp! It runs!’” the 75-year-old inventor remembers. “And then this ‘snow’ started falling on me. I thought, ‘What hath God wrought…’”

The “snow” was flakes of white paint blasted from the ceiling by the powerful pulses of exhaust gas and steam emitted from the open exhaust stack, which pointed straight up.

Over the following year Crower undertook a methodical development program, in particular trying out numerous variations in camshaft profiles and timing as he narrowed the operating parameters of his patented six-stroke cycle.

Recently he’s been trying variations of the double-lobe exhaust cams to delay and even eliminate the opening of the exhaust valve after the first power stroke, to “recompress” the combustion gasses and thus increase the force of the steam-stroke.

The engine has yet to operate against a load on a dyno, but his testing to date encourages Crower to expect that once he gets hard numbers, the engine will show normal levels of power on substantially less fuel, and without overheating.

“It’ll run for an hour and you can literally put your hand on it. It’s warm, yeah, but it’s not scorching hot. Any conventional engine running without a water jacket or fins, you couldn’t do that.”

Indeed, the test unit has no external cooling system—no water jacket, no water pump, no radiator; nothing. It does retain fins because it came with them, but Crower indicates the engine would be more efficient if he took the trouble to grind them off. He has discarded the original cooling fan.

So far he has used only gasoline, but Bruce believes a diesel-fueled test engine he is now constructing—with a hand-made billet head incorporating the one-third-speed camshaft—will realize the true potential of his concept.


Potential…and Questions

Crower invites us to imagine a car or truck (he speaks of a Bonneville streamliner, too) free of a radiator and its associated air ducting, fan, plumbing, coolant weight, etc.

“Especially an 18-wheeler, they’ve got that massive radiator that weighs 800, 1000 pounds. Not necessary,” he asserts. “In those big trucks, they look at payload as their bread and butter. If you get 1000 lb. or more off the truck…”

Offsetting that, of course, would be the need to carry large quantities of water, and water is heavier than gasoline or diesel oil. Preliminary estimates suggest a Crower cycle engine will use roughly as many gallons of water as fuel.

And Crower feels the water should be distilled, to prevent deposits inside the system, so a supply infrastructure will have to be created. (He uses rainwater in his testing.) Keeping the water from freezing will be another challenge.

But the inventor sees overriding benefits. “Can you imagine how much fuel goes into radiator losses every day in America? A good spark-ignition engine is about 24 percent efficient; ie., about 24 cents of your gasoline dollar ends up in power. The rest goes out in heat loss through the exhaust or radiator, and in driving the water pump and the fan and other friction losses.

“A good diesel is about 30 percent efficient, a good turbo diesel about 33 percent. But you still have radiators and heavy components, and fan losses are extremely high on a big diesel truck.”

Bottom-line, Bruce estimates his new operating cycle could improve a typical engine’s fuel consumption by 40 percent. He also anticipates that exhaust emissions may be greatly reduced. It’s all thanks to the steam.

“A lot of people don’t know that water expands 1600 times when it goes from liquid into steam. Sixteen hundred! This is why steam power is so good. But it’s dangerous…”

The danger of a boiler explosion has long been a factor in engineering—and in operating—steam powerplants of all kinds, and Crower is properly wary of the miniature boiler he has conjured up inside his test engine. That’s one reason he chose to use one originally manufactured as a diesel, for its inherent strength, though he installed a carburetor and ignition system so it could burn gasoline at first.

The original diesel fuel injector system now supplies the water spray to generate the steam-stroke.

In addition to producing extra power, the injected water cools the piston and exhaust valve, which suggests to Crower that he could raise the compression ratio. “I’ve done this many times on regular engines: 15-to-1 on gasoline for the first five seconds works pretty good until you get some chamber heat and then suddenly it gets into pinging. But with the chamber being chilled, I bet 12-, 13-to-1 will be no problem on cheap fuel.

“So what we can maybe do is have fuels that aren’t quite as good…It’ll save a nickel a gallon not having to keep three grades going.”

As for his hope of lowering emissions, Bruce speculates the steam might purge “cling-on hydrocarbons” out of the combustion chamber. “This thing may turn out to be so clean that you won’t have to have a catalytic converter.

But he admits that’s unknown, saying “there’s a lot of experimenting still to be done.” Which prospect makes him smile. He thrives on this kind of challenge.


Bruce’s Background

“You’ve kinda got to be in the cam business and know the dynamics of engines,” Bruce Crower says about how the idea occurred to him. And he certainly has that background.

He was building and racing hot rods (and hot bikes), manufacturing speed equipment and operating his own speed shop in his home town of Phoenix when he was still a teen.

After moving to San Diego in the 1950s, among other exploits he dropped a Hemi into a Hudson and drove it to a 157-mph speed record at Bonneville.

Inevitably, the inventive and inexhaustible Crower built up a major equipment business in superchargers, intake manifolds, clutches and, especially, camshafts. He’s also credited with first suggesting a rear wing to Don Garlits—in 1963, three years before Jim Hall’s winged Chaparral. Bruce Crower is now in Florida’s Drag Racing Hall of Fame.

Crower actually had introduced a wing two years earlier, during practice on Jim Rathmann's 1961 Indianapolis car—five years before Jim Hall’s winged Chaparral. Bruce had been crewing at the Speedway since 1954 (Jimmy Bryan, second place), and had been part of Rathmann's 1960 victory effort. He was likewise on the winning teams in 1966 (Graham Hill) and 1967 (AJ Foyt). Three decades later, in 1998, Eddie Cheever won with Crower cams.

Bruce even produced his own complete Indy engine, a flat-8 that didn’t quite make the field in 1977 and then was rendered obsolete (due to its width) by the advent of ground-effect tunnels. But the Crower 8 and its automatic clutch did win an SAE award for innovation.

Today, Crower Cams and Equipment Company employs about 160 people in five facilities, and manufactures not only cams but crankshafts and connecting rods—including titanium rods for (unnamed) Formula One customers.

Bruce Crower can’t be called retired now, but he’s happy to let the company he founded “roll along” while he “plays with cars.” That’s how he looks at the intensive R&D work he carries out in the privacy of his 13-acre horse property near the rural community of Jamul.

One of several projects is building up Honda S2000 engines for the Midget raced by his granddaughter, Ashley Swanson. (“I think she’s on par with Danica Patrick,” says the proud grampa.)

But his prime focus is proving his six-stroke engine is as revolutionary as he believes it is. “I’ve been trying to find something wrong with the whole basic idea for almost a year,” he says, “but I think we’re going to have a very marketable item.”

Then he adds philosophically, “If it turns out to be great, fine. If it doesn’t, it’s just another year out of my life that I’ve had a lot of fun doing something.”

Grail Engine

It's a very high-tech two-stroke engine that uses forced induction, direct injection and other technologies for impressive power and efficiency.

How it differs from conventional two-stroke engine ?

The engine is based on The Grail Cycle," which is a combination of one type of ignition or homogeneous charged compression ignition while simultaneously operating in the Miller Cycle.

Engine produces power every revolution per-cylinder. because of only two strokes.

The engine can operate on literally any combustible, including propane, natural gas and diesel.

 The piston and compression chamber constantly have cool air moving through the center of their masses, heat soak is reduced, which allows fuel injection to occur at any time and in turn reduces NOx emissions.

It's cheap to produce—there are very few parts involved and many can be simple castings so it is light for its power output.

The Grail Engine has the potential to be the first two stroke engine that does not exhibit cross contamination of fuel and oil. This results in lower emissions yet produces more power and torque using less fuel than larger engines.

Applications :

It could be applied to every area of life, from automobiles to aircraft, and recreational and industrial engines.

Formula One

Formula One, also known as Formula 1 or F1 and referred to officially as the FIA Formula One World Championship, is the highest class of single-seater auto racing sanctioned by the Fédération Internationale de l'Automobile (FIA). The "formula", designated in the name, refers to a set of rules with which all participants' cars must comply. The F1 season consists of a series of races, known as Grands Prix (from French, originally meaning great prizes), held throughout the world on purpose-built circuits and public roads. The results of each race are evaluated using a points system to determine two annual World Championships, one for the drivers and one for the constructors. The racing drivers, constructor teams, track officials, organisers, and circuits are required to be holders of valid Super Licences, the highest class of racing licence issued by the FIA.

Formula One cars are among the fastest circuit-racing cars in the world, owing to very high cornering speeds achieved through the generation of large amounts of aerodynamic downforce. Formula One cars race at speeds of up to 350 km/h (220 mph) with engines limited in performance to a maximum of 18,000 revolutions per minute (RPM). The cars are capable of lateral acceleration in excess of 5 g in corners. The performance of the cars is very dependent on electronics – although traction control and other driving aids have been banned since 2008 – and on aerodynamics, suspension and tyres. The formula has had much evolution and change through the history of the sport.

While Europe is the sport's traditional base, and hosts about half of each year's races, the sport's scope has expanded significantly during recent years and an increasing number of Grands Prix are held on other continents. Formula One had a total global television audience of 527 million people during the course of the 2010 FIA Formula One World Championship.

Such racing began in 1906 and, in the second half of the 20th century, became the most popular type internationally. The Formula One Group is the legal holder of the commercial rights. With annual spending totalling billions of US dollars, Formula One's economic effect and creation of jobs is significant, and its financial and political battles are widely reported. Its high profile and popularity make it a merchandising environment, which results in great investments from sponsors and budgets in the hundreds of millions for the constructors. Since 2000 the sport's spiraling expenditures have forced several teams, including manufacturers' works teams, into bankruptcy. Others have been bought out by companies wanting to establish a presence within the sport, which strictly limits the number of participant teams.

History of Cars Part D

Vintage Era (1919 - 1929)
"A vintage car is usually defined as built between the start of 1919 and through to the stock market crash at the end of 1929. There is some debate about the start date of the Vintage period-the end of World War I is a nicely defined marker there-but the end date is a matter of a little more debate.

While some American sources prefer 1925 since it is the pre-classic car period as defined by the Classic Car Club of America, the British definition is strict about 1930 being the cut-off. Others see the Classic period as overlapping the Vintage period, especially since the Vintage designation covers all vehicles produced in the period while the official Classic definition does not, only including high-end vehicles of the period. Some consider the start of World War II to be the end date of the Vintage period.

After the war, military plants were quick to retool for automobile production and the lack of government regulations for safety, the environment or employees gave it a sense of the wild Wild West. Industrial accidents were all too common and compensation was at the discretion of the employer. As such there were no vehicle requirements like windshields, doors, lights, turn signals or seat belts."

It was after the war that some famous name automobile manufactures started producing their innovative designs. Henry Ford started it with his assembly line production of the T Model Ford. As cars increased in popularity tarred roads were built by governments throughout the various countries. In Australia, however, as in many other nations, dirt roads were to persist in most places until well after the Second World War. They were gradually replaced as money allowed and even today there are many secondary roads that will not be tarred for some time. Still they are pleasant enough to drive on.

The other major factor in the success of the motor vehicle at that time was the availability of gasoline. Thousands of oil wells were springing up in USA, Europe, Asia and elsewhere. Technology was catching up as well. and during the Second World War the motor vehicle was a major defense weapon. Its speed and ability got personnel around the countryside and to their ships or planes, and so on, with little effort. The motor vehicle proved a godsend in many ways and every major nation was now heavily involved in motor vehicle production and ownership.

By that time as well as powering ground based vehicles the petrol engine was flying planes, driving boats, powering ships and allowing tanks and other such things to be manufactured. Steam was on the way out as diesel gradually replaced it.

If those early pioneers had not persisted with their dreams none of those innovations would have been possible.

History of Cars part C

Antique or Brass Era (1905 - 1914)
"The antique or brass era lasted from roughly 1905 through to the beginning of World War I in 1914. This era saw the first mass produced vehicles with gasoline engines, immortalized by Henry Ford's model T. The brass era was named for the widespread use of the fancy brass fittings and brass lanterns that adorned the new 'horseless carriage'.1905 was a signal year in the development of the automobile, marking the point when the majority of sales shifted from the hobbyist and enthusiast to the average user. Brass began to be phased out about 1914 in favor of nickel, which was eventually abandoned in favor of chrome.

Within the 15 years of this era, the various experimental designs and alternate power systems would be marginalized. Steam power proved too cumbersome and electric motors were limited by battery technology (as they still are today), but gasoline was cheap and plentiful, encouraging both two-stroke and four-stroke development."

Far from luxurious these vehicles were mainly owned by the rich. With no doors, windscreen wipers or heaters and with the inconvenience of headlights lit by a match, they must have been an encumbrance to drive around. The engine was started with a crank and in wet and windy weather it was a real horror.

My grandmother bought a car of a later type in which we motored many a happy mile. But by that time they were second hand and almost giveaways as the newer more streamlined limousines came into being. The one she purchased had doors but it started only with a crank and was very high off the ground. It had a running board on either side of the vehicle on which you first stepped to enter it. As a teenager I also had great fun as with some friends we motored around Sydney in a similar vehicle, usually laughing our head off and freezing in the drafts coming through the perspex side windows, or blinds.

They made great jalopies for the young and it is probably in that context that most people would remember them. If not physically at least through movies and television shows. The were a real thrill and it is probably why the original owners flocked to get one. As they had never seen anything better they probably did not mind the inconveniences.

"The early Model T Ford revolutionized the automotive industry with the introduction of assembly-line production, which in turn made it possible for Ford to offer their car for sale at a much more affordable price. Prior to the introduction of the Model T, automobiles were built by hand, one at a time, and usually sold for anywhere from twice the average worker's salary to several times that amount."

History of Cars Part B

Veteran Era (1888 - 1904)

"The first production of automobiles was by Karl Benz in 1888 in Germany and under license to Benz, in France by Emile Roger. By 1900 mass production of automobiles had begun in France and the United States. The first company to form exclusively to build automobiles was Panhard et Levassor in France. Formed in 1889, they were quickly followed by Peugeot two years later. In the United States, brothers Charles and Frank Duryea founded the Duryea Motor Wagon Company in 1893, becoming the first American automobile manufacturing company. However, it was Ransom E. Olds, and his Olds Motor Vehicle Company (later known as Oldsmobile) who would dominate this era of automobile production. Its large scale production line was running in 1902. Within a year, Cadillac, Winton, and Ford were producing cars in the thousands (formed from the Henry Ford Company).

"Within a few years dizzying assortments of technologies were being produced by hundreds of producers all over the western world. Steam, electricity, and gasoline-powered autos competed for decades, with gasoline internal combustion engines achieving dominance in the 1910s. Dual and even quad-engine cars were designed, and engine displacement ranged to more than a dozen liters. Many modern advances, including gas / electric hybrids, multi-valve engines, overhead camshafts, and four-wheel drive, were attempted and discarded at this time."

In 1895 a patent was granted to a USA manufacturer, Sheldon, but it may have hindered the industry in that country rather than helped it. By granting a license to successive car manufacturers afterward he collected a fee on every car produced. Well, that was probably a good business outcome for him.

There were great handicaps to motoring in those times. The roads were bad, fuel was scarce, breakdowns were frequent, and the noise of a horseless carriage frightened the hacks pulling buggies around.

Restoring one of these vehicles is fraught with difficulties. Parts are not available and usually must be hand made or located with great effort. But that has not stopped collectors from coveting them and many are restored to their former glory. At one stage there were over a thousand manufacturers in the USA alone making the task even harder.

Exhaust Theory

Jeep 2.5 liter 4-cylinder engine, chromed - close up of the exhaust manifold viewed from the bottom. This engine was developed by American Motors Corporation (AMC) and continued to be manufactured by Chrysler. All were built in Kenosha, Wisconsin. (Photo credit: Wikipedia)

Author: Myself (User:Steevven1) Originally hosted on http://www.steevven1.com/pictures.php (Photo credit: Wikipedia)

Exhaust Theory

We've seen too much misinformation regarding exhaust theory. What kind of misinformation? For starters, there are a lot of people in the "Bigger is Better" camp. We're talking about exhaust pipe diameters. Even the big magazine editors are boldly smattering statements like, "For a turbo car, you can't get an exhaust pipe that's too big." Also, terms like "back pressure" and the statement, "An engine needs back pressure to run properly!" really rub us the wrong way.

Let's start from the beginning. What is an exhaust system? Silly question? Not hardly. Exhaust systems carry out several functions. Among them are: (1) Getting hot, noxious exhaust gasses from your engine to a place away from the engine compartment; (2) Significantly attenuating noise output from the engine; and (3) In the case of modern cars, reduce exhaust emissions.

Hardware

In order to give you a really good idea of what makes up an exhaust system, let's start with what exhaust gas travels through to get out of your car, as well as some terms and definitions:

After your air/fuel mixture (or nitrous/fuel mixture) burns, you will obviously have some leftovers consisting of a few unburned hydrocarbons (fuel), carbon monoxide, carbon dioxide, nitrogen oxides, sulfur dioxide, phosphorus, and the occasional molecule of a heavy metal, such as lead or molybdenum. These are all in gaseous form, and will be under a lot of pressure as the piston rushes them out of the cylinder and into the exhaust manifold or header. They will also be hotter 'n Hades. (After all, this was the explosion of an air/fuel mixture, right?) An exhaust manifold is usually made of cast iron, and its' primary purpose is to funnel several exhaust ports into one, so you don't need four exhaust pipes sticking out the back of your Civic.

Exhaust manifolds are usually pretty restrictive to the flow of exhaust gas, and thus waste a lot of power because your pistons have to push on the exhaust gasses pretty hard to get them out. So why does virtually every new automobile sold have exhaust manifolds? Because they are cheap to produce, and easy to install. Real cheap. Real easy. Like me.

"Ok," you ask, "so now what?" Ah, good thing you asked. The performance alternative to the exhaust manifold is a header. What's the difference? Where a manifold usually has several holes converging into a common chamber to route all your gasses, a header has precisely formed tubes that curve gently to join your exhaust ports to your exhaust pipe. How does this help? First of all, as with any fluid, exhaust gasses must be treated gently for maximum horsepower production. You don't want to just slam-bang exhaust gas from your engine into the exhaust system. No way, Jo-se'! Just as the body of your '94 Eclipse is beautiful, swoopy, and aerodynamic, so must be the inside of your exhaust system.

Secondly, a header can be "tuned" to slightly alter your engines' characteristics. We'll go in-depth into header tuning a little later.

Nextly, exhaust gasses exit from your manifold or header, travel through a bit of pipe, then end up in the catalytic converter, or "cat". The cat's main job is to help clean up some of the harmful chemicals from your exhaust gas so they don't end up in your lungs. In most cars, they also do a great job of quieting things down and giving any exhaust system a deeper, mellow tone. You'll see a lot of Self-Proclaimed Master Technicians (SPMT's) telling people that removing a cat will get you tons of power. There's room for debate on this, but in our experience, removing a catalytic converter from a new car won't gain you much in the horsepower department. It can also get you a $1500 fine if the EPA finds out! If you drive an OBD-II equipped car, you'll also get that damn annoying CHECK ENGINE light burnin' up your dashboard. (And for all you racers concerned with OBD-II's fabled "limp mode", you can put your fears to rest.)

From the catalytic converter, the exhaust gasses go through a bit more pipe and then into a muffler, or system consisting of several mufflers and/or resonators.

Are you a muff?

Exhaust gases leave the engine under extremely high pressure. If we allowed exhaust gasses escape to the atmosphere directly from the exhaust port, you can well imagine how loud and cop-attracting the noise would be. For the same reason gunshots are loud, engine exhaust is loud. Sure, it might be cool to drive around on the street with that testosterone producing, chest-thumping, 150 decibel roar coming from your car… for about 5.3 seconds. (Not 5.2 or 5.4 seconds… 5.3.) Even the gentleman's gentleman has gotta use a muffler, or system of mufflers, on their exhaust.

Again, you may hear a few SPMT's tell you that "Borla mufflers make horsepower!" Or "An engine needs some backpressure to run properly!" Nonsense. A muffler can no more "make" horsepower than Wile E. Coyote can catch roadrunners. Any technician with any dyno experience will tell you that the best mufflers are no mufflers at all!

Types of Muff

Mufflers can take care of the silencing chores by three major methods: Absorption, Restriction, and Reflection. Mufflers can use one method, or all three, to attenuate sound that is not so pleasing to the ears of the Highway Patrol.

The absorption method is probably the least effective at quelling engine roar, but the benefit is that "absorbers" are also best at letting exhaust gas through. Good examples of absorbers are the mufflers found in GReddy BL-series exhausts, DynoMax UltraFlow, and the good old-fashioned Cherry Bomb glasspack.

Absorption mufflers are also the simplest. All of the above named mufflers utilize a simple construction consisting of a perforated tube that goes through a can filled with a packing material, such as fiberglass or steel wool. This is similar to simply punching holes in your exhaust pipe, then wrapping it up with insulation. Neat, huh?

Another trick absorption mufflers use to kill off noise is, well, tricky. For example, the Hooker Aero Chamber muffler is a straight-through design, with a catch. Instead of a simple, perforated tube, there is a chamber inside the muffler that is much larger than the rest of the exhaust pipe. This design abates sound more efficiently than your standard straight-through because when the exhaust gasses enter this large chamber they slow down dramatically. This gives them more time to dwell in the sound insulation, and thus absorb more noise. The large chamber gently tapers back into the smaller size of your exhaust pipe, and the exhaust gasses are sent on their merry way to the tailpipe.

Restriction

Doesn't that word just make your skin crawl? It's right up there in the same league with words like "maim" and "rape".

Obviously, a restrictive muffler doesn't require much engineering expertise, and is almost always the least expensive to manufacture. Thus, we find restrictive mufflers on almost all OEM exhaust systems. We won't waste much time on the restrictive muffler except to say that if you got 'em, you might not want to flaunt 'em.

Reflection

Probably the most sophisticated type of muffler is the reflector. They often utilize absorption principles in conjunction with reflection to make the ultimate high-performance silencer. Remember any of your junior high school math? Specifically, that like numbers cancel each other when on a criss-cross? That's the same principal used by the reflective muffler. Sound is a wave. And when two like waves collide, they will "cancel" each other and leave nothing to call a corpse but a spot of low-grade heat.

There are numerous engineering tricks used in the reflective muffler. Hedman Hedders makes a muffler that looks a lot like a glasspack. In fact, it is a glasspack with a catch. The outer casing is sized just-so, so that high-pitched engine sound (what we deem "noise") is reflected back into the core of the muffler… where those sound waves meet their maker as they slam right into a torrent of more sound waves of like wavelength coming straight from the engine. And, this muffler is packed with a lot of fiberglass to help absorb any straggling noise that might be lagging behind.

The Exhaust Pulse

To gain a more complete understanding of how mufflers and headers do their job, we must be familiar with the dynamics of the exhaust pulse itself. Exhaust gas does not come out of the engine in one continuous stream. Since exhaust valves open and close, exhaust gas will flow, then stop, and then flow again as the exhaust valve opens. The more cylinders you have, the closer together these pulses run.

Keep in mind that for a "pulse" to move, the leading edge must be of a higher pressure than the surrounding atmosphere. The "body" of a pulse is very close to ambient pressure, and the tail end of the pulse is lower than ambient. It is so low, in fact, that it is almost a complete vacuum! The pressure differential is what keeps a pulse moving. A good Mr. Wizard experiment to illustrate this is a coffee can with the metal ends cut out and replaced with the plastic lids. Cut a hole in one of the lids, point it toward a lit candle and thump on the other plastic lid. What happens? The candle flame jumps, then blows out! The "jump" is caused by the high-pressure bow of the pulse we just created, and the candle goes out because the trailing portion of the pulse doesn't have enough oxygen-containing air to support combustion. Neat, huh?

Ok, now that we know that exhaust gas is actually a series of pulses, we can use this knowledge to propagate the forward-motion to the tailpipe. How? Ah, more of the engineering tricks we are so fond of come in to play here.

Just as Paula Abdul will tell you that opposites attract, the low pressure tail end of an exhaust pulse will most definitely attract the high-pressure bow of the following pulse, effectively "sucking" it along. This is what's so cool about a header. The runners on a header are specifically tuned to allow our exhaust pulses to "line up" and "suck" each other along! Whoa, bet you didn't know that! This brings up a few more issues, since engines rev at various speeds, the exhaust pulses don't always exactly line up. Thus, the reason for the Try-Y header, a 4-into-1 header, etc. Most Honda headers are tuned to make the most horsepower in high RPM ranges; usually 4,500 to 6,500 RPM. A good 4-into-1 header, such as the ones sold by Gude, are optimal for that high winding horsepower you've always dreamed of. What are exhaust manifolds and stock exhaust systems good for? Besides a really cheap boat anchor? If you think about it, you'll realize that since stock exhausts are so good at restricting that they'll actually ram the exhaust pulses together and actually make pretty darn good low-end torque! Something to keep in mind, though, is that even though an OEM exhaust may make gobs of low-end torque, they are not the most efficient setup overall, since your engine has to work so hard to expel those exhaust gasses. Also, a header does a pretty good job of additionally "sucking" more exhaust from your combustion chamber, so on the next intake stroke there's lots more fresh air to burn. Think of it this way: At 8,000 RPM, your Integra GS-R is making 280 pulses per second. There's a lot more to be gained by minimizing pumping losses as this busy time than optimizing torque production during the slow season.

General Rules of Thumb with Headers

You will undoubtedly see a variety of headers at your local speed shop. While you won't be able to determine the optimal power range of the headers by eyeballing them, you'll find that in general, the best high-revving horsepower can be had with headers utilizing larger diameter, shorter primary tubes. Headers with smaller, longer primaries will get you
slightly better fuel economy and better street driveability. With four cylinder engines, these are also usually of the Tri-Y design, such as the DC Sports and Lightspeed headers.

Do Mufflers "Make" Horsepower?

The answer, simply, is no. The most efficient mufflers can only employ the same scavenging effect as a header, to help slightly overcome the loss of efficiency introduced into the system as back pressure. But I have yet to see an engine that made more power with a muffler than an open header exhaust. "So," you ask, "what the hell is the best flowing muffler I can buy?"

According to the flowbench, two of the best flowing units you can buy are the Walker Dyno Max and the Cyclone Sonic. They even slightly out flow the straight through designs from HKS and GReddy BL series. Amongst the worst, are the Thrush Turbo and Flow Master mufflers. We'll flow some of the newer mufflers as they become available at our local Chief auto.

Resonators

On your typical cat-back exhaust system, you'll see a couple of bulges in the piping that are apparently mini-mufflers out to help the big muffler that hangs out back. These are called Helmholtz Resonators and are very similar to glasspacks. The main difference is that firstly, there is no sound-absorbing fiberglass or steel wool in a Resonator. And secondly, their main method of silencing is the reflective principle, not absorption. An easy way to tell the difference between a glasspack and a true Helmholtz Resonator is to "ping" one with your finger. A glasspack will make a dull thud, and a true Resonator will make a clear "ping!" sound.

Turbos

Another object that might be sitting in your exhaust flow is a turbine from a turbocharger. If that is the case, we envy you.

Not only that, but turbos introduce a bit of backpressure to your exhaust system, thus making it a bit quieter. All of the typical scavenging rules still apply, but with a twist. Mufflers work really well now! Remember, one of the silencing methods is restriction, and a turbine is just that, a restriction.

This is actually where the term "turbo muffler" is coined. Since a turbine does a pretty good job of silencing, OEM turbo mufflers can do a lot less restricting to quiet things down. Of course, aftermarket manufacturers took advantage of this performance image and branded a lot of their products with the "turbo" name in order to drum up more business from the high performance crowd. We're sad to say that the term "turbo" has been bastardized in this respect, and would like that to serve as a warning. A "turbo" muffler is not necessarily a high-performance muffler.

Pipe Sizing

We've seen quiet a few "experienced" racers tell people that a bigger exhaust is a better exhaust. Hahaha… NOT.

As discussed earlier, exhaust gas is hot. And we'd like to keep it hot throughout the exhaust system. Why? The answer is simple. Cold air is dense air, and dense air is heavy air. We don't want our engine to be pushing a heavy mass of exhaust gas out of the tailpipe. An extremely large exhaust pipe will cause a slow exhaust flow, which will in turn give the gas plenty of time to cool off en route. Overlarge piping will also allow our exhaust pulses to achieve a higher level of entropy, which will take all of our header tuning and throw it out the window, as pulses will not have the same tendency to line up as they would in a smaller pipe. Coating the entire exhaust system with an insulative material, such as header wrap or a ceramic thermal barrier coating reduces this effect somewhat, but unless you have lots of cash burning a hole in your pocket, is probably not worth the expense on a street driven car.

Unfortunately, we know of no accurate way to calculate optimal exhaust pipe diameter. This is mainly due to the random nature of an exhaust system -- things like bends or kinks in the piping, temperature fluctuations, differences in muffler design, and the lot, make selecting a pipe diameter little more than a guessing game. For engines making 250 to 350 horsepower, the generally accepted pipe diameter is 3 to 3 � inches. Over that amount, you'd be best off going to 4 inches. If you have an engine making over 400 to 500 horsepower, you'd better be happy capping off the fun with a 4 inch exhaust. Ah, the drawbacks of horsepower. The best alternative here would probably be to just run open
exhaust! 

Other Rules

A lot of the time, you'll hear someone talking about how much hotter the exhaust system on a turbo car gets than a naturally aspirated car. Well, if you are catching my drift so far, you'll know that this is a bunch of BS. The temperature of exhaust gas is controlled by air/fuel mixture, spark, and cam timing. Not the turbo hanging off the exhaust manifold.

When designing an exhaust system, turbocharged engines follow the same rules as naturally aspirated engines. About the only difference is that the turbo engine will require quite a bit less silencing.

Another thing to keep in mind is that, even though it would be really super cool to get a 4 inch, mandrel bent exhaust system installed under your car, keep in mind that all of that beautiful art work won't do you a bit of good if the piping is so big that it gets punctured as you drag it over a speed bump! A good example of this is the 3 inch, cat back system sold by Thermal Research and Development for the Talon/Laser/Eclipse cars. The piping is too big to follow the stock routing exactly, and instead of going up over the rear suspension control arms, it hangs down below the mechanicals, right there in reach of large rocks! So when designing your Ultimate Exhaust System, do be careful!

Related articles

• Scientists create inexpensive new thermoelectric material

How Mufflers Work

Mufflers cancel out most of an engine's noise.

If you've ever heard a car engine running without a muffler, you know what a huge difference a muffler can make to the noise level. Inside a muffler, you'll find a deceptively simple set of tubes with some holes in them. These tubes and chambers are actually as finely tuned as a musical instrument. They are designed to reflect the sound waves produced by the engine in such a way that they partially cancel themselves out.

Mufflers use some pretty neat technology to cancel out the noise. In this article, we'll take a look inside a real car muffler and learn about the principles that make it work.

But first, we need to know a little about sound. 

Where Does the Sound Come From?

Sound is a pressure wave formed from pulses of alternating high and low air pressure. These pulses makes their way through the air at -- you guessed it -- the speed of sound.

In an engine, pulses are created when an exhaust valve opens and a burst of high-pressure gas suddenly enters the exhaust system. The molecules in this gas collide with the lower-pressure molecules in the pipe, causing them to stack up on each other. They in turn stack up on the molecules a little further down the pipe, leaving an area of low pressure behind. In this way, the sound wave makes its way down the pipe much faster than the actual gases do.

When these pressure pulses reach your ear, the eardrum vibrates back and forth. Your brain interprets this motion as sound. Two main characteristics of the wave determine how we perceive the sound:

• Sound wave frequency - A higher wave frequency simply means that the air pressure fluctuates faster. The faster an engine runs, the higher the pitch we hear. Slower fluctuations sound like a lower pitch.
• Air pressure level - The wave's amplitude determines how loud the sound is. Sound waves with greater amplitudes move our eardrums more, and we register this sensation as a higher volume.

It turns out that it is possible to add two or more sound waves together and get less sound. Let's see how.

How Can You Cancel Out Sound?

The key thing about sound waves is that the result at your ear is the sum of all the sound waves hitting your ear at that time. If you are listening to a band, even though you may hear several distinct sources of sound, the pressure waves hitting your ear drum all add together, so your ear drum only feels one pressure at any given moment.

Now comes the cool part: It is possible to produce a sound wave that is exactly the opposite of another wave. This is the basis for those noise-canceling headphones you may have seen. Take a look at the figure below. The wave on top and the second wave are both pure tones. If the two waves are in phase, they add up to a wave with the same frequency but twice the amplitude. This is called constructive interference. But, if they are exactly out of phase, they add up to zero. This is called destructive interference. At the time when the first wave is at its maximum pressure, the second wave is at its minimum. If both of these waves hit your ear drum at the same time, you would not hear anything because the two waves always add up to zero.

How sound waves add and subtract

In the next section, we'll see how the muffler is designed to create waves that cause as much destructive interference as possible.

Inside a Muffler

Located inside the muffler is a set of tubes. These tubes are designed to create reflected waves that interfere with each other or cancel each other out. Take a look at the inside of this muffler:

The exhaust gases and the sound waves enter through the center tube. They bounce off the back wall of the muffler and are reflected through a hole into the main body of the muffler. They pass through a set of holes into another chamber, where they turn and go out the last pipe and leave the muffler.

A chamber called a resonator is connected to the first chamber by a hole. The resonator contains a specific volume of air and has a specific length that is calculated to produce a wave that cancels out a certain frequency of sound. How does this happen? Let's take a closer look ...

The Resonator

When a wave hits the hole, part of it continues into the chamber and part of it is reflected. The wave travels through the chamber, hits the back wall of the muffler and bounces back out of the hole. The length of this chamber is calculated so that this wave leaves the resonator chamber just after the next wave reflects off the outside of the chamber. Ideally, the high-pressure part of the wave that came from the chamber will line up with the low-pressure part of the wave that was reflected off the outside of the chamber wall, and the two waves will cancel each other out.

The animation below shows how the resonator works in a simplified muffler.

Waves canceling inside a simplified muffler

In reality, the sound coming from the engine is a mixture of many different frequencies of sound, and since many of those frequencies depend on the engine speed, the sound is almost never at exactly the right frequency for this to happen. The resonator is designed to work best in the frequency range where the engine makes the most noise; but even if the frequency is not exactly what the resonator was tuned for, it will still produce some destructive interference.

Some cars, especially luxury cars where quiet operation is a key feature, have another component in the exhaust that looks like a muffler, but is called a resonator. This device works just like the resonator chamber in the muffler -- the dimensions are calculated so that the waves reflected by the resonator help cancel out certain frequencies of sound in the exhaust.

There are other features inside this muffler that help it reduce the sound level in different ways. The body of the muffler is constructed in three layers: Two thin layers of metal with a thicker, slightly insulated layer between them. This allows the body of the muffler to absorb some of the pressure pulses. Also, the inlet and outlet pipes going into the main chamber are perforated with holes. This allows thousands of tiny pressure pulses to bounce around in the main chamber, canceling each other out to some extent in addition to being absorbed by the muffler's housing.

The exhaust from a NASCAR race car: There are no mufflers here, because reducing backpressure is the name of the game.

Backpressure and Other Types of Mufflers

One important characteristic of mufflers is how much backpressure they produce. Because of all of the turns and holes the exhaust has to go through, mufflers like those in the previous section produce a fairly high backpressure. This subtracts a little from the power of the engine.

There are other types of mufflers that can reduce backpressure.

One type, sometimes called a
 glass pack or a cherry bomb, uses only absorption to reduce the sound. On a muffler like this, the exhaust goes straight through a pipe that is perforated with holes. Surrounding this pipe is a layer of glass insulation that absorbs some of the pressure pulses. A steel housing surrounds the insulation.

                                                                                     

Active Noise-Canceling Mufflers

There have been a few experiments with active noise-canceling mufflers, especially on industrial generators. These systems incorporate a set of microphones and a speaker.

The speaker is positioned in a pipe, which wraps around the exhaust pipe so that the sound from the exhaust comes out in the same direction as the sound from the speaker. A computer monitors a microphone positioned before the speaker and one positioned after the speaker. By knowing some things about the length and shape of the pipes, the computer can generate a signal to drive the speaker. This can cancel out much of the sound coming from the generator. The downstream microphone lets the computer know how well it is doing so it can make adjustments if needed.

For further readings kindly have a look at these links :

http://www.auto.mechies.in/2013/01/exhaust-theory.html

http://en.wikipedia.org/wiki/Muffler

AWD and 4WD : Whats the Difference ??

                                                             

All-Wheel Drive (AWD)

All-wheel drive transmits power to all four wheels all the time. Combined with modern traction control technology, an AWD vehicle will transfer power to the wheels with the most grip in slippery conditions. The primary disadvantage to AWD vehicles is fuel economy, as there is added weight in an AWD arrangement.
AWD is ideal for daily commuters who live in climates with a lot of snow and rain and who may occasionally drive on dirt or gravel.


Four-Wheel Drive (4WD)

Four-wheel drive functions the same as an AWD system, but a four-wheel drive vehicle will be equipped with one of two options: part-time 4WD or full-time 4WD. Part-time 4WD is designed so the driver can designate when to use 4WD and when to use two-wheel drive.

For example, while off-roading or driving off pavement, 4WD is typically a better option for control, whereas, 4WD isn’t as efficient and can actually be harder on the vehicle when used on pavement.

A full-time 4WD system is designed to power all four wheels on any terrain and is intended for trucks that will be used in heavy snow or be primarily driven off-road. While 4WD is similar to AWD, full-time 4WD systems often give drivers the option to use “high” for higher speeds and “low” when creeping through a puddle of mud or driving over big rocks. AWD is less proficient than 4WD when off-roading.

4WD is ideal for OKC Truck and Car drivers who need a tough and rugged vehicle to be driven off road or in harsh weather conditions.

Dual Overhead Camshafts (DOHC)
    A DOHC engine has two camshafts in each cylinder head; one camshaft actuates intake valves and the other actuates exhaust valves. The camshafts act directly on the valves, eliminating pushrods and rocker arms. This reduced reciprocating mass of the valve train enables the engine to build RPM more quickly. DOHC designs are typically high-performance, four valve per cylinder engines. (A four valve per cylinder two intake and two exhaust design helps the engine "breathe" more freely for increased performance.)

Caster , Camber , Toe in & out

THE EFFECTS OF CASTER

Caster is the angle to which the steering pivot axis is tilted forward or rearward from vertical, as viewed from the side. If the pivot axis is tilted backward (that is, the top pivot is positioned farther rearward than the bottom pivot), then the caster is positive; if it's tilted forward, then the caster is negative.

Positive caster tends to straighten the wheel when the vehicle is traveling forward, and thus is used to enhance straight-line stability. The mechanism that causes this tendency is clearly illustrated by the castering front wheels of a shopping cart (above). The steering axis of a shopping cart wheel is set forward of where the wheel contacts the ground. As the cart is pushed forward, the steering axis pulls the wheel along, and since the wheel drags along the ground, it falls directly in line behind the steering axis. The force that causes the wheel to follow the steering axis is proportional to the distance between the steering axis and the wheel-to-ground contact patch-the greater the distance, the greater the force. This distance is referred to as "trail."

Due to many design considerations, it is desirable to have the steering axis of a car's wheel right at the wheel hub. If the steering axis were to be set vertical with this layout, the axis would be coincident with the tire contact patch. The trail would be zero, and no castering would be generated. The wheel would be essentially free to spin about the patch (actually, the tire itself generates a bit of a castering effect due to a phenomenon known as "pneumatic trail," but this effect is much smaller than that created by mechanical castering, so we'll ignore it here). Fortunately, it is possible to create castering by tilting the steering axis in the positive direction. With such an arrangement, the steering axis intersects the ground at a point in front of the tire contact patch, and thus the same effect as seen in the shopping cart casters is achieved.

The tilted steering axis has another important effect on suspension geometry. Since the wheel rotates about a tilted axis, the wheel gains camber as it is turned. This effect is best visualized by imagining the unrealistically extreme case where the steering axis would be horizontal-as the steering wheel is turned, the road wheel would simply change camber rather than direction. This effect causes the outside wheel in a turn to gain negative camber, while the inside wheel gains positive camber. These camber changes are generally favorable for cornering, although it is possible to overdo it.

Most cars are not particularly sensitive to caster settings. Nevertheless, it is important to ensure that the caster is the same on both sides of the car to avoid the tendency to pull to one side. While greater caster angles serve to improve straight-line stability, they also cause an increase in steering effort. Three to five degrees of positive caster is the typical range of settings, with lower angles being used on heavier vehicles to keep the steering effort reasonable.

Like a shopping cart wheel (left) the trail created by the castering of the steering axis pulls the wheels in line.

WHAT IS CAMBER?

Camber is the angle of the wheel relative to vertical, as viewed from the front or the rear of the car. If the wheel leans in towards the chassis, it has negative camber; if it leans away from the car, it has positive camber (see next page). The cornering force that a tire can develop is highly dependent on its angle relative to the road surface, and so wheel camber has a major effect on the road holding of a car. It's interesting to note that a tire develops its maximum cornering force at a small negative camber angle, typically around neg. 1/2 degree. This fact is due to the contribution of camber thrust, which is an additional lateral force generated by elastic deformation as the tread rubber pulls through the tire/road interface (the contact patch).

To optimize a tire's performance in a corner, it's the job of the suspension designer to assume that the tire is always operating at a slightly negative camber angle. This can be a very difficult task, since, as the chassis rolls in a corner, the suspension must deflect vertically some distance. Since the wheel is connected to the chassis by several links which must rotate to allow for the wheel deflection, the wheel can be subject to large camber changes as the suspension moves up and down. For this reason, the more the wheel must deflect from its static position, the more difficult it is to maintain an ideal camber angle. Thus, the relatively large wheel travel and soft roll stiffness needed to provide a smooth ride in passenger cars presents a difficult design challenge, while the small wheel travel and high roll stiffness inherent in racing cars reduces the engineer's headaches.

It's important to draw the distinction between camber relative to the road, and camber relative to the chassis. To maintain the ideal camber relative to the road, the suspension must be designed so that wheel camber relative to the chassis becomes increasingly negative as the suspension deflects upward. The illustration on the bottom of page 46 shows why this is so. If the suspension were designed so as to maintain no camber change relative to the chassis, then body roll would induce positive camber of the wheel relative to the road. Thus, to negate the effect of body roll, the suspension must be designed so that it pulls in the top of the wheel (i.e., gains negative camber) as it is deflected upwards.

While maintaining the ideal camber angle throughout the suspension travel assures that the tire is operating at peak efficiency, designers often configure the front suspensions of passenger cars so that the wheels gain positive camber as they are deflected upward. The purpose of such a design is to reduce the cornering power of the front end relative to the rear end, so that the car will understeer in steadily greater amounts up to the limit of adhesion. Understeer is inherently a much safer and more stable condition than oversteer, and thus is preferable for cars intended for the public.

Since most independent suspensions are designed so that the camber varies as the wheel moves up and down relative to the chassis, the camber angle that we set when we align the car is not typically what is seen when the car is in a corner. Nevertheless, it's really the only reference we have to make camber adjustments. For competition, it's necessary to set the camber under the static condition, test the car, then alter the static setting in the direction that is indicated by the test results.

The best way to determine the proper camber for competition is to measure the temperature profile across the tire tread immediately after completing some hot laps. In general, it's desirable to have the inboard edge of the tire slightly hotter than the outboard edge. However, it's far more important to ensure that the tire is up to its proper operating temperature than it is to have an "ideal" temperature profile. Thus, it may be advantageous to run extra negative camber to work the tires up to temperature.

(TOP RIGHT) Positive camber: The bottoms of the wheels are closer together than the tops. (TOP LEFT) Negative camber: The tops of the wheels are closer together than the bottoms. (CENTER) When a suspension does not gain camber during deflection, this causes a severe positive camber condition when the car leans during cornering. This can cause funky handling. (BOTTOM) Fight the funk: A suspension that gains camber during deflection will compensate for body roll. Tuning dynamic camber angles is one of the black arts of suspension tuning.

UNDERSTANDING TOE

When a pair of wheels is set so that their leading edges are pointed slightly towards each other, the wheel pair is said to have toe-in. If the leading edges point away from each other, the pair is said to have toe-out. The amount of toe can be expressed in degrees as the angle to which the wheels are out of parallel, or more commonly, as the difference between the track widths as measured at the leading and trailing edges of the tires or wheels. Toe settings affect three major areas of performance: tire wear, straight-line stability and corner entry handling characteristics.

For minimum tire wear and power loss, the wheels on a given axle of a car should point directly ahead when the car is running in a straight line. Excessive toe-in or toe-out causes the tires to scrub, since they are always turned relative to the direction of travel. Too much toe-in causes accelerated wear at the outboard edges of the tires, while too much toe-out causes wear at the inboard edges.

So if minimum tire wear and power loss are achieved with zero toe, why have any toe angles at all? The answer is that toe settings have a major impact on directional stability. The illustrations at right show the mechanisms involved. With the steering wheel centered, toe-in causes the wheels to tend to roll along paths that intersect each other. Under this condition, the wheels are at odds with each other, and no turn results.

When the wheel on one side of the car encounters a disturbance, that wheel is pulled rearward about its steering axis. This action also pulls the other wheel in the same steering direction. If it's a minor disturbance, the disturbed wheel will steer only a small amount, perhaps so that it's rolling straight ahead instead of toed-in slightly. But note that with this slight steering input, the rolling paths of the wheels still don't describe a turn. The wheels have absorbed the irregularity without significantly changing the direction of the vehicle. In this way, toe-in enhances straight-line stability.

If the car is set up with toe-out, however, the front wheels are aligned so that slight disturbances cause the wheel pair to assume rolling directions that do describe a turn. Any minute steering angle beyond the perfectly centered position will cause the inner wheel to steer in a tighter turn radius than the outer wheel. Thus, the car will always be trying to enter a turn, rather than maintaining a straight line of travel. So it's clear that toe-out encourages the initiation of a turn, while toe-in discourages it.

With toe-in (left) a deflection of the suspension does not cause the wheels to initiate a turn as with toe-out (right).

The toe setting on a particular car becomes a tradeoff between the straight-line stability afforded by toe-in and the quick steering response promoted by toe-out. Nobody wants their street car to constantly wander over tar strips-the never-ending steering corrections required would drive anyone batty. But racers are willing to sacrifice a bit of stability on the straightaway for a sharper turn-in to the corners. So street cars are generally set up with toe-in, while race cars are often set up with toe-out.

With four-wheel independent suspension, the toe must also be set at the rear of the car. Toe settings at the rear have essentially the same effect on wear, directional stability and turn-in as they do on the front. However, it is rare to set up a rear-drive race car toed out in the rear, since doing so causes excessive oversteer, particularly when power is applied. Front-wheel-drive race cars, on the other hand, are often set up with a bit of toe-out, as this induces a bit of oversteer to counteract the greater tendency of front-wheel-drive cars to understeer.

Remember also that toe will change slightly from a static situation to a dynamic one. This is is most noticeable on a front-wheel-drive car or independently-suspended rear-drive car. When driving torque is applied to the wheels, they pull themselves forward and try to create toe-in. This is another reason why many front-drivers are set up with toe-out in the front. Likewise, when pushed down the road, a non-driven wheel will tend to toe itself out. This is most noticeable in rear-drive cars.

The amount of toe-in or toe-out dialed into a given car is dependent on the compliance of the suspension and the desired handling characteristics. To improve ride quality, street cars are equipped with relatively soft rubber bushings at their suspension links, and thus the links move a fair amount when they are loaded. Race cars, in contrast, are fitted with steel spherical bearings or very hard urethane, metal or plastic bushings to provide optimum rigidity and control of suspension links. Thus, a street car requires a greater static toe-in than does a race car, so as to avoid the condition wherein bushing compliance allows the wheels to assume a toe-out condition.

It should be noted that in recent years, designers have been using bushing compliance in street cars to their advantage. To maximize transient response, it is desirable to use a little toe-in at the rear to hasten the generation of slip angles and thus cornering forces in the rear tires. By allowing a bit of compliance in the front lateral links of an A-arm type suspension, the rear axle will toe-in when the car enters a hard corner; on a straightaway where no cornering loads are present, the bushings remain undistorted and allow the toe to be set to an angle that enhances tire wear and stability characteristics. Such a design is a type of passive four-wheel steering system.