Here is a good article that I found on another site while playing around on the web. It is a really good read and can help you decide what you want to do when the time to choose a new clutch rolls around…
I have added a flash program to the bottom of this that shows how a clutch works IN DETAIL. It is a pretty cool little program.
CLUTCH BASICS
So you’re looking for a clutch, and you decide to call your local speed performance shop to discuss you’re options. The first questions you need to ask yourself are, “How much power am I making and how streetable do I want my car to be?”. There are several options ranging from clutch kits that utilize pressure plates to increase torque handling capacity, clutch kits that utilize clutch discs to increase torque handling capacity, and clutch kits that utilize both the pressure plate and the clutch disc. You also have to decide whether you want the center section on the clutch disc to be sprung or un sprung. Choosing the right combination will yield impeccable results that will show in your 60 foot times and when driving around town. Choosing the wrong combination will result in a car that is barely driveable on the street.
Rule # 1. Don’t go overboard when selecting a clutch. Often times people choose the meanest, heavy duty, gripping clutch combination out there. After their " top gun" clutch is installed, they find that they have far too much clutch. They’ll experience difficulty launching in 1st gear because the clutch wants to “grab”, and smooth engagement becomes a thing of the past. Trying to ease off the clutch results in either a terrible bog with your dashboard shaking from chatter, or your tires chirping from clutch engagement happening too harshly.
Rule # 2. Don’t go to radical on the clutch disc for a street driven application. On a disc, the higher the friction rate, the higher chance it will chatter. “Pucks”, “pads”, or “buttons”, will always have a higher friction rate than a full face disc. It’s always better to go with an organic full face disc coupled with a pressure plate that will increase torque handling capacity on a street driven application.
Some people think that the more pucks you have, the better bite you’ll get, when in fact, it is the other way around. The less pucks you have on a disc, the greater the bite. Just think of it in terms of PSI. If you have 6 pucks on a disc, then you have X amount of PSI (delivered by the pressure plate) to be distributed among those 6 pucks to the flywheel. If you have 4 pucks, then the pressure plate will have to distribute that same amount of PSI onto four pucks, so the grip rate multiplies per puck. This also creates more heat per puck thus increasing the friction rate.
Three and four puck discs are designated for drag only vehicles that spend most of their time on a trailer. These vehicles produce so much torque that it’s their only choice. I’m not saying that a street driven vehicle can’t run a four puck because there are several people that run them and drive their cars on a daily basis. It just makes life harder when in sitting in traffic due to the hard engagement and anxiousness to bite. These discs are available for when the upgraded pressure plate alone can not hold the increased torque output of a full race motor. Running a three or four puck disc will also increase the shock that the driveline sees which results in; premature wear of the axles, constant velocity joints, transmission, and motor mounts.
Six puck discs are available to those who want a disc that will hold a great deal of torque such as in high output turbocharged vehicles that see the track on a regular basis. These are somewhat tolerable on the street but still exhibit the traits of three and four puck discs. Engagement is a little smoother than a four puck, but still harsh enough to be considered a race only clutch.
A full face disc is the choice for those seeking the smoothest engagement possible. This does not mean that you can not go fast with a full face disc. For example, Tim Swytzer has used a full face disc coupled with an ACT pressure plate to gain 10 second status in his full street trim Talon. A full face disc, when coupled with a heavy duty pressure plate, allows for a killer street and strip combination. For all wheel drive vehicles, this is an excellent combination allowing dramatic 60 foots while still providing enough of a “fuse” to keep the drive train intact. It is also a good combination for those seeking a good street clutch that will provide enough slip to keep the tires hooked up.
Slipping is good to a certain extent. Front wheel drag racers that compete on street tires know that keeping the tires hooked up is important, so a clutch that provides enough slip and enough grip is crucial. A clutch combination that would engage to harsh would result in wheel spin, no matter how hard the owner tries to slip it.
SPRUNG OR UNSPRUNG?
According to a handbook printed by the Society of Automotive Engineers (SAE), sprung center section discs have evolved as a result to combat crankshaft torsional vibrations. There is this common misconception that the springs are there to reduce “chatter”, a word the clutch industry has developed which describes the quick jerking action of the motor when the clutch wants to grab the flywheel. They don’t reduce chatter but they actually increase it in most applications!. When an internal combustion motor spins, it’s crankshaft produces a lot of oscillation. This oscillation is then transferred to the transmission which results in gear noise. The damper springs were added on the clutch disc to reduce the vibrations that were transmitted from the crank to the gears, in order to reduce gear noise. These damper springs work great with a stock disc and a stock pressure plate combination because they are designed to absorb vibration at a stock friction rate. When the friction rate is increased, as in a performance clutch, chatter occurs. The engineers who designed your stock clutch and stock pressure plate combination spent countless hours finding the right spring rate which allows torsional vibration absorption and chatter free operation. Therefore, when you upgrade to a performance clutch, the spring rates are unchanged on most performance discs, but the friction rate is increased through the use of pucks and/or metallic facings, so the end result is a clutch that will chatter.
“Wait!, I have a solid hub disc and I still experience chatter!!” you might be saying. There are two reasons this will happen. One, during installation of the new solid hub clutch disc, some less experienced do it yourselfers will tend to leave the transmission hanging on the input shaft alone! Don’t do this with a solid hub disc (or any disc for that matter) because it doesn’t allow for any slack. When the tranny is left hanging for undetermined amounts of time before it gets bolted up safely, the weight of the tranny being supported by the input shaft will bend the center of solid hub discs, resulting in a disc that will chatter. Sprung hubs don’t experience this dilemma because the springs allow for some sort of “give.” Regardless of which hub you choose, you should have a professional shop do the install and insure a tranny jack is used. The second reason you will experience chatter with a solid hub disc is your motor mounts have failed or are not strong enough to keep the engine in place. Flexible engine mounts were used in vehicles to prevent high speed vibrations from the engine to the frame and body of the vehicle. When the clutch is engaged, the engine will rock back and forth on these flexible engine mounts very quickly giving you chatter. Stiffer aftermarket engine mounts are available to reduce chatter for most vehicles.
I went through AEM, ACT, Centerforce, and Clutchmasters in a quest to find the ultimate clutch combination out there that combines smooth engagement and high torque capability. The truth is there is no one particular superman clutch that can do it all for every vehicle. In fact one manufacturer went on to admit that “I believe that there are clutch kits available from different manufacturers that perform better than ours in certain applications, but at the same time, we have clutch kits that perform better than theirs”. All manufacturers have different stages for different levels of performance.
AEM
AEM, distributer of Exedy clutches, provides two different stages for the performance enthusiast. Steve Trinkaus of AEM recommends the Exedy organic clutch kit for road racers and those producing up to 100 HP over stock. The Exedy cera-metallic clutch kit is recommend for applications where high amounts of Nitrous Oxide and/or high horsepower turbo applications are being used. The Exedy clutch kits come with a 1 year /12,000 mile limited warranty against manufacturers defects. Exedy is the performance branch of Daiken, which is the OEM manufacturer of clutch kits for most japanese auto manufacturers. These clutches are pending SFI approval.
ACT
ACT offers several different options of clutches for mildly modded to high output full race vehicles. For a turbocharged Honda Civic, slap in the ACT HD pressure plate with their Xtreme solid hub four puck disc for quick shifts at high rpms and rest assure knowing that it will hold up to 300 ft lbs of torque. For those looking for something a little less extreme, you can run the six puck or a full face disc and enjoy smoother enagagement. ACT has been working closely with DSM tuner Dave Buscher in order to provide what the DSM group feels to be is the “Ultimate Street and Strip clutch”. Dave Buscher goes on to say, “I have three DSMs running in the 10 sec realm with ACT clutch kits.” ACT warrants their clutch kits against mechanical defects for up to 90 days. The solid hub lightweight aluminum design,of their Xtreme discs allow for some of the quickest high RPM shifting you will experience in a manual transmission.
CENTERFORCE
Gene Humrick of Centerforce states they have three different options for racer. The Centerforce Gold which will provide up to a 30 percent increase in holding capacity is a good replacement for those looking for an OEM replacement. The Centerforce II provides a 60 percent increase in holding capacity which is good for those running minor upgrades such as bolt ons and a light shot of nitrous. The Centerforce Dual Friction provides up to a 90 percent increase in holding capacity which is good for mildly turbocharged vehicles or those running moderate shots of Nitrous. Centerforce uses weights on their pressure plates that increase torque holding capacity as the RPMs go up, allowing a light pedal feel. You really don’t know it’s a performance clutch until you realize that you’re boosting 18 PSI and the clutch hasn’t slipped yet. They also provide a 90 day warranty against defects and material workmanship.
CLUTCHMASTERS
Clutchmasters has five stages of clutch selection. Stage 1 combines their Heavy Duty Pressure Plate with a stock disc and allows enough holding capacity for minor bolt ons and a 50 shot of Nitrous. Stage 2 adds Kevlar to the disc which allows for a longer life expectancy, but requires a critical break in procedure. It was designed to be used with mildly turbocharged vehicles or those running light shots of NOS (50 shot). Stage 3 was designed for vehicles running high output turbochargers, or high doses of NOS ( up to 100 shot). It utilizes a segmented Kevlar disc (same friction composition as stage 2 through a reduction of face material up to 40% on the disc) that is slightly more aggressive than the stage 2 but retains the life expectancy. Stage 4 is reserved for those packing extremely high output turbo systems, and/or extremely high amounts of nitrous (above 100 shot). Their stage 5 is there for those who want the clutch that will “hold it all”, as stated by Chris Jewel, owner of Clutchmasters. Don’t expect to be happy with this one on the street because it is a race clutch meant to hold all the power you can make. Chris Jewel went on to state that his clutches can be found on 7 of the top 12 quickest Hondas. There is a 45 day warranty against manufacturers defect on all his products, but he insists on 100% customer satisfaction.
So there you have it. There is a lot more to choosing a clutch then just picking up the phone and saying , “Give me the baddest one you got!.” You have to properly analyze your goals with your vehicle. Whether it be drag racing, road racing, or just plain old spirited driving around town, you need to make sure that your salesperson is clear on what you’re needs are. Most importantly, you need to be sure that you are clear on what your needs are.
I hope you guys like what you read. There is a lot of good information in there so if you skipped over any of it you should go back and read it.
I found the original article at this link if anyone really cares.
Here is that flash program of how the clutch works. Pretty neat, just click here to see it. Much thanks to Exedy for creating this flash.
ARCHIVETHIS
Later,
BR