Join Date: Jul 2004 Location: Las Vegas, NV
Posts: 3,067
| FYI: What Should I Get? (Clutches & Flywheels Explained)
What is some good background clutch information?
The first impulse when clutch shopping is to get "too much" clutch. This is often a very big mistake, as there will be compromises in the different types and compositions of clutches.
Clutches hold Torque, not horsepower
Most performance enthusiasts relate more to horsepower numbers rather than torque, but clutch capacity is measured in terms of torque. Think in terms of a high rpm 250 HP Honda civic versus a 250 HP Ford Powerstroke turbo diesel. The truck will need about three times the clutch capacity because the engine produces about three times the torque.
Choosing what’s best for you:
It may be difficult to know what clutch is right for a particular application since there are so many different levels of personal tolerance and many variations in design. Some people can tolerate clutch chatter, or noise, or heavy pedal effort, or shorter clutch life, higher cost, or other trade-offs. But why tolerate unnecessary issues if you don’t have to? Get the clutch that suits your needs.
What are the various clutch materials? Other than unique or specialized compositions, clutches are generally comprised of:
1. Organic
2. Kevlar
3. Ceramic
4. Feramic
5. Carbon (initially invented in 1998 by Alcon Components for the Subaru World Rally team )
6. Sintered Iron
Depending on manufacturer specifications, this list also shows the general order of the amount of force the clutch materials can hold.
Organic: Metal-fiber woven into "organic" (actually CF aramid with other materials), original-equipment style. Known for smooth engagement, long life, broad operating temperature, minimal-to-no break in period. Will take hard use, somewhat intolerant of repeated abuse (will overheat). Will return to almost full operational condition if overheated. Material is dark brown or black with visible metal fibers.
Kevlar: High-durability material more resistant to hard use. Engagement is similar to organic, but may glaze slightly in stop and go traffic, resulting in slippage until worn clean when used hard again. Higher temp range in general, but can be ruined from overheating; will not return to original characteristics if "cooked". Material is uniform yellow/green and may look slightly fuzzy when new.
Ceramic: Very high temperature material. Engagement is more abrupt. Will wear flywheel surface faster, especially in traffic situations. Due to it’s intrinsic properties, ceramic has a very high temperature range. Material is any of several light hues - gray, pink, brown.
Feramic: This unique clutch material is one that incorporates graphite and cindered iron. The result is a friction material that offers good friction coefficient, torque capacity, and smoothness of engagement.
Carbon: Very high temperature material. Engagement is more abrupt. Will wear flywheel surface faster, especially in traffic situations. Slightly more durable and flywheel-friendly compared to other aggressive clutch materials. Material is black.
Sintered Iron: Extremely high temperature material. Engagement is extremely harsh and is generally considered an “on/off switch” both due to it’s characteristics and the clutch types this material is generally associated with. It requires a special flywheel surface. Material is metallic gray in color.
What is a dual friction clutch?
A dual friction clutch is when two different friction material facings are applied to each side of the clutch disk. For added performance and service life, Kevlar is added to the pressure plate side of the clutch disk and the other side remains organic. For street and strip, a dual friction disk is often a combo of Kevlar and metal. The one flaw in this logic is that your overall holding power is then limited to the weakest holding material.
Which clutch material is right for my car?
This depends on your configuration and the manufacturer's specifications. Each manufacturer has their own "recipe" for each clutch material type so that Manufacturer A's organic clutch material (for example) can be quite different from Manufacturer B's organic clutch material. Many clutch materials can be doped with other materials to provide different characteristics than would be expected of that particular type of clutch material. Changing to a more aggressive clutch material can gain increases of 10% to as high as 60% in the amount of torque they can hold.
As to the rating of clutches, most manufacturers rate their clutches to the point of slip, instead of being able to sustain long term use at specified ratings. Torque ratings are based off of the average torque per crank rotation, if you buy a clutch which is border line with the amount of torque you put out, chances are its going to start slipping sooner than later.
Do I need a sprung or unsprung clutch?
Many do not consider this an important issue. A sprung clutch allows it to act similarly to springs on a car. In this fashion, the clutch is “engaged”, slack is taken out of the springs, and then the clutch is fully engaged. The actual amount of travel of these springs in only a few millimeters. The theory is that the springs will dampen the engagement slightly and to soften driveline shock and reduce associated clutch engagement noise. To generalize, sprung clutches are preferred for street use and unsprung clutches are preferred for racing applications.
What causes increased clutch pedal pressure?
Pressure plate clamp force. Just because you buy an aftermarket clutch does not mean you have to have a heavy clutch pedal. The amount of increase over the OEM clutch pedal pressure is dependent upon what the pressure plate manufacturer's specifications are.
Are there any drawbacks to high clamping pressure plates?
Generally speaking, the higher clamping pressure of the pressure plate, the higher pressure you induce on your crankshaft thrust bearings.
What is the most transmission friendly clutch?
The OEM organic clutch is by far the easiest on your transmission. This is due to the lighter clamp loads of the OEM pressure plate and the organic clutch material. Organic materials, which are bound by resins, will almost always loose friction when they get very hot. This is because the resin melts and becomes almost like a lubricant rather than a bonding agent. Any increase in clamp load or clutch material coefficient of friction will increase the shock load to your gears.
What clutch will hold the most power?
Generally speaking, one that has:
a. Highly sprung pressure plate. The more clamping force the pressure plate exerts, the better it will grip.
b. High coefficient of friction clutch material. The higher the coefficient of friction, the better it will grip.
c. Increase the amount of surfaces. This can be accomplished by going to a twin or triple disc design.
What about a "Stage 1 clutch"?
Stage 1, 2, 3, etc. clutches are just a marketing tools. Some manufacturers have them, some don't. While a staged clutch may suit your application.
How hard is it to install a clutch?
Allow around five hours for install time. Professional installation, depending on your area, is around $300. This is one vehicle modification that should be farmed out to a professional unless you have the right tools/equipment and are mechanically skilled.
-----------------------------------------------------
Flywheels - Lightweight vs. Heavyweight
To answer the much heated and most debated question. Should i get a light, or should i stay with stock? Let me try to explain this as easily as possible and let you decide.
Rotating mass takes energy to spin it from one RPM to another. Therefore, it takes power from the engine that could otherwise be used to accelerate the vehicle.
The significant measure of rotating mass is called the mass moment of inertia. To keep it simple, weight is bad, but weight farther from the center-of-rotation is much worse. The mass moment of inertia is measured by the mass (weight) multiplied by the distance between the weight and center of rotation squared. For instance if you had a weight of 10 pounds mass, 5 inches from the center of rotation, its' mass moment of inertia would be 10 lb x 5 in x 5 in = 250 lb in^2. That same 10 pounds only one inch from the center of rotation would only have a mass moment of inertia of 10 lb in^2 (96% less). This is why lower diameter flywheels are an issue and heavy larger wheels can have an effect.
When you were a child you may remember playing on hand pushed marry-go-rounds. Kids would stand on them and other children push to get them spinning. You may also remember that it was much harder to push when there were more kids on the marry-go-round and they stood near the edges.
Now for the stock flywheel. I am told the stock flywheel has a mass moment of inertia of 280 lb in^2 and I used this value in these calculations. Let me warn, the effect of rotating mass is not constant for RPM or road speed. In other words, the effect in 1st gear is different than second, and in any gear the effect changes with speed. This is why, if anybody quotes a given horsepower savings measured on a dyno, it is not accurate because chassis dynos DO NOT simulate accurate transients. They measure horsepower at the wheels just fine, but they can not measure the effect of a lightened flywheel, tires, or wheels. They will measure a difference, it just isn't accurate. But it is easy to calculate the difference.
From simple calculations the stock flywheel (280 lb in^2) takes 10-20 HP to spin it while accelerating in 1st gear. In second gear it takes about 5 HP. In 3rd gear it takes 2-3 HP. Therefore, if your lightweight flywheel had half the stock flywheel mass moment of inertia, you could save half the above values. To me, this would be more significant in a 1/4 mile run where the launch and 1st gear is very important. On a road course, not as important.
You might wonder why 1st gear is so much larger? The most stock engines (B or D series) spins from idle to REV LIMIT in less than 4 seconds (give or take) in 1st gear. It takes a lot of power to spin this mass to high RPM very quickly. In 4th gear, the stock flywheel takes 10-20 seconds to go from MID to REV LIMIT RPM, therefore, much less power required.
A transmission can be thought of as a fulcrum and lever in a car. First gear has a really long lever; second gear has a shorter lever, etc. The lever represents the mechanical advantage that gears give your vehicle. When your car is moving, you have two factors that are present during acceleration, one is driveline losses, which are constant and the variable, which is vehicle weight and the mechanical advantage supplied by each gear. We know that within reason, vehicle mass is a constant. Now imagine if you reduced the driveline loss from 45 to 35 with the use of a lightweight flywheel. Since the engine has less drivetrain losses to compensate for, this means the "gained" horsepower can be applied to moving the vehicle mass. Using mathematics, one can realize that the higher you go up in gears, the less effect that a lightened flywheel will have to the overall equation.
While the performance characteristics of a lightweight flywheel seem to be the perfect solution, there are compromises. Low end performance is affected. This usually means that higher revs are necessary for smooth starts due to the reduced rotational mass. For drag racers, this can be a BIG issue.
-xproductionz.com
Last edited by xproductionz : 12-09-2006 at 11:52 AM.
|
