I'm going to have to buy a new clutch over the winter, and am looking for some suggestions on the best cost/quality clutch that will hold approx 350-390 awhp.

ACT 2100 and ACT Street Disk or a 6 puck disk

350 awhp is over 400 at the crank.
You'll want a 2600 if you do not want to push its limits and possibly have it slip.

I am inclined to agree. If you are REALLY going to be making that kind of power, go 2600.

I was thinking 26 or 2900 if I went ACT... but that's what I wanted to find out. If ACT was the best bang for our buck. This is just a weekend warrior car. Probably won't be touched during the week and will be mostly for playing around. Don't anticipate many hard launches or anything.

I would say Bully Stage 3 6-puck w/ceramic buttons...ceramic/kevlar if you drive it more on the street. I like being able to send my disc back to Bully (Ottawa) to get new friction material put on when it eventually wears out.

Im approaching/close to the power range you want and I recently just put in a 6 puck with my old 2100 ACT PP, As my street disk wore out within a year (slipped the clutch way too much one day and fried it)

I drive my car hard and do the occassional launch on the back roads, I have no complaints with the 6 puck other than the chatter intially. The 6 puck will also hold more power than the street disk.

I think Helber ran an 11."6" on an ACT 2100....

The pressure plate does all the "holding". and the disks do the "gripping"

Correct me if I am wrong, but I dont see how a 6 puck can "hold" that much more power than a street disk. Thats what the pressure plate does.

Well a pucked disk does hold more power. It's the same force from the pressure plate on less of a surface area.

2600 + Street Disc = Fun, reliable, simple.

You could also go CFDF.

It has nothing to do with surface area. The 6 pucks generally have a higher friction coefficient which means the same clamping force generates more torque capacity.

I have a 6 puck/2100 I've been happy so far (I find it shifts really well at high RPM, probably due to the lower rotating inertia) but I'm not quite to your power levels yet.

How do you think they get that higher coefficient of friction? Less surface area means that same clamping force is spread out over a smaller area, resulting in higher force (friction) in those areas.

This was the general train of thought. Am I 100% sure I'm correct? Nope but it seems to make perfect sense to me.

I run an old RPS 2500 clutch with a Eurodrive sprung 6-puck. Drive like any 2600 with street disk and holds up to 132MPH in the 1/4 mile. In case you can't relate, the car is BOOOOGYING.

Sure is.... hopefully you can run that 40 psi at the track this year an crack off the high 10 you want on your street tires!

Don't want to turn this in to an argumentative thread, doesn't help the OP, but you are just plain wrong . Coefficient of friction has nothing to do with surface area (well for the general case anyway, softer materials and/or extreme pressures change the picture).

The material that they make race clutches out of is different. The material has a higher frcition coefficient (at any surface area), and usually a higher stength and heat tolerance as well. The higher strength and heat tolerance combined with the higher coefficient of friction allow them to use a smaller amount of material, which makes it lighter and cool better.

Not argumentative at all. It's informative, and Tim and I are following a line of thought, be it correct or not.

1) Wouldn't it be even better if they made a full disc out of this 'better-gripping' material? (Not saying they don't have better material, they probably do.)

2) If you have a 200lb fridge, and a 200lb waterbed, isn't it more likely the fridge will go through the floor because the pressure is exerted over a smaller area? Doesn't this equate to a greater clamping force in that area, like the calipers of your disc brakes closing?

But, puck or no - the force is still spread out over the exact same area, because the diameter of the input shaft does not change!!!

I agree with Bradley: It's the material and the cooling that makes a puck not suck.

1. Pressure = Force / Area. If you have the same pressure source (pressure plate) and you reduce the area that it is applied to (full face vs. 6-puck), the normal force (perpindicular to the surface) increases.

2. Friction force = Coefficient of Friction * Normal force

3. Increase in normal force = increase in friction force.

4. Surface area has no bearing on the co-efficient of friction. Surface area does increase the effective friction force due to mechanical reasons between the mating surfaces on a microscopic surface level. If you apply the same normal force on 1 m^2 or 10 m^2, the friction force will be theoretically the same.

So in the end...

A 2100 and a pucked disk will not meet his 400hp/tq needs?

That's not right. You wouldn't model the pressure plate surface as a pressure source in an FEA. You'd model it as a rigid body transferring the force from the springs in the pressure plate assembly.

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The ACT website used to have a 'university' section on this type of topic. Also, they list the exact amount of torque every combination would produce.

From ACT's website:
ACT 2100 (HD) + Organic Disk = 322 lb-ft
ACT 2100 (HD) + Six Puck = 412 lb-ft

http://www.advancedclutch.com/products/clutchkits.aspx?prod_id=2119#2119

True. The correct way to say it would've been pressure plate force. I didn't think it would matter in terms of explaining the concept on a car forum since the part is called the 'pressure plate'.


Are those ACT numbers at the wheel or crank?

Engineers, help me to understand...

Wouldn't a 6-puck simply transfer the same amount of pressure plate force on to less of the flywheel's surface area (when compared to a full face disc)?
In my feeble mind, this would net less grip (with the materials being equal).
If it were the other way around, then why would anyone run wide tires or slicks at the track? Isn't it the same principle?

Consider the top of a pizza box as your pressure plate. The top of the box exerts a force of 1000lbs on the pizza underneath it.

If that pizza is a 20 slice, that 1000lbs of force is shared equally among the slices. Each slice will support 50lbs of force, and given a co-efficient of friction of 0.5 will provide 25lbs for friction force.

If that pizza is a 10 slice, that 1000lbs of force is shared equally among 10 slices instead of 20. Each slice will support 100lbs of force, and given a co-efficient of friction of 0.5 will provice 50lbs of friction force.

This assumes the each pizza slice is the same surface area regardless of being a 20 or 10 slicer. The 20 slice pizza has more surface area than the 10 slicer.

The pressure plate can only supply a fixed amount of clamping force. The smaller the area that you spread that clamping force over, the higher the normal force on the disc.

That might've been a bad analogy but I'm hungry.

Is that why they put the little white plastic thing in the middle of the pizza box?



But didn't both pizza discs get 500lbs in the end?
So where's the advantage?

A wide slick or tire when heated up will grib better. A full face disk when heated up will slip. Two different things.

Obviously a 6 puck clutch provides better cooling, better friction, and each puck has more pressure applied to it from the pressure plate which makes it grib better, and dig into the pp/flywheel better, which cause it not to slip and bite hard.

Nothing to debate over, all three things make a puck clutch better: friction, better cooling, and better bite because of the extra pressure being applied to each puck.

Obviously friction alone cant hold the torque, so there is pressure needed. I think a balance of all three of these things are there.

Yeah I guess the tire was not the best analogy. My bad.

My problem with understanding (the grab/bite part alone) is that when I think of the disc I am considering the entire disc, and regardless of pucks or full face, the disc itself is getting the same pressure from the plate.

Oh well, I treid.
"For whatever reason, it just works."

So what makes a 3 puck clutch grip better than a 6 puck ?

Anyone care to explain that

Please, someone. And don't you dare just say it's because each puck gets more pressure.

I wonder if there is even a better friction (material) coefficent on the 3 puck than a 6 puck ???

The way I think of it is with snow tires compared to all seasons.

Snow tires generally have a thinner profile. This exerts more force on a smaller surface area and does not allow the car to slide on the snow, but rather cut through it. It's the same overall weight but it digs into the snow rather then floating on it.

The slippage of the clutch occurs between the flywheel and the disk or the plate and the disk. The best way to combat that is to decrease the surface area and exert a higher force on the flywheel. To do this, decrease the contact area and that will in turn, exert more force on the plate.

The total overall force is the same but the pressure from the plate to the flywheel is greater.

It's been years since I was in school and doing this type of calculations but I think I'm right?!

I have to learn to stay out of these friction discussions! I've had long discussions about rubber compounds with coefficients of friction greater than 1.

Rob's right. The theoretical friction force would be the same given the same clamping force.

This conversation goes on and on.

Since coefficient of friction is determined empirically, my position has been that it increases with the increase of normal force due to the interaction between the materials. I.e., the coeff of the puck material is 0.5 with 100lb load and with a 500lb load it would be 0.6.

Debate away...this is fun.

//edit - can we trust that the kevlar on a full face is the same manufacturing process construction as the kevlar on the 6-puck?

As for the tire contact patch - given the same weight and same air pressure in the tires, the contact patch area is the same with a 195 and 245 width tire. The profile changes from long and skinny to short and fat but the contact area is the same....I have to get back to work.

So does a 3 puck clutch have better material than a 6 puck ?
If so then I'll buy the friction thingy/concept.

No. At least not at Eurodrive. I posed that question a while ago to the builder at Eurodrive clutches and he BELIEVES its all the same material.

But you know what, who gives a f*ck. My SPRUNG 6-puck holds way more power than my street disk ever did.

Yeah. Physics sucks.

I'm sure you understand the whole lb/in.sq thing so no analogies to lying on a bed of nails versus only a few nails have to be drawn. It's been established that the force is exerted on a smaller area, it only needs to be proven why the lateral forces increase if the coefficient of friction remains the same.

Actually, I just thought of a better analogy. Think back on where I mentioned the waterbed and the fridge, each weighing the same, but with the fridge having less contact area with the ground. Isn't it easier to slide the waterbed around than the fridge? Or how disc brakes work. At some point, it's not how hard the material is clamping, but how well heat can be removed from the system...

I think Tim has the right answer and I'm sorry for opening this can of worms...
"who gives a f*ck"

It's the co-efficient of friction that makes it handle more torque.

If the reason a pucked disc held more torque than a full-face one was because it dug into the pressure plate, then that pressure plate would be warping under load. You'd have serious problems to worry about!

A full-face disc, usually organic, is fine for street use as it engages easily and does not chatter. However, its moment of inertia is high and that makes the input shaft take a long time to adjust its speed for the next gear.

One solution to reducing the moment of inertia is to simply cut away some material to resemble a puck type disc. However, this would cause the modified organic disc to lose heat handling capacity, since less material would heat up more easily.

Therefore, to reduce the moment of inertia and solve the heat problem, a puck type disc is used where the pucks are made of a material capable of handling higher heat, e.g. copper.

Puck-type discs usually end up on race cars with higher performing engines, so a higher torque capacity is desired. The softer organic materials don't offer sufficient friction to satisfy this need.

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Here's another link from ACT http://www.advancedclutch.com/products/racediscs.aspx

Look at bullet "09" where they talk about higher co-efficients of friction with ceramic materials.

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For the wider tire analogy to work, the clutch disc diameter would have to increase to hold more torque. However, this would require major changes, and in the end the gear shifts would be much slower.

Assuming 20% drivetrain losses:
350 AWHP to 390 AWHP = 420 Crank HP to 468 Crank HP

Given that our motors usually produce numerically less torque than horsepower, it's probably fair to expect less than 420 lb-ft to 468 lb-ft of torque.

You've mentioned that you'd only drive the car on weekends, but likely wouldn't race it much.

Most Likely Case Scenario --> Crank torque = 375 lb-ft torque
Option 1M: 2600 Pressure Plate (XT) + Organic Disc
Option 2M: 2100 Pressure Plate (HD) + 4 puck sprung or 6 puck sprung

Worst Case Scenario --> Crank torque = 468 lb-ft torque
Option 1W: 2600 Pressure Plate (XT) + 4 puck sprung or 6 puck sprung
(As per the ACT info, organic doesn't cut it for 468 lb-ft, but you might get away with it for a while, for various reasons.)

I picked up a Fidanza 4.3 which is a sprung 6 puck ceramic disk. Heard some good reviews & know a few guys that are marking around the 500awhp mark with them & their holding up great (yes I know clutches should be rated for torque no hp).

Personally I think its a combination of both the friction material & clamping area that determines the actual holding power of the clutch.

As mentioned above the CFDF probably won't be a good choice in this case. It won't take the abuse of those kinds of power levels in an awd car. Now if the OP was fwd, it would be a great choice.

Thank you Greg, that was heroic!


I don't think this one is so great because the bottom of the fridge and water bed are not clutch friction material, and they are probably not on a metal floor either

Who the frack would want to slide a water bed around? And fridges have rollers.

I personally think it's because in every puck setup, there's a little Chuck Norris in the friction material, and he round-house kicks the pressure plate into turning with the disc.

Look, I'm not making this stuff up, right out of text books. The problem with your waterbed analogy is that water beds way around 10x what a fridge does, so ofcourse it is harder to move.

As Tashko said, there will be a small change in friction coefficent due to pressure. For a stiff material like is used in ceramic based clutches it is almost 0 change, for a soft material like tires it is more pronounced due to mechanical interlocking(but still would not make the difference between 300 and 500ft-lbs). Either way if you don't accept it I'm taking my ball and going home:)

I agree that it's probably a combination of things, and I also incline towards Tim's way of thinking.

Heh, you guys sound like my wife when I'm trying to explain something to her...

"You see, hon. Life is like a box of chocolates...You never,"
"What are you talking about chocolates for? I wasn't talking about chocolates!"
"I'm trying to make an analogy so that you can understand it. In a box of chocolates the choices seem to always change..."
"You keep going on about chocolates! You're making me hungry! Do you have any chocolates? I'd kill for one right now."
*Sigh*