ACT vs SPEC?
 

I have heard good and bad about both. I currently have a ACT street strip on my car. I am going to upgrade to either the ACT 6 puck sprung or the SPEC stage 2+. I need the added tq rating for my new turbo setup. I'm ordering tomorrow morning and am torn. Please give some advice/experience. I searched seems like Rich and Howard might know about the SPEC?

I basically want the most street able clutch that can handle 500tq.

Thanks.

Steve Prew

I have a spec 2+ in my fd, no problems at 450 hp.

thanks ryan. anyone else have an opinion?

clutches are like bananas.

you buy them by the pound.

that's foot-pounds ( i am old school, you can call it pound feet if you wish)

so you need a clutch that will hold 500 ft pounds of rear wheel torque. that's a different neighborhood that the poster above who is making 450 rwhp. he is making 340-360 rw torque. the exedy hyper single cerametallic would be good for him. a number of single discs would also work.

for you at 500 ft pounds and 620-660 rwhp, you will need a double disc.

there are a few options. i prefer Exedy's cerametallic double. it will hold 600 rear wheel ft pounds if you are road racing and 515 if you are drag racing. since it's frictional area is much larger than a single disc it doesn't need as much clamping pressure (2205 pounds) so it is easier on the pedal, your leg and the throwout bearing arm.

being the R&D arm of a multibillion dollar driveline parts (OEM for toyota, mazda, gm, ford etc) company the money has been spent on making it right. the cerametallic material, for example, is patented.

currently there is a 2500 mile Exedy ZM022SD (the one you want for an FD) for sale in the 3rd gen classifieds. look for a thread entitled "Engine etc on page 1 or 2 by Cloud9.

500 ft pounds = double disc.

BTW... carbon. has a coefficient of friction between .31 and .48 depending on heat, i don't like it for that reason as you can't depend on it. Exedy cerametallic has a .49 coefficient not dependent on heat. further, carbon and the metallic mating surfaces only coexist. many say that carbon clutches don't hold the torque. exedy rates it's carbon clutches 10% lower than cerametallic. carbon/carbon, as in Tilton, is another story but you'll need to bring a heavier wallet.

while a double disc is more cash, it is cheaper than buying a single, trashing it and then buying the double.

good luck,

howard coleman

Hi Howard,

I think the most important factor is the pressure plate clamp load. Years ago someone at ACT told me that pressure plate clamp load is primarily what determines torque capacity.
ACT and Carbonetics both use higher clamp loads than Exedy for their carbon clutches and claim they are less temperature sensitive as a result. I asked Exedy why they don't offer a stiffer pressure plate diaphragm for their clutches and they said it makes the clutch pedal resistance curve less progressive; with a stiffer diaphragm the force required to move the pedal early on in the arc is significantly higher for an incremental gain in clamp load. This level of refinement is less of a concern in the domestic world (and probably here) where ACT seems to make its livelihood and single disk clutches that hold 500lbft are not unheard of. If you surf the corvette boards you will find that it is not just the carbon Exedy clutches that people have problems with on high torque motors but their non carbon multi-disk setups as well.

I think friction coefficient also plays a roll, but to a much lesser degree. I agree that carbon varies more than other materials, but I have yet to see a disk material that does not change based on temperature. Someone at Tilton told me that the friction coefficient of the non carbon intermediates plates goes DOWN as they heat up. I would think that this would to some degree mitigate the increase in friction coefficient of the carbon disks to create a more consistent feel than the raw data would suggest. In any event ACT and Carbonetics both test the torque capacity of their carbon clutches cold as well.

-FWIW

you say clamp load is the most important factor re torque?


exedy hyper single w 2655 pounds of clamp holds 395 RW ft pounds

exedy hyper twin w 2205 pounds of clamp holds 599 RW ft pounds

think frictional area.


as to all FD single discs....

there's only so much you can do w the physics of the situation. we are limited to a 225 mm diameter. you only have so much frictional area so you up the clamp to up the torque. at a certain point you end up at the end of your rope. as the ACT tech guy (daryl) i talked to said at around 500 foot pounds of torque at the flywheel, 425 ft pounds at the rear wheels, you have just made your car into something you will hate to drive on the street while at the same time overstressing the clutch throwout arm.

no thanks.

i want to enjoy driving my car so i will take the double disc.

ACT uses higher clamp than Exedy because they have less frictional surface and they are trying to make their single work like Exedy's double. they are coming out w a double disc soon but not for the FD.

Carbonetic uses 3520 clamp on their single and 2420 on their twin here again making the point that frictional area matters. they have no immediate plans to offer a pull clutch for the fd so you are stuck w running some kind of converter.

notice the higher clamp pressures for carbon due to lower friction coefficient.

another issue w carbon is break in. if you don't do it right you will be unhappy w your clutch. almost all of the problems w carbon clutches relate to break in.

howard coleman

Hey Howard,

Thanks for the response. I should have been more clear in my original post. I need something that is rated about 500 ft/lbs at the crank. I have not looked into the double discs much, do you think that would be overkill for this setup? I plan to make between 500 and 600WHP and the torque to match.

Thanks,

Steve

Obviously that's true and why the Exedy Comp R clutches are rated to a lower torque capacity than the standard clutches (200mm v 215mm I believe). But within the context of a discussion about carbon vs. non carbon clutches with the same surface area I believe clamp load is a more significant factor than the disk friction coefficient.

This is a matter of individual preference. Preference might be the wrong word -tolerance might be a better one.

The benefit to multi disk setups to me is
1. their ultimate torque capacity
2. their torque capacity relative to pedal pressure
The drawbacks are
1. Noise/chatter -a lot of people complain about noise at idle, gear change, and decel to varying degrees.
2. Higher ingoing cost and disk replacement cost.
3. Weight –Instead of 1 disk a twinplate clutch as two disks, an intermediate ‘floating plate’ and a center hub to hold the whole mess together.

#3 is very important to me. In an ideal world I would like a 6 liter car engine with the rotating inertia of a sport bike. This is why I think a carbon multiplate setup with a relatively high clamp load provides the best of both worlds for my application. The multi disk layout has a lot of surface area, the carbon disks negate most of the weight gain over a non-carbon single disk setup and the stiffer pressure plate offsets the drop in the lower cold friction coefficient. That leaves cost as the main downside, and I’ve gave up on winning that battle a long time ago. For those that don’t need quite as much torque capacity and can tolerate a stiffer clutch pedal, I think a single disk clutch with a light flywheel and a stronger pressure plate might be a better choice than an Exedy multi plate setup, especially when cost is factored in.

That's my thinking as well. But if you will be making considerable torque, a twin plate is the way to go. I prefer the Exedy D-Core simply b/c it's the most streetable twin plate, given that essentially any twin plate *will* get the job done; it only becomes a matter of how (streetability).

If you have the nice large cash flow, however, Tilton, has, still is, and prob will always be the way to go ;)

That's my $0.02,
~Ramy

For the 2 rotor guys using pump gas you're probably right -any twinplate will do. However, if you move to the next level, you still have to consider torque capacity. Read the Supra and Corvette forums. A lot of people have had problems with Exedy clutches slipping on high torque applications. There is a post in the 20b section discussing this very issue with the D-core right now. Obviously setup and break-in are also factors, but based on what I have read here and in other places I tend to think that Exedy is too liberal with their torque ratings.
Believe me, I'm all for streetability. But if you're after big power numbers I think compromises must be made. Again, I think greater emphasis should be placed on the pressure plate.


"Exedy d-core keeps slipping during highway pulls

--------------------------------------------------------------------------------

Not sure if Im not warming up the clutch enough or it cant hold the power, but my exedy twin plate carbon keeps slipping during 4th gear pulls.

It did this on the dyno @ seven stock as well, it getting really annoying.

Might be a stupid question, but what ist eh proper way to warm up this type of clutch?

Thanks"

https://www.rx7club.com/20b-forum-95/exedy-d-core-keeps-slipping-during-highway-pulls-641753/

This thread is real hard for a clutch noob like myself to follow. I really do need to decide on a clutch though. Like I said before I would like something rated around 500ft/lbs at the crank.

From what I understand you guys are saying that if I could afford a dual disc it may be overkill but just as streetable as a single disc with a stiff pressure plate?

I am looking to spend $1000 or less so I'm not sure what that leaves me.

I would call all the companies we have discussed above yourself. I think a Spec 3+ would be a good choice.

I had a spec stage III clutch and had a horrible experience with it. I managed to put about 12k miles on it (untracked) and during normal driving it popped one of the springs out of the pressure plate. Not a well designed clutch. Catch point would move around. It was real chattery. Not what I was expecting out of a sprung clutch.

I replaced it with a 6puck ACT and couldnt have been happier. Consistant catch point, not anywhere close to as chattery. A lot smoother. And it looks like a much better engineered piece of equipment.


Ive worked at a tuner shop and talked to a lot of people who've had spec clutchs and had them fail on them (most actually had the spring pop out like me. others had it break the pressure plate in various locations). The Spec gripped alright, but in terms of durability, it was far inferior. Ive driven a 3puck solid I installed on a built CRX and I personally found it more driveable than my spec ever was. There's something not right with that. Maybe the stage II is designed better than my stage III, but I personaly wouldnt ever buy from Spec again (especially after the customer service was an asshole with me and told me it was my fault) and I sure wont let any of my friends buy a spec clutch. Most saw what happened to mine, though, and realized how poorly designed it was.

I'm running this clutch now and am very happy with it. It's handled the 500R throughout a fourth gear pull at 19 psi with no problems, so I think it'll make your 500 ft/lb motor torque stipulation.

I've also had great experiences with the ACT street/strip (stock disc, hd pp). It last for many years and over 50k miles. The new sprung ACT 6 puck wouldnt be a bad way to go either.

Rich how would you compare the stage 3 to the street/strip as far as pedal feel? I have the ACT now and am worried about making the car less streetable.

The Spec requires much less pedal effort than my old ACT HD-00 (street/strip). It's 100% streetable, but so was the ACT. Keep in mind I upgraded from a stock disc (ACT) to a sprung 6 puck (spec).

Oh ok. So you ran the stage 3 6 puck. The 3+ is a full disc that claims it can handle 600ft/lbs? This stage x and x+ shit is annoying. I am not sure whether to get the 2+ = 500ft/lbs or 3+ = 600ft/lbs.

reviews on spec often seem mixed. i am happy that Rich has had a good experience.

i have great regard for ACT and note that their Heavy Duty pressure plate w either a 4 or 6 pad disc rates at 514 flywheel torque.

the Xtreme (consider the word carefully) w the 4 puck is rated at 577 and the 6 pad is rated at 514 FW Torque. the head tech guy at ACT told me the Xtreme is, well, extreme on the street. re-enforce your pedal.

if you were to do ACT you'd go w the Heavy Duty pp and a 6 puck...

the Spec lineup is rated at 518 for the 3 and 598 for the 3+ flywheel. i do wonder about the 598 number.

given your budget the ACT looks like the ticket.

hc

This would be the ACT...514ft/lbs

http://www.rx7store.net/product_p/zx3-hdg6.htm

Would I need to order it special with a heavy duty pressure plate?

OR

SPEC Stage 3...518ft/lbs

https://www.rx7club.com/attachment.p...d=231960&stc=1

OR

SPEC Stage 2+...495ft/lbs

https://www.rx7club.com/attachment.p...d=231959&stc=1


Heres the different SPECs
https://www.rx7club.com/attachment.p...d=231958&stc=1


Would the spec 2+ be more streetable because it is a full disc or does this not play a part?

yes, that would be my choice if you go ACT. along w the correct ACT flywheel... and they are nice. chrome moly wheels generally don't take off your feet like aluminum do.

hc

6 puck is no fun to drive on the street. That thing seriously is a pain in the ass.

The twin and triple plate clutches retain the stock feel making it much more enjoyable to drive...

^I agree I have a six puck SPEC stage 3 in my daily car, and it is a pain, good clutch though. I put in it a few years ago thinking I would turbo charge the car at some point but decide an FD was a better option. Pedal is basically the same feel as stock except for the engagement point being about 1/2cm wide, either engaged or not pretty much. Very chattery/bouncy when you ease out on it.

Absolutely. But then again, w/ the torque #s some guys are making, they're flirting w/ the limit of the clutch they're using. In some cases, they really need to be running a triple plate. There's *nothing* wrong w/ getting a clutch stronger than your application; in fact, it'll simply grab better and last longer.

Also, like you alluded to, diff. companies rate their clutch torque ratings differently. From my convo w/ the Chief Engineer @ Tilton, IIRC, they rate their clutch torque ratings at FIFTY PERCENT of the max torque they handled when they began to slip. That's HUGELY underrating them. But that's also one of the reasons why when you purchase the PROPER Tilton clutch, you're pretty much set.

Just to qualify this statement Rich...you haven't exactly been making that kind of power for long, have ya? So it's a wee bit early to pass any judgment on that clutch's ability IMO. How LONG it'll hold such pulls is the real question ;)

Ditto. But the max rating on the HD one is like 420 ft lbs of torque IIRC.

Sprung will undoubtedly be much more streetable than an unsprung clutch, but on the full spectrum of streetable and unstreetable clutches, non-disc clutches (ie 4 and 6 puck clutches) are considerably over on the non-streetable side ;) You getting "used" to the clutch crappy engagement doesn't constitute streetability, Rich :p:

~Ramy

Well, I've put ~500 miles of hard driving on the clutch with my 500R at 15+ psi and it hasn't skipped a beat. I agree though, this is acecdotal and should be taken with a grain of salt.

Re: streetability, I have driven many many FDs (over 100 at this point) and agree that unsprung 6 pucks are horrid. This particular sprung 6 puck is very manageable on the street, however. Daily drivability without a doubt :icon_tup:

A couple of things to keep in mind with respect to the foregoing arguments:

It should be clarified that it's clamp load per unit area that matters. Increasing the area of a single disc will reduce the unit area loading, and theoretically, will make no difference in the torque capacity of the clutch. In reality, additional area will marginally increase the holding ability of the clutch (once you've exceeded a certain critical minimum area). What more surface area does is allow a longer service life for a single disc. Therefore, clamp load is arguably the most important factor for a single disc's holding ability. COF is going to be number 2.

Adding a second disc in a multiplate clutch allows you to increase the frictional area while maintaining the unit area loading because each disc sees the full clamp load. In this sense, composite frictional area is at least as important as clamp load since you can vary the holding ability of the clutch in proportion to the number of discs that are employed. Or, you can maintain a certain torque capacity and reduce the amount of clamp load as has been pointed out elsewhere.