Clutches

I have always been a firm believer in multi-plate clutches, but of course it will always depend on the application. I noticed there seems to be a general lack of clutch knowledge. Here’s a quick primer on clutch selection in the form of some Q&A’s:

1. How high of an RPM will you be turning the engine?
OEM style factory replacement high performance clutches do have their place. Generally, OEM style stamped steel cover clutches are designed for just that: OEM applications. They are heavy, flexible, and are manufactured less precisely with larger tolerances. Because they are flexible, heavy, and tend to disengage slowly, they usually cannot slow the input shaft down fast enough for you to slam the next gear. What happens? You grind gears and break clutch parts because of this. Lightweight, unsprung hub copper discs can help in this department, but you will often get chatter and super small engagement point which makes street driving a bitch. Clutch companies modify the fulcrum point of the diaphragm to increase leverage. This creates a higher pressure for less pedal effort, but then the stamped steel cover starts to flex more. If your engine is going to be making slightly more power, but with only a minor increase in RPM, then an OEM style replacement high performance clutch is probably ok for you. For the OEM style factory replacement high performance clutches, I always use ACT clutches. Dirk makes the best OEM style clutches hands down.

2. I will be turning 9000rpm, but my stock redline is 7000rpm. Will an OEM style replacement clutch work for me?
The short answer is no. Don’t be a fucking tight ass. If you spent the money to be making power up at 9000rpm, you’ve obviously spent some serious money. Get yourself an HKS, OS Giken, Exedy, or Tilton (if you can afford one).

3. The clutch company says their clutch will handle 850whp. Everybody’s doing it, why can’t I?
Just because Tom jumps off the bridge doesn’t mean you should too. The simple reality is that OEM style high performance clutches just are not designed for this kind of power. See pictures below of a failure due to high power and high rpm. Don’t believe the hype people.

4. Why is a multi-plate clutch better?
Multiple plates mean more friction surfaces. A twin plate has twice the friction, a triple plate has triple the friction, and so on. This huge increase in friction is with minimal expense in pedal pressure also. Remember the last time you drove your buddy’s Supra with the double throwdown 3600lb pressure plate? Did you also notice your buddy’s Popeye left leg? Sure, the clutch grabs harder, but your left calf is fucked, the cover is flexing, the hydraulics will fail sooner, the thrust bearings in the engine can fail sooner, etc. There’s nothing but negatives. Don’t be a fucking tight ass and get a multi-plate please.

5. V-8 guys have been running stamped steel covers with 800ft-lbs of torque for the last 30 years! You’re full of shit. Why should I listen to you?
Don’t listen to me you dumb pile of shit. Built V-8’s have relatively low redlines compared to small ass Japanese engines. A hot small block revs to what, 7000rpm? A hot big block revs to maybe 6000rpm? Even the V-8 guys who rev high are smart and either get multi-plates, automatics, or planetary geared drag transmissions like a Lenco and they use slipper clutches. It’s rare for high power, high revving V-8’s outside of NASCAR to run manual transmissions because most of them are drag fanatics. And guess what kind of clutch NASCARs run? You got it: multi-plates.

6. Why do they seem to only have multi-plate clutches for heavier 4WD cars?
This one’s pretty obvious: because it’s harder on the clutch. With a Skyline GT-R that weighs 3600lbs and makes 600whp, try dropping the clutch at 8000rpm next time and tell me what happens to your SPEC brand OEM style clutch? You got it: you’ll fry the living shit out of it if you don’t break something else shifting. The new generation of heavy 4WD cars like the STI, EVO, and GT-Rs (ex. R35) will require multi-plate clutches if you want any serious results.

rpsclutch1.jpg
Before 8200rpm and 800whp. See that thin ass strap trying to hold the stamped steel cover to that big ass piece of iron? There are only 3 of those mass produced, manufactured by some 60 year old grandma in some desolate factory town in some third world country standing in front of a giant hydraulic press that is trying to keep things together. Mass production and old ladies equal only mediocre quality control. That’s ok for 260whp though.

rpsclutch2.jpg
What happened to grandma’s strap? After two shifts at 8200rpm and 800whp a rivet gave up and/or the strap failed. I’m not going to mention any brand names though. You can see that the transmission case is cracked. It’s a fucking damn good thing that pieces of clutch and flywheel didn’t go through the trans case, floor pan and chop off my fucking legs.

Generally, I’d say an OEM style replacement clutch is good for about +100whp and another 500rpm beyond factory redline and that’s even pushing it a bit. Anything beyond this kind of power or RPM, get a multi-plate and save yourself a transmission, left calf, engine, hydraulics, and/or even maybe a leg. Remember high quality car parts are not cheap. Be sure to always pick the right part for the job even if it costs you an arm and a leg (pun not intended).

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