Carl Fausett

Lil' help from fellow Sharksters - I have put 3 clutches in my Supercharged 928 this summer. I raced at Blackhawk this weekend and destroyed my clutch in a lap and a half. It slips like nuts. I use the stock twin-disk setup and have already machined the flywheel, replaced the intermediate plate, pressure plate, throwout bearing, pilot bearing, throwout bearing center tube, you-name-it. I did get oil on it once before, but that is no longer the case. This clutch is clean and dry and oil-free, and when I desassemble it, the pressure plate and intermediate plate is blue from heat. The stock twin-disk setup is supposed to handle up to 450 HP, I am told, but I am really starting to question that. I am supposed to be at 412 HP myself right now according to the engine dyno SOFTWARE I use, but I have not been to a dyno yet to find out for real cuz my clutch keeps slipping! No sense going to a dyno untill I get this slipping clutch thing solved.

Does ANYBODY know where I can find a stronger pressure plate and disk setup for the 928?

Any help appreciated.

Fastest928

We all run over 450 rwhp/rqtq through a stock 2 dsic setup...Torque, not hp is what you need to know to decide if a clutch will hole..the only possibility is either you are:

making more torque than above
or, the int plate was machined and its thickness reduced!

Dyno your car on a dynojet and see what you really have...you never know, maybe just a bit more/less fuel and you will have another 100 hp!!!???

Marc
DEVEK

vicente

<a href="http://www.projekt928.com/928_Performance_Parts.html" target="_blank">http://www.projekt928.com/928_Performance_Parts.html</a>

Im also thinking about a stronger clutch like the one shown on this link. Im only worried about the "feel". Im told "exotic" clutches are very rough.

Comments anyone?

Carl Fausett

Thanks Marc - but my intermediate plate is NEW and must have the right thickness. Flywheel surfacing has been nominal, just to gice it a surface. Are the SACHS friction disks "soft" ? That is what I am using - is there somthing tougher out there? Three friction disk pairs in 3 months is no fun.

John..

I run a bone stock twin disk on my Callaway 928. It makes about 400 HP at the crank, and I have had no problems with slipping. Callaway originally installed resurfaced sintered metal disks on the car back in 1983. They were junk, and completely destroyed the pressure plate and intermediate plate. I went with the stock clutch (against Callaways recommendation) and have yet to have any problems. That was 2 years ago.

Maybe you could investigate getting special springs made for the pressure plate, or go with a slightly different friction surface? There are lots of places resurfacing clutches, so take a couple of your old disks and have a different material riveted on.....just make sure the stack height is correct, or it won't work for crap.

I have heard that kevlar disks are supposed to be more durable, but I really don't have any experience there. Unless you are running over 10 psig of boost, I highly doubt the car makes over 425-450 HP. I run 8.5 psig of manifold pressure and mine comes in somewhere between 375 and 400 HP depending on ambient temperatures. Of course I don't know if you have done any internal mods, so anything is possible.

Carl Fausett

That's good advise, John. I'll look into that. I have also heard of removing some material off the pressure plate fulcrums to increase the clamping force. Does anybody have experience with that?

Carlos

Carl, I'm with you. I don't have that much faith in the stock set up. If they were so great you wouldn't have all the aftermarket stuff for 911's & 944's. Next the blower and the turbo are totally different. The blower comes on harder down low, especially if it's a Vortec. Also driving style can place totally different demands on a clutch. Mine is getting due and i've been looking. The best i've come up with is rebuilding the old plate & disk. Try clutch masters. They might have something for you.

Carl Fausett

I just found out all 928 twin-disk clutches are not created equal... apparantly the 78/79 twin-disk clutch was changed in the 80-85 model years to provide more clamping force. Ther guys at FAST in TX say that the 80-85 twin disk clutch setup is a bolt-in swap for the early cars like mine, and will handle up to 550 HP. I'm going there and have all the parts coming from Mark Anderson. The release fork and bearing are the same, but I have to replace my flywheel, intermediate plate, pressure plate, and disks. I will try to report my results.