I bought a OEM clutch disk (996 116 013 51) to have as a spare. The hub is heavy and very well constructed but it's only about 9 1/4" diameter (235mm). This seems way too small for an engine with over 400 ft. lbs. torque. Most cars with similar - or less - torque have much larger disks. Anyone know the pressure plate clamping pressure? I guess this is why first gear is so short. Is there something special about these cutches that makes the small size adequate? I think I'll forget about ever going to the drag strip.

 

I dont know the answers to your qustions but I have noticed that it is very hard for me to quickly launch the car without bogging the engine or burning the clutch!

 

mbailey, it is for me too. I've had several times where I felt I was bogging the engine. Yuck.

ebaker, I think the reason it's not larger is 2 fold:
1) you don't have all that torque being applied to it while the clutch is hooking up generally because the Turbos aren't kicking in yet.
2) the smaller it is, the easier it is to rev the engine and turbos are generally more difficult to rev than NA (ie. rev matching or heel-toe)

 

Ruiner,
If I launch at 4000+ rpms I will burn the clutch and get very little traction. Is there something wrong with my clutch?

 

My understanding is that many manufaturers of AWD cars use a smaller than optimal clutch to act as fuse. Look at it this way, would you rather smoke the clutch? ...or break something in the drivetrain?

AWD cars have a lot of traction. It's not like you can sping the tires. Well at least not for very long.

 

I use a "small" disc. It is 5.5 inch, carbon/carbon, ultra high tension pressure plate. Mine has four discs. You can buy them with two, three or four discs. Mine will hold 1000 ft/lbs. torque and will hold 10,000 rpm's. It is also very easy and economical to rebuild. You can always measure how much life is left at any time. I have launched at 6000 rpm's with no problem and that is with a 3.17-1 ratio first gear. The clutch can also be bought with 7.25 inch discs. The clutch is made by Tilton. www.tiltonracing.com

 

My '78 928 had a dual disk about 8.5 inch clutch from the factory. It lasted 90,000 miles. It only took about 2 hours to replace, no major parts to remove, just slide back a coupling and drop it out. The later 928's had an 11" single disk clutch I believe.
I wonder if Tilton makes a streetable clutch? A dual disk 7.25" sounds good. I think Porsche racing makes the special flywheels for the Tilton's that drive up the cost.
I believe that wheel hop greatly increases the drivetrain loads.
With a stronger clutch what is the weak link? The transmission and rear CV joints seem strong. The fluid coupling should protect the front differential and driveshafts.

 

If Killer Angel has a weak link it is the CV joints. The differencial, driveline and transmission have all been addressed. To date, no problems.