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spuggy spuggy is offline
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Join Date: Jul 2003
Location: Glorious Pac NW
Posts: 2,978
Quote:
Originally Posted by IROC 912 View Post
Aside from quattrorunner's clutch experiences with a 915 above, what type of clutch / PP system are others on this thread running ?

I have a slipping clutch (stock + carrera 3.2 PP) that I have to deal with this winter, but not keen on blowing up my mostly stock mag 7:31 915 with upgraded diff side cover. My end goal is a G50/01 that I have but still a long way off from collecting parts.

Any thoughts on this ? Most of these builds seem to be in the 300 - 350 hp range.

Cheers,

Sandeep
Sachs 915 "Power Kit" is a stock clutch cherry-picked off the line for top 10% of holding power. It'll seem OK with RoW power levels (930/60 == 300 HP) or slightly modified (+SC cams & open exhaust == +10%), but you'll have a service life of ~12-15,000 miles on a friction plate - e.g. you'll find to your surprise that you're down to the rivets when you drop to address something else.

I believe it actually slips at these power levels (hence the premature wear), but not so badly it's obvious and you notice.

Increase power significantly (e.g. bigger intercooler, K27/HF, headers), you'll be in the ballpark of 370 HP, 350 ft/lbs at the wheels - and a car that responds progressively to throttle - e.g. makes boost below 3000 RPM, like 6PSI @ 2400, given load.

You can't even progressively break the motor in with a (new) Power Kit at these levels - it'll very obviously break free and begin polishing the flywheel (e.g. it'll just get worse, and very quickly too) at any more than half-throttle in boost around max torque.

The good news is that a kevlar 6-puck clutch and an Sachs "Competition" RSR-style pressure plate will hold these power levels just fine.

There is, however, downside. Firstly, the increased spring/clamping pressure broke, one-by-one, break every aged part on the outside of the gearbox; actuating arm, bracket that holds the cable etc. - Save yourself the trouble and just replace them off the bat. I got pretty tired of hearing "huh, never seen one fail like that before"....

The puck clutch wants to be in or out. It'll complain/chatter loudly on hill starts or reversing up your sloped driveway, or anytime you're forced to slip it for more than 18" or so...

Stock 915 clutch, you can depress the pedal fully with one hand while lying with your head under the dash (e.g. at an awkward angle).

Competition PP? Ha. Nope.

The pressure plate will feel like a leg press after about 10 minutes in stop-go traffic, after which time you'll start to become seriously concerned as to whether you can continue to provide the finesse needed to slip the puck clutch, your leg will be shaking so much. After 20 minutes, you'll be audibly cursing.

The stock(-ish) 930/60 ate, chewed up and spat out my original '77 mag gearbox. The 5th gearset was dark blue, spun bearings, a real mess inside. Seemed no point rebuilding it - pretty clearly not up to the task.

A 7:31 C&P with a mag box and a 930 (or equivalent power/torque levels) really seems to be pushing the envelope a bit to me, as the 7:31 isn't considered advisable with a 3.0 SC...

I went with an '86 915, plate-type LSD (also a strengthening factor), WEVO bearing plate, factory cooler pump and internal oil bars, new bearings, synchros etc. And the clutch arrangement mentioned above.

It was lovely to drive, really nice... 915's will shift into 1st at 30 MPH without double-clutching if you really want to - although you'll not make a habit of it when you look at the price of the synchro's this wears..

One day, the 930 was bored and decided to eat 4 teeth off the 2nd gearset (which was both tall and kinda old); wasn't even trying at the time.

Being mindful of the transmission and it's weaknesses seriously interfered with the fun factor for me, until I went G50.


HTH.
__________________
'77 S with '78 930 power and a few other things.

Last edited by spuggy; 08-25-2018 at 11:45 AM..
Old 08-25-2018, 11:39 AM
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