Rev limit and rod bolts on 3,2

[Thorsten S.]

Hello

I opened a thread in the 911 Forum and Kobaltblau recommended to link it here for more information. http://forums.pelicanparts.com/porsche-911-technical-forum/173405-rev-limit-rod-bolts-3-2-a.html#post1424643

Thanks

Thorsten

[KobaltBlau]

The question is, primarily, under what conditions have people seen 3.2 rod bolts fail? missed shifts, simply chipping rev limiter to higher rpm, etc. I thought a couple of people here might have seen these failures.

[Henry Schmidt]

Rod bolts are the issue. We have seen engines come in with rod nuts loose. ARP bolts in street cars will help.
The way they get loose is for the piston ass'y to reach a weight that stretches the bolt. What rpm is that? I don't know but heavier pistons will stretch the bolts at a lower rpm. Alusil pistons weigh more that Nikasil piston( cast vs forged).
We have found this smaller rod bolt (9mm), only used to make room for oil pump clearance, to be inferior and when we build racing engine we refuse to use this crank and rod combination. We build a custom crank that incorporates 3.0 rods w/10mm bolts and long stroke cranks. Since we began using this combination we have only had one failure. A broken rod that appears to have had a flaw from the factory.

[KobaltBlau]

Thank you, Henry. I thought you might have some input.

[Thorsten S.]

O.K. I have seen that there is room for improvement in the rod bolts. But when I look at the answers here, who had a rod bolt problem at his own car (only one person), the problem seems not so big or often.
Here in Germany most cars have 930/20 engines with 231 hp(Nikasil pistons and lighter) so perhaps this is the reason why I have never heard about this problem here.
And a person who bought a car here with 930/25 engine and 217 hp usually did not want to drive very fast or on track(almost cabrios or targas).

Grüße

Thorsten