CorneliusRox
Seasoned Rookie
- Joined
- Dec 13, 2012
- Messages
- 4,154
I think 30% is incredibly optimistic. You can say all you want about torsional loading and fastener material deformation, but i'm SURE ARP knows those things too....lets not forget ARP is a business that produces performance products. If the material could be torqued to 200 ft/lbs and never have an issue don't you think they would say that? Not a whole lot of companies are going to underrate their product, that's just bad marketing.
From an Engineering/QC perspective, i'd almost guarantee calculations and testing went into determining at what torque that particular fastener started to fail at a rate higher than ARP finds to be acceptable.
What this ultimately comes down to IMO, is people who are too cheap to go to either a 625 or a larger stud, have backwoods style convinced them self that pushing components to failure point is the norm. They've thought up these entirely speculative ideas and spread them as fact. IMHO, its your engine, do whatever you please, but don't tell the average guy that makes very mild power that he should be torquing to 150 ft/lbs.
30% is an arbitrary number. I was just throwing something out there. 30% is a pretty common target for safety critical components though.
As far as Engineering, I specifically referenced R99.99/C90 Weibull which is what every major engine and automotive company uses (or R99.99/C99 on very safety critical stuff). Do some reading on it if you'd like to educate yourself. It's a statistical analysis based on a torque to failure. It takes into consideration failure mode, torque mean, and spread. If parts are very consistent, you can safely specify a torque closer to failure, if there's a large spread, you need to drastically reduce the specified torque to limit failures.
I'm sure ARP would prefer to keep a good reputation rather than cut corners.
I think we're saying the same thing, but you likely have it in your head that a company makes 1,000 units and test to failure. It's more likely they do 8-16 from three separate batches, and do some statistical analysis. Then, just like stock head bolts, you're left with a specified torque that gets you to an extremely high likelihood you'll never see a failure.