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Old Wed, Jun-20-2018, 12:04:07 AM   #25
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Default Re: A good example of why my engine internals have remained stock

Originally Posted by Volke View Post
In general for hardware, unless it's aerospace or safety critical, you don't design to or test to worst case conditions. You come up with a composite application profile that represents how your average customer will use your product and design/test to that. Also, the design metrics usually allow for a certain amount of failures before the target life. For example, when building a new engine, BMW may decide they want a B10 life of 100,000 miles and a B50 life of 150,000 miles. This means that they are okay with 10% of the population failing before 100,000 miles and 50% before 150,000 miles.

EDIT: On top of B10 lifes, they may also say they only want a 90% confidence interval when determining how many samples they need to test and for how long to verify that the design meets the requirements.
You hit the key in your edit...confidence interval. There is an inherent measure built in accepting that some will fail, otherwise like you said, you would have to model and test to worst.

I think finite element has become pretty popular in auto industry in mid 80s, so I'm not sure where the disconnect happened with some failures on these cars, but budgets and timelines always put pressure.

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'85 528e 164k miles (sold)
'05 M3 6MT coupe

All DIY: VANOS, WPC rod bearings, full SS (SS stepped V1 headers, catted S1, stock S2, SS sport), AFD E85 Proflex kit, Ohlins R&T/Hyperco 375f Swift 672r/GC street tops and camber plates, ST40 355 pfc08, 330 ZHP steering rack, diffsonline 4.1 diff with rem polish, E60 short shifter lever, AKG black diff bushings/subframe bushings, Rogue rtab, Sachs clutch/flywheel, rear main, Beyer driveshaft, valve adjustment, cooling refresh.

Happy to help with VANOS or any other DIY job around NorCal. Have various specialty tools (VANOS, RTAB, engine bar, valve adjustment, tranny jack, ball joint separator, pilot bearing puller, tap&die kit, etc).
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