| Hi guys, I've been wondering about this and doing some research but didn't converge on a satisfactory explanation. So far I had thought that the high compression ratio of the NA motor (10.5:1) would cause detonation on high boost. This sounds reasonable but there are two facts that make me think otherwise:
1. A TT motor with 8.5:1 compression ratio is able to put up with over 25psi of boost without alcohol/water injection or retarding the timing. Why can't a 10.5:1 NA motor even support 15psi of boost?
2. Tuners are starting to modify the 335i, which comes with a 10.2 compression ratio, to have 12psi of boost on 93 octane and 13:1 AFR. BTW, it's pushing over 400WTQ with an ECU and upgraded exhaust. So is there any other reason why turbo'd NA motors blow up on over 9psi boost? Is it because of imperfect conversions (AFR not tuned, intercoolers not installed properly, insufficient cooling, etc.)? I think a turbo'd NA would be quite nice with good low-end torque and high-end power. Just some food for thought...
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