Quote:
Originally Posted by radz28
It is also my understanding the timing is retarded at start-up to give it some rasp and aggressive sound. The timing comes back after a little bit of time, which might be what you're hearing.
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this is correct. while my zl1 (with borla exhaust) is loud on a cold start, my m4 (with awe exhaust) can literally wake the dead. and the m4 stays retarded, and therefore louder, for longer.
the reason the timing is retarded on cold start is to allow hotter exhaust gases out into the exhaust to warm up the cats, which work better at higher temps, to minimize emissions. there's no mechanical reason for the timing adjustment, and a lot of tunes actually take that out of the startup sequence.