8psi is not far from standard, it wouldnt think it should lean out at that boost, mines running 10psi, and as far as i know its not lean (hasnt gone bang in past 8 years ive owned it, although mine has had a small pinking prob of late, i think its more down to type of fuel and timming slightly off, seems to have gotten better since putting in 97RON fuel.
people on here have been running 15psi ish on std fuel, only thing most have is the uprated fuel pressure reg and fuel pump.
im sure they will post soon if im wrong.
hope this helps some, if the RR you used was any good, they should have had some ideas as to the cause and cure.
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