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Take it its detonating rather than pinking as they are two different things although often confused.
I can write you a good few pages on what causes det but thats not going to help you fix it so:
R5 GTT lump is a clockwork engine in that it is full mechnical for both fuel and spark (in real terms despite the leccy bits on it). You either have an air fuel mixture which is too lean under boost (be that because there is too much boost for the fueling available or the carb setup is incorrect) or you have an overly advanced spark.
Buy a reasonable timing light and set the ignition up as per the book and check the vac/boost advance/retard is functioning correctly. If that doesn't resolve it you need to look at fueling which means either a rolling road visit or on the road with a wideband HEGO sensor. For the GTT you want to be looking in the region of 10.5 - 11.5:1 AFR. Leaner to circa 12.5:1 will give you more power but idealy you want a bit of extra fuel sloshing about to help cool the charge and combustion chamber. IF you do not have access to a rolling road or a wideband HEGO sensor whack the mixture up until you see a sniff of black smoke (unburnt fuel) under boost. This will be far far too rich but will save your engine.
Running an engine permanently past the knock threshold under boost will result in a failed engine so don't do it!
Cheers
M
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