What happens when you reduce the boost? How does the torque curve change?
Reason I ask, for some reason I have the gut feeling that it's valve springs.
The intercooler cant be helping, but my gut seemed to go straight for that, so yeah... Scientifically unproven!
But regardless, if you reduce the boost, the point that the power drops should climb a bit higher - that is if it is a restriction. Meaning the curve should change meaningfully, and thus allow you to figure out the root cause - be it simply the IC, igntion or valves.
Does the boost sharply increase at the point that the torque dips, or does the wastegate/bov suddenly open a lot wider?
I ask this because that's an obvious pointer to an inlet restriction. If the air is piling up, the boost should rise, or there should be an obvious sign of boost modulation.
Does the AFR go a bit wonky? If I recall, a shaky AFR is a classic sign of valve spring issues.
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