You need to turn down your duty. its way to high, if you have it higher, ur max boost will be lower, because the avc-r is controlling the overboost earlier and earlier. I have an AVCR also, you need to set it to like 52, then work your way up.
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My mates R34 30k kms, so turbo is new. dont need much duty if turbo is new, if turbo is older, then you need to add duty , to make up for wear ie. allow turbo to work a bit harder.
He had similar issue, but his wouldnt go above .072, and his max boost was set to 1.06 bar and duty to %86. so i took his duty down, to a flat line again, learned gear, then worked it back up from 50% duty. now it boosts to 1bar no problem . If your duty is too high, the AVCR will control the overboost. or possibility to overboost. You can turn this function off, or Turn the function down, so it doesnt control it as much, If you havea read of the manual it explains all this.
cheers.