I am pretty sure the RB20 likes a manifold well before then. They really seem sensitive to back pressure and exhaust flow. The other RBs dont seem so sensitive to exhaust flow, but the little exhaust pulses of the RB20 seem to need some manifold help to spin the turbos. The full TD06-20G setups on RB20s always outpeform the bolt on setups. Even those that have had the exhaust housing gate mod or manifold gate mod