But its how the gases get from the exhaust valve to the turbine that also plays a big part. In the ays of E85 you tend to be able to mask a lot of things but I can tell you in the days of 98 if you wanted the most out of your RB20 or RB25 then a manifold helped. My 2c is whilst std manifolds make the power, you notic a big improvement in how the car drives and makes its power when driving it on the street or flogging its guts at the track.
My other 2c is if you can get a 6 into 2 into 1 manifold then it will work better again vs the 6boost like 6 into 1 manifolds