| :they retain more heat energy in the exhaust to spool the turbo and are less likely to crack over time from heat cycling like tubular turbo's do. actually, cast manis have more thermal mass, and will result in slower spool than a tubular manifold of the same geometry. The reason for this is the heavy iron manifold absorbs heat energy from the exhaust flow that could otherwise be used to spool the turbo. The tubular manifolds heat up much more quickly, which results in more heat energy to spin the turbine The upside for the tubular is that the semi even length runners will deliver the exhaust pulses better and be less likely to send pressure waves back into the cylinder.
:the biggest benefit for the tubular manis is the ability to use external wastegates and different exhaust housings. Aliaz knows way more about all this than me, but he said that the 3071's with internal wastegates had clipped the inducers to fit the WG housing which hurt's efficiency. When you move to a t3 3071 you get the turbine with better efficiency.
:but if that's the case, then therin lies the problem for you. If your gt675's have a clipped turbine wheel because they are designed for a internal WG housing, then you would need to replace the turbine with the housing. The GT2860 does not have clipped turbine wheels. The reason the 3071 has a clipped wheel is to fit a T3 wheel into a T25 housing. The 2860 was designed to fit into a T25 housing, so no clipping is needed.
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