[88turboii]

you cannot mount an S4 turbo on a S5 manifold and nor vice versa.

the S5 manifold is completely divided (two equally sized holes, one for each rotor) and spools very fast. The S4 just has one big hole with a twinscroll flapper. Even with working twinscroll, the S4 does not spool as fast as the S5 manifold. however the S4 manifold ha slightly more potential for peak power

from the factory S5 manifold has a better wastegate design, but the wastegate door can hardly open before hitting the backplate. grinding material off the door and backplate or using a custom spacer fixes this problem. combined port area on the S5 is about 30mm. however the S4 wastegate (only 14mm from the factory) can be ported to flow better than S5