Intake and TB Compatibility??
The main reason being the opening is often less important than the plenium chamber inside the manifold. This is why on a correct setup a 78mm FAST will perform very well.
Although interestingly, TPIS do modifiy the LS6 intake to incorporate a 90mm opening and a 90mm TB and have seen good results, still not as good as a FAST 90/90 though.
You can always port the bbk manifold for the 90mm tb




