How do you want the collector in a turbo manifold? Say for a 4-1 collector, do you want the choke CSA to be just bigger than the runner CSA, do you want it the same size as the housing on the turbo (if the housing hole is round), or somewhere in between? Or do you want it to merge down to a nice, small choke, then have a funnel to open back up to the size on the manifold or?

Like in this Go-Autoworks Top Mount, it looks like the collector choke is the same size as the opening in the mount flange.


(sorry about the big pic)

In a Hytech manifold, it looks like it just merges down to a large pipe width, passes through a quick turn, then into the turbo housing. I haven't found any good pictures of the flange shape though.



What about the square flange on lots of turbos? You take what would be a round-ish collector, open it up to a square flange, then the turbo housing rounds out a bit.

Wouldn't the sudden opening from the manifold-flange-turbo cause exhaust gases to suddenly expand/slow down/increase pressure? Or is that the point, with the flange acting as a slight anti-reversion step?



I realize most turbo/manifold designs are a combination of trade-offs, but what would be ideal.

I think I'll be using a Big 16G which convinently has a round hole where the manifold attaches to. Would you just have the collector choke match the size of the housing inlet, or have it choke down and then expand up to housing inlet size? Short or long expansion?