Hi,

I have my GT2554r mocked up and I can chose either one of two styles of making the downwards turn:
Smaller diameter, but in my opinion a good flow:

A larger volume, but I think the gasses are more prone to swirl around:

The rest of the downpipe and exhaust will be 3" all the way, with a flex-part, a 200 cell cat and probably two Flowmaster FlowFX dampers. I have the feeling the first option will be better because it flows better, and going wider from there to 3" ( I will cut off the flange anyway, whichever it will be) will be a smooth transition. But what do the experienced gurus advise?

Cheers,

Hugo

 

Exit velocity isn't as important as the reduction in backpressure post turbine so I would choose the open option for that reason. Secondarily, the WG dumping into a larger, less restrictive cavity should be better for reducing boost creep.

 

There is power to be had with a divorced setup, even when the wg bypass is re-introduced in to the exhaust. HOWEVER, the WG introduction needs to be merged back in after both streams transition back to laminar flow. Elbows do this to radial flow, like the turbine outlet, but it still takes a bit of distance after the bend, way farther than the divordced housing you have listed. In addition, the 90 degree intersection between streams negatively affects dump tube pressure and interrupts turbine exhaust flow.

Go with the open. housing. It's probably cheaper and a proper divorced housing won't make any significant impact at 2554r power levels.