manifold construction question
 

so i'm in the home stretch with acquiring parts and whatnot for my install, and one of the last things i need to do is get the manifold kit finished by a buddy of mine who's a pretty damn good welder.

My question is about the transition between the log and the turbo flange. I bought a JGS Stg II manifold kit some time ago, and since i am using a WRX turbo, i had them send me the kit with no flange, instead sourcing a turbo flange from a stock WRX uppipe. Now, it seems like most of the turbos people flange these manifolds for have rectangular turbine inlets, which works well with the rectangular radius plate they ship with the kit, as shown in the below picture:

JGS Stg II manifold kit

But on the WRX td04-13t, the turbine inlet is circular, as shown in the next pic (this is an updrade hybrid turbo, but it has a standard turbine side, from what i understand).

http://www.mjmturbos.com/images/WRXHYBRIDT04.jpg

My question is whether i should even bother worrying about using a round section of pipe to connect the flange to the log or if i'm overthinking it and i should just use the rectangular plate and let the exhaust find its way into the turbine inlet's round opening. My gut tells me i should try and match the turbine inlet's dimension as much as possible, but again, i could be worrying about a flow difference small enough to not matter too much (since i have other factors working against me anyway with the log manifold in the first place).

Thoughts?

I'd just use the rectangular radius plate, unless you can get a larger-than-turbine-inlet diameter pipe situated alright in its place.

For minimal gain, though, I wouldn't worry too much. To properly determine which is best, it'd take more effort than I think somebody replying to a forum post will exert.

i would use a round section isntead of the square tubing.

heh, that's kinda what i figured, atlanta. but it couldn't hurt to post. i think you're right, though, i'm probably just overthinking it.

loki, the issue is that if i use the supplied "radius plate" to connect the log t othe turbo flange, the rectangular port on the log will have a really crappy transition into the circular inlet on the turbine. i was curious if anyone had an opinion on how worth the time it would be to try and fab a circular transition in place of that rectangular "radius plate" between the log and the turbine inlet flange.

My feeling is that you'd want to have an extremely short "collector," hoping that the two transitions (mani/collector and collector/turbo) will act as essentially one, hoping to have less dynamic losses than two completely separate transitions.

Im building a log out of a stock manifold's header and a couple other bits. Total price = not a whole lot.