Is this setup going to cause a exhaust flow issue?I am using forward swept headers both merged into a single 2.5 pipe and a 2.5 round t4 flange.

 

What engine? Power level? Boost? Is it a street toy or heads up race car?

 

It is a sbc 355 currently has a china gt45, changing to a vs racing 78/75. It has made 500/500 to the tire so far on 12 lbs of boost. I am wanting more power so probably will need more boost. It is more toy and race.

 

That divider wall is definitely a flow restriction. And your not gaining anything going to the 78/75. Those do have more modern turbines than the ancient turbos they're modeled after, but coupled with the small housing they choke early also. I picked up over 200hp by tweaking on the exhaust side of that turbo.
What size compressor is in that turbo?
What turbine housing?

 

Compressor 69 inducer,98 exducer, A/R .66 , 50 trim, turbine is 88 inducer, 77.5 exducer ,A/R 1.05

 

Yes it's a restriction, but does it matter? More pics of the headers, down pipe, and exhaust, a power goal number and more details on the engine configuration would help. It may be the restriction isn't enough for what you are doing, you can turn the boost up a pound or two and not really care that the restriction is there. Do you know what your drive pressure is?

 

The engine is a sbc 355,brodix ik 180 cc intake runner aluminum heads (flow 245 in. And 175 [email protected], cam is [email protected] on both,.489 lift on both ,114 ic ,114 lobe center I have a team g single plane with a csu carb. 12 lbs of boost on chassis dyno made 500 hp and 500 tq at 5000 rpm. At 12 lbs of boost back pressure is 20lbs. I am running pump 91 and spraying 30 gph of pure methanol afr 11.0 and 25 degrees of timing and plugs look safe timing wise. I would like to make 700 to tire. I also am running a th400 with a brake , ptc 3500 converter, 3:42 rear gear and 28 inch tires. Truck weighs 4000.The exhaust is all 4 inch.

 

I think 700hp @wheel on a gt45 is going to be a tall order, no matter how optimized the hot side is. Right now your pressure ratio really isn't bad, but that miss-match in the direction of flow is significant. That is just the wrong flange. If it was in the other direction it would matter less. Normally the turbo itself is going to be the big restriction in the system, and your hot side doesn't have to be perfect if you aren't max effort.

You could port what you have, use the exhaust soot as a guide, knife edge the scroll divider and you might pick up a little as you get closer to maxing the turbo. When you max out the GT45 (start monitoring IAT if you aren't already) and decide to go to whatever, make sure your flange matches the turbo foot. You might end up going to something like an s475, with the bigger 100/96mm T6, and it would give you a little room to grow. It might be modern enough tech that it spools similarly to the GT45 as well, I think with your 3500 stall convertor it ought to light up nicely.

 

I made this up today. Would this be a better option for my flange?