Would anyone expect to see gains by porting exhaust manifold up to 2 1/4 and running twin 2 1/4 pipes into a divided housing T4?

 

You might notice a little by keeping the two separate, you'd notice it more with a 4 cylinder motor.

I'd say it would be benificial but worth it? I don't know.

 

If you mean having 2 seperate pipes for the "downpipe", 1 for the exhaust, the other for the wastegate, you would have a little gain. It's common for Z owners to purchase "divorse pipes" or split downpipes. The theory behind this is that you won't have mixed exhaust gasses from the wastegate and exhaust flow causing turbulance as the exhaust leaves the car. The key though is that you would need to get a split flange to seperate the 2 as each one would have a seperate pipe that toward the bottom would exit out 1 exhaust pipe. Sorry for my ignorance here because I don't know how a turbo is mounted on a max.

 

no, i mean i have a divided housing turbo and i want to run two 2 1/4 pipes INTO the turbo, instead of one 2 1/2 pipe into the turbo.

I already have an open wastegate setup with inlet from manifold, outlet to atmosphere.

 

My fault, misunderstood.

 

Hehe! I like the way you think. I have been thinking about this too! I think there would be some gain in spool and a little bit in power depending on how much boost you are running and what size pipe on the downpipe. It's quite tricky to get it just right. two 2 1/4 inch pipes would help flow at the top end possibly but not necessarily help your spool which is the idea of split housing. Getting the right sizing is very important. I cannot remember what the sizes are for the flange on the exhaust housing itself but there is not much point going larger than that since it would just get restricted at the turbo anyway.

Also curious, how would you arrange the wastegate? Would you have two? I have an idea myself.

 

I am not sure if i would run two or blend the two pipes into one, done in such a manner so when the wastegate was closed there would be no crossflow between the pipes. Basically each half of the wastegate plunger would regulate one of the two pipes. I have seen it done before.

Nigel, were you going to run the pipes forward or still go backward with them. I think there is plenty of room between the moto and cross member, but i think you would have to drop the crossmember to get them out!

 

Well, I had a CAD drawing of my flange here at work, and the inlet area of one side of the turbine is about 2.5 inches. A 2" pipe has an area greater than that, so it would be useless to run 2 1/4... maybe...

I am pretty sure that the sum of all the exhaust port areas on one bank add up to greater than the oulet area of the manifold, thus the exhaust is being compressed through the manifold imediately after leaving the motor. Because this compression also happens as the exhaust from the 3 cylinders "blend" together, losses most likely occur in the manifold. If the entire manifold were ported and matched to a 2 1/4 outlet less losses would be had. However, the area of the 2 1/4 inch pipe would still need reduction to the flange. If a converging nozzle was used immediately before the flange (maintaining the required 21 degree slope of a venturi) the flow would actually speed up before entering the turbine.

Just a thought...

(I am practically having a conversation with myself in this thread...)

 

Well, I cannot really speak too much to this since I am an electrical engineer by profession and so fluid mechanics is not my forte. I imagine (and I could be wrong) that the 21 degree slope may be of some help it's hard to say ... If your pipe coming from the manifold is larger in diameter than the exhaust manifold, then you will experience some loss in speed and pressure coming out. You will speed it back up again when you enter the turbo. This may not be the most efficient way of doing things... also trying to get a 21 degree slope may not be so easy! I would save the headache and just come straight out of the exhaust manifold at whatever diameter that is (2"?) and when you reach the turbo, narrow it down or shape it there.