Hey all,
I'm finishing up the welding on my downpipe and the last thing left is to plum the internal wastegate into the main downpipe. This is the design I have mocked up


The only issue I can see with it is that It might be hard for the exhaust gas from the wastegate to merge into the downpipe causing boost creep. As much as I wanna just weld this up and send it I'd rather do it once right. Do you guys think this would flow well enough to prevent boost creep on a gt28r at around 10-12 psi? If this design is not going to work I can do something like this, which from my very limited knowledge I believe would allow the wastegate to flow better, however, It would be a lot more work and questionable fitment so I would much prefer to do the first option if it won't be a problem at my power level.

Thanks for any help or advice

 

Consider a slip joint on the wastegate tube. The main downpipe and wastegate will see gasses at different temps, or more correctly, high temp gas at different times, giving differential expansion issues. Or so goes conventional wisdom.
DNM

 

Design number 2 would be much better. But honestly I think design one will also get the job done. Make sure you port your wg thoroughly and you should have no problem keeping boost down to 10-12psi. Once ported the Garrett internal gate works great.

 

Slip joint is definitely not a bad idea, I hadn't considered the heat differences thanks!

 

Yeah definitely going to port the wastegate, I may also do design one but more similar to the FM elbow style where I undivorce the two ports and create one big opening for exhaust gases to go through.

 

I picture the purpose of the separated waste gate tube oppositely. For me the primary value is when the gate is closed. That means I want best flow through the turbine for best spool. I put a baffle between my waste gate and the turbine exit to make it like the turbine exhaust is a smooth pipe that is an extension of the turbine outlet. This is not uncommon. Some weld it to the downpipe flange. I welded it to the turbine casting.



The separate pipe may well help waste gate flow also, for basically the same reason. So, it may indeed help prevent creep. Either way, it is a balancing act between the two flows.

Beauty of that is best flow though turbine when waste gate is closed, good / fast control when waste gate opens.

Well, I talked around that one, now didn't I?
DNM

 

Just a thought, but the wastegate hole looks to be pretty small, maybe only 19mm in some turbos.

That is going to limit wastegate flow to the point that you do not need a 50mm or 62mm wastegate dump pipe.
A smaller diameter pipe should work just as well, and it will be more flexible and less likely to crack at the welds, especially if its made longer and has a few bends.