The only way what you're planning on doing will work (2 wastegate's) is if you had a twin scroll divided manifold which the OBX is not. When it comes to choosing manifolds to use one of the most important factors is how are the runners designed at the collector and 2) wastegate placement. Your current manifold has poor wastegate placement because the exhaust gases must go way up to reach the wastegate which is why you keep boost spiking and can't hear the open dump. To make the OBX manifold be somewhat efficient you have to go with your second idea which is placing the wastegate port at the bottom of the collector and ELIMINATING the original tube or else that manifold won't flow correctly at all.

 

i would cap off the original and just use the second one. also just some info u do not need a divided manifolds for 2 wastegates i have 2 on my set-up.

 

You're right, I should've explained my thought better because there are double wastegate single scroll manifolds that work very well. What I meant is the design of the OBX manifold isn't ideal for a dual wastegate setup, especially since the original runner sites so high. IMO if you just cap off the where the original wastegate sat and don't eliminate the pipe you cause the flow characteristics of the manifold to not be ideal because there will be an extra pipe just storing some of the gases instead of going towards the turbine and new wastegate port.

 

I don't think capping the original runner should matter that my difference. and if I still have problems I could just run both gates

 

I also have dual wastegates on my setup.. My stock wastegate is placed in front of the manifold to where only two of the four pipes were allowing air to exit through the wastegate... the other two (back two) were just bypassing it all together and going right into the turbo. Anyways, I put a 2nd wastegate into the middle of the manifold and it solved my problem.

 

Can you post a picture?

 

It has nothing to do with a downpipe. If the wastegate is too small or plumbed incorrectly it will cause this. Point of a wastegate is to regulate exhaust flow away from the turbine so the turbo doesn't spool anymore. Either replace the manifold or weld in another wastegate before the turbo.

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Dual Gates are on I will post pic tomorrow I have to run a vacuum line to the new lower gate so I haven't hit boost yet to see how it works. The shop did a awesome job on adding a extra runner to the manifold

 

Sorry the pic are not the best its in a really hard spot to get a pic of