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We had my car on the dyno and couldn't get past 19.5 psi without the wastegate leaking. I have a BL 67mm 4" into a BL 4" down and midpipe going into a 4" to 3.5" adapter to a apexi spec gt. My tuner is suggesting the flow restriction with the 4 - 3.5 adapter is causing excessive pressure resulting in the wastegate not holding.

I agree, and was considering cutting the adapter out to make a smooth transition from the 4" midpipe to the apexi 3.75" pipe.
I am finding the apexi a little too loud under boost so I am considering a super drager. Does anyone know if the super drager will flow enough to allow 24 psi? I assume any 4" exhaust will be even louder than my apexi spec gt?

Any other exhaust suggestions?
 

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I'd don't buy your tuner's suggestion at all. Something is wrong with the wastegate if it's leaking like that. Plenty of people have made way more than 24psi on full 3" dp and exhaust without wastegate issues...I've hit 30 and my HKS 60mm GT wg does not leak. With the 67mm it's not like you have a huge turbo that really needs full 4".
 

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What kind of boost controller are you running? I have a HKS 60mm wg too. I wonder if my boost controller is not working properly.
I have an older/original Blitz SBC-iD
 

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my opinion is the opposite of your tuners, if you had a restrictive exhaust, and had the wg tied into your dp, you would more than likely experience the opposite of boost leaking. you would probably have something similar to boost creep which would give an increase in boost. i am running a 67mm with a 60mm HKS WG and a 3.5" exhaust and i do not have the problems that you are having. i think that the problem lies in the boost controller and/or the lines controlling it.
 

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Also has the system been pressured tested for leaks? The wastegate lines are near the manifold and DP so it's easy for them to crack over time... Crack in the line will prevent the boost controller from working properly.
 
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