Boost is sluggish and down ?

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Boost is sluggish and down. This is a tdo6 18g conquest motor running e85 thur a cat and a muffler. Made 358 at 26 psi and is normally driven on a low 20's low 300 tune.

I made a 2-3 pull a couple of weeks ago and part way threw third i realized some thing was wrong. The logs showed the boost drooped off at the top of second and ramped back up sluggishly in third and was down 3 #'s.

Cat looks fine from the inlet side. Leak down reveled a bad exhaust valve so i replaced the head with a heavily ported one. Put it back together and the boost is off even more, wtf.

This is a surge prone set up, so i decided to tear the turbo down. But it looks fine to me.

Am i missing anything

I guess the next step is to run open down pipe and or tap my exhaust to log post turbine exhaust back pressure to try and rule out a problem in the muffler or cat i can't see.

 

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It was the cat. This time when i shook the exhaust There is a big chunk rattling around in the back half of the cat.

Any was the post turbo back pressure with a 3" 3 foot long open down pipe is .8 psi at 24 psi boost. vs 20 at 18 psi, with the bad cat and full exhaust. I wish i new what it was before the cat died.