Ok I figured I'd ask I am running a turbo setup on my truck with a 4" down pipe and am thinking of doing a 4" cutout now how would that effect me? I do not have the talent to log any data would I need to make adjustments to the tune or what? That is all

 

Depends on how restrictive your exhaust is.
On mine with the stock catback it gets silly with just the small 38mm wastegate. I let out in third at 25psi.
With the cutout closed, i see 5psi no matter what.

 

Lets see 4'' dowmpipe and 4'' catback (MBRP kit) don't think its too restrictive so I'd see a 3 to 4psi gain? Which might be an average of 15hp per pound?

 

I think its goin to depend on your wastegate and turbo size..
There is but one way to find out!!!

 

i went to fender exit exhaust and it builds boost way quicker and picked up a 2-3#. less is better w/turbo. my turbo is small on the exhaust side, so it helped w/ backpressure.

 

mine picked up roughly 1 psi 17hp

3'' cutout
magnaflow exhaust

 

I have a 5" downpipe to a 5" cutout then necks down to 4" after that with a straight muffler. Cutout closed its 12-13psi, with it open its 18-20 psi.

 

I would love to go to a fender exit. But is there any way it could pass inspection?

 

So, you already have it tuned to 18-20 psi, correct?

What's ur WG doing then? Isn't it supposed to control boost to 12-13psi or what ever you set it to?

I am asking because my truck is tuned for 15psi through 3" DP and 3" straight through (when open) Varex remote controlled muffler. When the muffler is closed I can hardly build 4-5 psi but I did not push it too much because I don't drive hard with muffler closed as it's restrictive and very very quite as it's supposed to be when closed.

I am thinking to install 3" cutout before the muffler for track. Guess I will have to tune it for open cutout if my boost is going to increase to 18-20.

I noticed one time that my boost jumped to 20psi in third gear with current setup, muffler open and no cutout!!

I did not have time to test it again in 3rd gear because of transmission issues.

 

That's weird that all of you have noted increased pressure with the cutout open versus closed. On my setup I never saw a psi gain by opening or closing my exhaust valve,however it made much more power with the cutout open at the same boost level versus having it closed.