so im running a gt30R and at the track even at 6500 launch i was only getting about 11psi tops which i thought was kinda wierd. I made my own 3" downpipe to my old bushcur racing 3" catback with testpipe and bullet muffler. So just to experiment today i removed the rear section because im going to be making a straight pipe for the track well... i went for a test drive and tried the 6500 2 step i had set still from the track too see how it sounded and holy ****!! i hit 20-21 psi with it. Im currently running 24psi. I noticed inside the bullet muffler theres like levours or w/e that would be restricting all that but still wtf how can just a muffler reduce boost on a launch by 10psi thats pretty excessive if you ask me. I wasent expecting that big of a differnce at all. Just figured id post up about it because it was pretty insane sounding and gigantic gains.

PIC OF STRAIGHTPIPE AND VIDEO CLIP BELOW

 

Thats crazy. Have you thought of all other possibilities causing the increase in boost?

 

Its the scarifice we make to quiet things down. BR makes one of the highest flowing exhausts though.

 

I could be totally wrong...

But I thought boost was only related to things on the intake side of the motor. Shouldn't a more free flowing exhaust not effect, or in an extreme case(downpipe toooo big) not provide enough backpressure to allow proper turbo setup?

To reiterate, I could be totally wrong...

 

wow,20 psi huh???ive taken my muffler off before(to clean my can)and i couldnt help but to drive around.my car felt weaker with the muffler off.are u getting any more power besides the two step????

 

in all honesty it kicked the boost up in normal driving aswell and feels like i gained a bunch of hp on topend but i lost alot of anything i had preboost. The reason i was so shocked about this whole thing is the fact the buschur exhaust flows so well yet removing the muffler ends with this result. As far as the boost changing just to varify on 2nd gear w/o muffler i hit 28psi and let off quickly due to pump gas, put the muffler back on and hit the set 24psi. This really has me thinking so... at the track this sunday im going to make a few runs with muffler and get a richer tune and remove the muffler for another run or two to see if theres a big differnce.

 

Take off the exhaust, take the resistance off the turbine wheel...
It no longer has to push air out of a pipe or baffle.

Any muffler worthy of its name has some form of reversion chamber to bounce sound waves exiting the exhaust into a fiberglass, or SS dampening material. Now I don't have a degree, but this has to have some effect on the exhaust exiting it as well. Shortening the pipe will also have an effect on resistance as well. Same thing will happen with a cat. Take it off/on same thing. Its easier to push exhaust thru a hollow pipe rather than a honey comb.

I would tune for NO muffler, and adjust your boost according to your logs. (knock etc) Then go to the track and just do runs like that. You have runs with it on. Coming off the SB it won't feel empty on the bottom as it will never see it.

Then compare if you really want to analyze the difference.

 

I did the same thing, but i havent launched it with the straight pipe yet, but it sounds f-ing mean, i need to go to the track with it on. But funny thing is that my boost didnt raise, but it did gain alot of top end

 

track day is tomorrow.. here is the finished straight pipe, fits great, looks ok lol no tip but who cares its made for power right. Im going to run on racegas at 26psi and try both the straight pipe and muffler just for piece of mind
dont mind the **** coating on the bumper lol i tried to wipe it off but it made it worse

 

that looks badass! lol

 

can wait to see what kind of pwr u gain see u at gld

 

weird, i have an exhaust cutout that I open at the track and I didn't even get 20 psi on the stock turbo.

 

heres a video clip of it revving http://videos.streetfire.net/video/1...aa01130c67.htm

 

Just to chime in for your knowledge back pressure is NEVER good for any engine naturally aspirated or not, let me explain.

With a naturally aspirated proper exhaust sizing is beneficial becuase of the way exhaust moved through the pipes. Each pulse is accelerated through the pipe dragging exhaust fumes from the combustion chamber. Now obviously this benefit is variant depending upon the speed of the engine and the volume of flow. This effect is known as exhaust scavenging and will usually only be extremely beneficial through a set rpm range.

A Turbo engine does not see any benefit on exhaust sizing because the turbo itself its a major exhaust flow blockage. This means with a turbo you will always have some back pressure so the best course of action is to simply minimize that exhaust pressure with the largest best flowing exhaust possible. The biggest size usually ends up being a compromise of weight, noise, and how much money your going to spend on it. If it was legal a simple dump right into the atmosphere after the turbo would be the best exhaust.