OK... It was recomended by you guys to add an aftermarket exhaust to improve power on my Turbonetics car. I thought about it and came up with this rationale. Exhaust won't increase peak HP on a forced induction car.

My thoughts are this. Changing the exhaust to a free flowing exhaust WILL decrease back pressure allowing the TC to spool faster producing peak boost at a lower RPM. As the TC reaches it's peak predetermined boost the wastegate opens and dumps the exhaust.

The free flowing exhaust will not do anything to increase peak boost thus no increased peak HP.

The exhaust will help to lower peak EGT as it lowers backpressure.

I can't see gaining whp from adding exhaust. Correct me if I'm wrong. Let the debate begin.

Respect
JET

 

reducing the back pressure usually increases boost as well as everything else you stated.

 

Explain how it increases peak boost. Peak boost is regulated by the wastegate.

Respect
JET

 

by reducing back pressure

 

I never had to quote myself before.....

Reducing back pressure won't increase peak horespower in a TC car.

Respect
JET

 

i was wondering the same thing with my single turbo set up as well. i'm running a 3" exhaust with a stock muffler and i'm hitting full boost 8psi. at 2800 rpms. full boost at 9 psi. with high tq. numbers at around 4000 rpm. i can't see changing out my muffler for a so called free flowing muffler just to gain no more than 10 hp. maybe even less.

can any show a great increase from changing out the stock muffler?

 

You won't gain any peak HP... that's my point. You will be under peak boost longer becasue your turbo will spool faster. But peak HP will not change. Peak HP/boost is controlled by the wastegate.

Respect
JET

 

The boost setting alone doesnt determine how much power the motor makes, its how much air it can flow at a given PSI that will determine how much it puts out.

If you are flowing more air at the same psi you will get more hp.

 

That's the answer.... I didn't take that into account. Thanks for the help.

Respect
JET

 

more back pressure will put more pressure on the wastegate piston to open or bypass, no matter what the actual diaphram inside sees for boost psi. might not be alot, but it is still there.

 

Same reason cams and porting make more power. The engine is still a "pump" albeit with a turbine. Breath better in and better out=more power. That's why guys with stock exhaust on superchargers are making more boost then guys with the same pulley with full exhaust even though the one with aftermarket exhaust is making more power.

 

so with all of this said, is it worth getting an aftermarket muffler on an FI set up?

 

I don't agree with you. I have seen it many times that at the same PSI there was an increase in the peak HP with a less restrictive exhaust.
Also you said that it will not increase boost, I had an RX7 TT that had a downpipe and exhaust installed and it made more boost just from that upgrade. Why do you think it did that?

 

Yes.... More air volume out = more air volume in (@ same boost levels) = more power.

Respect
JET

 

So jet...do you now agree that your original rationale that directly correlated boost with hp was wrong?

 

See Post Above Yours.....

Respect
JET

 

It wasn't very clear....you could have just meant more power at lower rpms...I was just making sure as we know misinformation runs rampant on these forums...

 

I bet you race to exact cars with same turbo kit one with upgraded exhaust and one with stock exhaust will loose everytime...you know why you may not gain peak hp with 9 times out of ten you will but like you said you reach max boost faster witch means more hp at a lower rpm witch equals a faster car...why wouldn't you upgrade your exhaust with a turbo??? I'll bet you dyno your car with stock exhaust then right after and you'll gain 10 to 15whp....do it and see....and your boost will raise a bit...

 

He already said he knows that power throughout the powerband including peak power will go up with higher flowing exhaust.

 

My bad......sorry just read the first post he made and wanted to tell him how it is....