[Riceball777]

At what power level does the stock exhaust become a restriction? How much power witha vanguard exhaust system give me if I already have an intercooler castless downpipes and a jb4.

[Gmanuel]

Not enough to be worth it.

[musc]

Guys have pushed 600+ and beyond with stock exhaust so it's more about sound and weight reduction. Biggest restriction is downpipes which you are already addressing.

[csu87]

Less than a flux capacitor

[Riceball777]

Ok so there's no real performance gains with an aftermarket exhaust. It's all just for sound?

[Chris@BoostConcepts]

Most of this thread is circumstantial. Stock exhaust is fine up to a point, but ultimately as power level is increased the exhaust flow is increased. The best way to measure the efficiency of the exhuast system is in two parts. Firstly this applies primarily to turbocharged vehicles, as exhaust tubing for naturally aspirated vehicles can play an advantageous role in increasing intake charge air events.

So this is for turbo cars only...

There are two primary data points that should be recorded. Ti/P (Turbine Inlet Pressure) and To/P (Turbine Outlet Pressure). Anytime Turbine inlet pressure is increased as a result of turbine outlet pressure (poor flowing exhaust) horsepower is being lost. In a turbocharged car, turbine outlet pressure is bad ALWAYS! An exhaust builder should measure the turbine inlet and turbine outlet pressure of the stock system at max performance. If there is a significant turbine outlet pressure the new system design should account for increasing the exhaust flow. This can be done many ways as seen below:

Eliminating cross sectional area changes to maintain a higher exhaust gas velocity.

Reducing unnecessary bends that create pressure waves that cause velocity drops.

Eliminate flow obstructions such as poor flowing mufflers or inadequately sized catalytic converters.

Increase tube diameter to increase flow.

While the stock exhaust may flow well enough for minor bolt ons, as the power output increases the need for better exhaust flow does as well. The turbine wheel and housing handicap on the stock frame turbos masks poor flowing exhausts, while the exhaust may flow fine in the lower rpm range, as rpm increases a better flowing exhaust can help to extend the deficiency of the turbine wheel extending the power band.

A test that will show the truth of the exhaust systems effects is to remove it while on the Dyno and make a few runs with open Downpipes. If a significant change is observed. It is an indicator that the exhaust should be upgraded. A free flowing exhaust can assist larger turbos to spool better broadening their usable powerband even further.

I have not done any testing on this platform yet but will be testing the exhaust in the near future for performance increases with appropriate supporting mods on stock turbos. Upgraded turbos and eventually single turbos.

But as a blanket statement, I feel comfortable that an exhaust will not hurt performance and eventually will be needed if your goals include a higher power setup.

Chris

[Riceball777]

I completely understand that the best exhaust for a turbo car is no exhaust. I just want to know at what power level does the stock exhaust become a restriction to where a straight through 3" exhaust system will have huge substantial gains.

I want to keep the stock exhaust because i like how quite it is. If i'm at the 400whp level and an aftermarket exhaust will net me 10whp at the huge expense of it being louder than it is most definitely not worth it. but if the aftermarket exhaust nets 20+whp then its obvious the stock exhaust is a restriction then the aftermarket exhaust may be worth it for the extra power potential.

[musc]

Originally Posted by Riceball777

I completely understand that the best exhaust for a turbo car is no exhaust. I just want to know at what power level does the stock exhaust become a restriction to where a straight through 3" exhaust system will have huge substantial gains.

I want to keep the stock exhaust because i like how quite it is. If i'm at the 400whp level and an aftermarket exhaust will net me 10whp at the huge expense of it being louder than it is most definitely not worth it. but if the aftermarket exhaust nets 20+whp then its obvious the stock exhaust is a restriction then the aftermarket exhaust may be worth it for the extra power potential.

Catless DPs will give your stock exhaust a nice increase in sound without being overly loud.

[Chris@BoostConcepts]

Well if all you want is a peak number that 10whp is probably a out accurate at that level, maybe a touch more. I would be more interested in the area under the curve increase personally. Your only at peak power briefly. Your everywhere else the rest of the time!

[Riceball777]

Originally Posted by musc

Catless DPs will give your stock exhaust a nice increase in sound without being overly loud.

We all know that catless downpipes make very significant power gains even at the stock hp level and even more so at higher power levels. But were talking about power gains with a cat back exhaust system over a stock catback. particularly at the power level of a car that already has a tune, catless downpipes, intercooler, intake and most of all the other bolt on mods. How must power with a free flowing aftermarket exhaust help for power ?

[Riceball777]

Originally Posted by lcvette

Well if all you want is a peak number that 10whp is probably a out accurate at that level, maybe a touch more. I would be more interested in the area under the curve increase personally. Your only at peak power briefly. Your everywhere else the rest of the time!

If a downpipe back exhaust is only worth 10whp even its its through the whole rev range at the 400whp level then its not worth it and im perfectly happy with my stock exhaust system.

can anyone else confirm this to be true?

[Chris@BoostConcepts]

http://grassrootsmotorsports.com/art...ive-decisions/

If it yields that much on a stock car I'd have to say the gains would be more pronounced in a modded car... Oddly enough, the hks looks quite similar to the $400 manzo exhaust on eBay. Not sure of the muffler quality is the same but pipes are pipes.

[Riceball777]

Originally Posted by lcvette

http://grassrootsmotorsports.com/art...ive-decisions/

If it yields that much on a stock car I'd have to say the gains would be more pronounced in a modded car... Oddly enough, the hks looks quite similar to the $400 manzo exhaust on eBay. Not sure of the muffler quality is the same but pipes are pipes.

thanks for the link. After markets exhausts do almost noting for power according to that test on a stock car.

[jwebb335xi]

Originally Posted by musc

Guys have pushed 600+ and beyond with stock exhaust so it's more about sound and weight reduction. Biggest restriction is downpipes which you are already addressing.

I added downpipes last week and can absolutely tell that my turbos start pulling stronger more quickly. The car sounds just a bit more aggressive, but not with the windows up and radio on. I'm told that the remainder of the exhaust is about your personal satisfaction rather than making power!!

A DCI costs about $100 and sounds pretty cool too. Just saying...