I've read from various sources that when putting an aftermarket exhaust system on an Evo, the torque curve shifts into a higher range, and some owners have experienced a notable loss in torque below 3000rpm.

The thing is, i really like the progressive nature of the power and the good low-end torque (for a turbo) of the standard car (an E4). Is there something i can look for in an exhaust setup that still allows for an increase in power without reducing the torque below 3000rpm?

 

... and more boost means more torque. Ah, got it.
Probably will look at getting a full 3 inch (76mm) system. Cool.

 

I beleive an Exhaust is good for about 20-25 HP if you are doing a turbo back exhaust and you are looking at 10-15HP for a cat back system. Im going to be putting on a turbo back exhaust on mine along with a boost control wich will allow the spool to come up quicker in turn quicker acceleration and low end tourque. If you have any questions on anything check out my web site www.ajrperformance.com Still under construction.

Alexander
www.ajrperformance.com

 

Keep in mind that you almost never lose low end torque, you simply increase the torque in the upper range much moreso. The feeling of losing low end torque, if any is not correct when you measure on a dyno. It is simply because you have more power higher in the rev range is all. We run into that problem with WRX owners who feel like they increase lag when adding certain components. The lag is exactly the same or less but since we added so much more power on the top end it simply "feels" lagier.

 

Another reason to not worry too much is a lot of the exhaust is already at or near 3". I believe it might be 3" outer diameter, but its close. That and the twin-scroll turbo design will help eliminate a laggy car.

 

I saw some tests that were done on this.

The results were: Turbos hate backpressure.

In almost EVERY situation, a turbocharged car will make more power with a big exhaust than a small one.

At every point on the RPM curve, with both torque and HP.

All backpressure does on a turbo car is stop the turbine wheel from accelerating as fast as it should.

Turbo cars make it easy with exhaust sytems: BIGGER = BETTER.

Don't overthink the exhaust on a turbo car.

To prove my point, look at this dyno, and notice that with the bigger exhaust, the numbers are higher AT ALL POINTS. NO LOW END TORQUE LOSS.



THE DYNO HAS SPOKEN. EVO loves the large exhaust. As any DSM tuner can tell you.
The only question is: how much noise can you stand... larger also = louder.