Contour Enthusiasts Group Archives Forums Modifications Duratec Performance Three inch exhaust = much more power

Ok,

I'm a EE and CS kinda guy, but I understand the basics.

Given the same engine, different diameter exhausts change the engine performance. A smaller diameter exhaust will increase exhaust velocity (up to a point)

So what does that do for you? It can increase exhaust scavanging. This is where the exhaust gas moving out (from other cylinders) helps to extract the gas from your cylinder that just fired, not to mention, if it leaves a slight underpressure (vacuum) in the cylinder when the intake valve opens, you can get a bit more fuel air on the intake stroke.

However, at some point, a small pipe stops being your friend and becomes a restriction to venting your exhaust gasses. So while you may make more power at the low end, you will probably lose peak HP at the higher RPMs.

Conversely, a large sewer pipe exhaust may look great on the dyno, driving it on the street may not net you the greatest "typically used" power. Sure, your peak HP goes up, but how many of you drive at 6000+ RPMs for great distances? I'd venture to say, not many.

Many here have reported that with gutted CATs and missing resonators the car seems more sluggish. I believe the Chris from CTA MotorSports has actually demonstrated this on the dyno.

The best quote I've read is an exhaust doesn't give you any horsepower, but can permit your engine to reach it's full potential.

Radical changes such as balanced true duals probably do make significant changes to the engines power output. However, this requires significant planning, design and engineering.

I'm not sure you are getting that from your sub $250 exhaust guy.

TB