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

we all need the TURBOLATOR(R)

It was a serious question.

I was taught that by opening up your exhaust and decreasing back pressure, you are increasing valve overlap. And if you are increasing valve overlap, you are also increasing the amount of intake charge that is lost to the exhaust system.

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

There is also the sound wave component that helps or hurts exhaust performance.

The only way to really know is before and after dyno plots. The butt dyno is notoriously inaccurate. I believe the "thinner wallet coefficient" does throw off the calibration of most butt dynos

TB

Does anyone on this site have true dual exhaust? Wouldn't that require two cats? How would you factor in the oxygen sensors? I'm considering getting glasspacks aswell. Has anyone had these installed? What are the pros and cons?

Try the search feature for true duals searchy searchy

Yes, some have it. I believe some have used a single cat with two in and two out, so the cat also functions as the X pipe.

However, do a search for all the details.

Regarding the CATs, the four O2 sensors used on the 96 and newer Duratec engines only check the pre-cats in the manifolds. The two sensors upstream of the CATs check the mixture, the two downstream check pre-cat efficiency. So true duals will not impact that. However, if you gut the pre-cats, you need to either make MIL eliminators or extend your O2 sensor wiring to the main cat and fit the two sensors that check the pre-cat efficiency aft the main cat or cats.

HTH

TB

is it just me, or does European sound like he's using car-talk magnetic poetry to compose his posts?

Ok, I'll bite. What is "car-talk magnetic poetry"??????

I had the glasspack installed, however the straight pipe growl sound I got was reduced 60%. I'm going to have it removed. I still want a glasspack though over a resonator. The one I got was close to two feet in length with a 3 inch core. Will a smaller glasspack in terms of the length get me a louder sound without any rasp?

Thanks,

EuropeanConnection