Contour Enthusiasts Group Archives Forums Modifications Duratec Performance Single vs. Dual Exhaust

Why do the highest modified Supras and RX7's only have single exhaust? Does a quasi-dual exhaust give you anything except aesthetics since the gases have slowed by that point? Do duals really give you anything on a 2.5L motor that a good single exhaust system can't? I have duals on my car, but I have a hard time believing that a good single setup couldn't be as good. The only thing is aesthetics on the SVT's b/c there are two openings in the valence panel. Think about that... :rolleyes:

Why do the highest modified Supras and RX7's only have single exhaust? Does a quasi-dual exhaust give you anything except aesthetics since the gases have slowed by that point? Do duals really give you anything on a 2.5L motor that a good single exhaust system can't? I have duals on my car, but I have a hard time believing that a good single setup couldn't be as good. The only thing is aesthetics on the SVT's b/c there are two openings in the valence panel. Think about that... :rolleyes:

The main benefit of true duals on the Contour is because the exhaust pulses fight each other due to the design on the "Y" pipe.....but the reason a Supra has a single exhaust (other than its turbo) is it is an Inline engine......and the RX7 runs single exhaust for the same reason and other reasons as well...

Also, don't forget that your talking about turbo cars here. The turbo cut's quite a bit of noise from the exhaust so you can (and should) run a wideopen 3" system all the way back. Turbo cars hate backpressure, NA cars need a little back pressure (at least most do) to make power.

I have had three rx-7's (86 na, 87 turbo II, 83 street ported 4 port). NA rx's run true duals each rotor has its own complete exhaust path from the exhaust port all the way out the tip(not to say that single outlets are not available but at the time the true dual was the best bet for top end power when i bought mine from racingbeat. 2nd gen turbos ran a quasi dual much like the svt, mine had a 3" down pipe, 3" cat, split to 2.5 to run to the trust (greddy) mufflers. The third gen rx-7's are all turbo's and ran a single outlet from the factory.

Can't coment on the supra's.

Why do Ferarris, Corvettes have duals? Granted, Prancing Ponies and Vettes have larger displacement, but differnt motors require different parameters. Small displacement blown motors used in racing applications (and yes I know we are discussing street cars here) more often than not have duals. It's a contextual argument. Can a single be as good as a dual, yes I agree with you there. But it is application dependant. I am opening up my exhaust (Duals)to permit the escape of copious (broderline heinous) amounts of N20 laden exhaust gasses.

Also, I realize my response fails to acknowledge your accurat use of the term quasi......

Ramble off!
Mark

What if the ball don't come out? What you gonna do then?

Then you borrow your wifes favorite toy and poke that damn ball out of the pipe!

But seriously, the point was that gas flowing through a CONSTANT diameter pipe flows better than a changing diameter pipe.

Though i don't fully agree with the statement based on my fluid dynamics classes (yes i do have an engineering degree even though i'm not a practicing engineer). Every bend in the pipe will slow the gas down to some extent because gas is made up of particles and those particles will tend to want to go straight and hence "coagulate" at the bends. Now the amount that the gas slows down may not even be measureable with a single bend but it does slow down.

As a good example, take a dirty or painted 90 deg bend and stick a bead blaster nozzle in one end, pull the trigger for a second, and then look at the inside of the pipe (after letting go of the trigger :p ). The majority of the material will be removed from the outside radius of the bend.

But there are so many variables in exhaust design that i just decided to leave it to the guys that do it for a living and have the advantage of real world experience.

In short a properly designed single outlet should be able to net the same or more power increase as a good quasi dual. And no, the guy at the local muffler shop (in most cases) is not qualified to "design" an exhaust system.

ERRRR!!! It makes me nervous just reading the words "fluid dynamics classes". I'm taking that next semester, it's going to fun!

Just a little trivia here if anyone cares.

It is thought that the origin of dual exhaust, or at least the popularization of it goes back to when English motorcycles became popular. Triumph, BSA, and others with twin cylinders had dual exhaust and it looked really good.

Didn't the Taurus Duratec lose some power when the factory went to single exhaust at some point, then Ford went back to the 2 to 1 to 2 setup? Dunno about the pipe sizes and stuff, just something I think might be relevant here.