pondering exhaust

[Bain]

I was reading some of the old threads relating to backpressure in the exhaust and how it related to the "scavagin" and I started thinking i have my mufflers close to the end of the headers and if i cut the rest of the pipe off it would create less backpressure but sacrifice the ability to suck the exhaust out but couldn't you hook something like a turbocharger to the end of the muffler to produce suction? also i was wandering is there some equation to determining how long of pipe you would need to produce just the right balance?

[Evil Result]

Ooooo..... your in a world of hurt, anyways.

Usualy after the exhaust headers you have the catalytic converter which is usualy required by state law and if you did cut everything off from your headers back well your car would burst into flames at some point.

A turbo isn't a suction device it actually uses exhaust pressure to spin the turbine, its actually creats backpressure.

[CarSuperfreak]

wow. first of all, try using some actual puncuation next time so we can understand you. And no you cant just attach the mufflers to the headers and call it good, it doesn't work that way. And why in the world would you put a turbo at the end of the muffler?

[Bain]

Originally Posted by CarSuperfreak

wow. first of all, try using some actual puncuation next time so we can understand you. And no you cant just attach the mufflers to the headers and call it good, it doesn't work that way. And why in the world would you put a turbo at the end of the muffler?

Sorry for the punctuation I didn't realize I was still in English class. I hope this better meets you expectations.

Also the mufflers aren't on the end of the headers they were close as in a foot and a half or so down from them. As far as the turbo, I was under the impression that a turbo sucked air in then comperessed it to shoot it back out the other end at a higher pressure hooking it to the end of the muffler was just something to aid in sucking the exhaust out so that less pipe is needed. I don't plan on doing it, it was just a thought that popped into my head.

[beef_bourito]

a turbocharger uses the exhaust pressure to spin a turbine which compresses air on the other side, and as we all know, more air means more fuel which means more bang. as for hooking it up, you put it before the muffler, as close to the exhaust manifold as possible, so the gasses are hotter therefor under more pressure, which means they spin the turbine faster. go to www.howstuffworks.com and look up turbocharger.

[curtis73]

Try not to think of it as backpressure being the function. All things (intake as well as exhaust) are functions of flow. Think of your exhaust as a soda straw. You blow air through it at a certain rate, then close your mouth; just like an exhaust valve opens, expells gas, then closes. During its exhaust stroke, the exhaust gasses reach a certain level of speed. As the RPMs increase, the volume of exhaust expelled increases. Since the diameter of the exhaust system is fixed, the exhaust gasses must go faster. There reaches a point where the exhaust can't go any faster since limitations like inertia, time, and friction overtake the properties of the gas. Equate this to breathing through a straw. Under normal circumstances you can sustain yourself this way, but take a jog and the straw no longer is adequate.

In an engine, scavenging takes place because the outflowing exhaust gasses reach a velocity where its inertia keeps sucking even after the piston stops pushing. Exhausts are tuned in this manner. Choosing a large exhaust means that the peak velocity is achieved at a higher RPM (hence why they are used on high hp/high RPM engines). Mismatching components will make any engine a dog.

There are thousands of websites with exhaust calculators. Just do a search for "exhaust size" or "exhaust calculator" and you'll find several. Visit Flowmaster exhaust's website for a chart showing HP/exhaust size charts.

Its not really that backpressure creates scavenging, its just that the more low end scavenging you create, the more backpressure there will be a high RPMs. The two terms were erroneously associated with each other.