Exhaust Back-Pressure
 

Very interesting.............

Mystic_River

Not true, in fact it is bad to have too large of an exhaust system.

" exhaust gas is hot. And we'd like to keep it hot throughout the exhaust system. Why? The answer is simple. Cold air is dense air, and dense air is heavy air. We don't want our engine to be pushing a heavy mass of exhaust gas out of the tailpipe. An extremely large exhaust pipe will cause a slow exhaust flow, which will in turn give the gas plenty of time to cool off en route. Overlarge piping will also allow our exhaust pulses to achieve a higher level of entropy, which will take all of our header tuning and throw it out the window, as pulses will not have the same tendency to line up as they would in a smaller pipe. Coating the entire exhaust system with an insulative material, such as header wrap or a ceramic thermal barrier coating reduces this effect somewhat, but unless you have lots of cash burning a hole in your pocket, is probably not worth the expense on a street driven car."

to read the whole article http://www.nsxprime.com/FAQ/Miscellaneous/exhausttheory.htm

I thought proportionate exhausts were better for naturally aspirated and bigger exhausts were better for forced induction...

for example 3" on an N/A 302 might be better than 4" on a 302 N/A

bigger is not always better contrary to what import guys think.

Those big exhaust cans do more damage than good like was said.

Take a look at most well built, high hp cars.....most race cars don't have 5" exhaust pipes with the biggest size headers available.

Back pressure is a good thing, just not too much or too little.

I don't know which mufflers you're talking about, but just because the import mufflers have large tailpipe openings doesn't mean the whole exhaust system is that size. Most of those guys run those mufflers with the stock 1 7/8" - 2 1/4" exhaust systems. As a matter of fact, most of the aftermarket import mufflers have 2 1/4" inlets and 2 1/4" - 2 1/2" out with a big ass tip stuck on there.
Bigger isn't always better, as a matter of fact most of the time bigger is worse. Just like everything else on your car, if you want optimal performance you will stick with something sized close to your desired HP/Airflow level.
If you run a 3" exhaust with 1 3/4" long tubes on a stock 302, add a 75mm throttle body and 90mm MAF sensor, chances are you'll probably lose a lot of low end torque and MIGHT gain 5-10HP at the top end. I would guess you'd lose anywhere from 20-35lb ft of torque down low, and thats not a worthwhile sacrifice.
SS

I didn't mean that the whole exhaust was HUGE, but those mufflers don't do anything for power, they make noise, that's it.....you don't get proper back pressure with those.

I happen to have a Vibrant Type V that I had on my Eagle Talon. it's just like you said it has the 2 3/8 inlet and 4" tip, but also has and adjustable outlet...I believe they call it a "tuneable" muffler you slide the piece in or out or completely remove it....it didn';t make my Talon any faster or more powerful...just louder, but then again we all know....noise means power :twak:

I don't understand what "proper back pressure" might be. Those mufflers are less restriction than the factory muffler, so they do increase power (however little it might be). They make noise because they are almost always a straight through design with no baffles. I actually had a 92 Talon TSI, and I installed an aftermarket muffler on it. It actually did make a difference in power, and the car would get into boost a little bit sooner. I know plenty of guys that had installed 2.25" Flowmasters on their stock 5.0s in place of the stock mufflers, and those all added sound and a little bit of power.
SS

As far as I know you want less back pressure on a turbo car because
the faster you can have the exhaust leave the car the faster the turbo will spool up. On a supercharged or n/a car the size of the exhaust will have
an effect on the power and torque curve Where a larger pipe can give
you a higher top end hp rating but you can lose some torque at the lower rpm range.

Thats sounds pretty close....your getting better with age.LOL

I must have been listening to some one that knew their sh#t,LOL.