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I understand the production model will have only one tailpipe while the original concept had two. Anyone know why they dropped one? My Tiburon has two and so did my Fiero (or was that four -- I don't remember). Anyway, I like the look of two rather than one. Opinions, anyone?
 

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im sure that reducing cost was the #1 factor. but, exhaust harmonics might have been a factor. this is a car that people are going to expect to sound very good at cruise and at WOT. or at least, heh, i expect it. i dont really know what the hell im talking about here, but how the soundwaves from the explosions in the cylinder and the pipe size are, i think, the main contributing factors as how the exhaust sounds. muffs and resonators change it, too, but they can only alter the sound so much.

ever hear an old integra with a fart-can and a stick driven by a guy who knows how to row the gears? i have, they sound great, almst like a race car. but, ive also heard the same car with a y-pipe and dual exhaust installed for a body kit. it sounded, well, not quite so good. most performance 4 cyl cars have only one exhaust, and i think that is done for a reason. correct me if im wrong! :D
 

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Most multi-tailpipe installations are purely for looks, if you want the real scoop, count the number of catalytic converters. GM is famous for differentiating between car models with the number of tailpipes.

That said, what really counts the most is how the exhaust leaves the chamber since it is the hottest there and occupys the most volume. By the time it gets to the muffler it has cooled to less than half the temperature (and consequently lower volume for a given pressure) it was when it crossed the valve so the further from the engine you get, the less tailpipe area you need.

Am already grossly simplifying (for a real explination see either H. R. Ricardo's classic "The High Speed Internal Combustion Engine"
or "Internal Combustion Engines" by either Lichty or Obert (two different books, same subject).

That said the easiest engine to tune is a six cyl with even firing. Given equal length pipes the exhaust pulses exactly occupy 720 degrees of crank rotation (personally think that is why a good six sounds sooo good).

By the same token, in order to get a smooth flow from a four (so the exhaust gas inertia from the last cyl helps start the next) requires a carefully tuned exhaust and sometimes an artificial restriction to lengthen the pulses. This is something you can also do with variable valve timing to some extent. You can also do a lot (and here the math gets complex) with pulse reflections. The idea being that one cyl exhaust leaves the cyl at high velocity, travels a certain distance, has a standing wave relected by a restriction (usually at a collector) bounces back up the pipe, is reflected again at the next cyl's exhaust and the second reflection helps accellerate the exhaust gas out of that cyl.

In general exhaust tuning like this is for a specific rev range - the longer the pipes, the lower the peak, but even with a low revving engine, by the time you get three feet from the valve, everything is done.

With a four, you never need duals. With a six and a really wild cam and high revs you can get into overlap so *sometimes* duals are warrented.

With an eight you have a mess since you cannot treat it as two fours unless you have a "flat crank" and then the vibration would kill you. The reason is that American eights do not fire L-R-L-R-L-R-L-R but rather L-R-R-L-R-L-L-R. This means that a true tuned exhaust would need to cross between banks (why the Ford Indy V-8 had a "snakes" exhaust system with the exhaust ports facing the center). Most people do not bother and just run headers and a pipe for each side.

I always found that a crossover pipe right behind the transmission (for room) was not only worth a few HP but remarkably quietened a healthy Pontiac V-8 particularly on the overrun.

Noise is a function of undamped exhaust pulses. The purpose of a muffler or a resonator is to provide multiple paths for the exhaust to smooth the pulses reaching the tailpipe. As long as you put the muffler on the other end of the car from the engine, you can do a lot of quieting without impacting the power.

In the late '60s GM did a lot of work with the Heimholtz effect with the result of the famous chambered exhaust system used in the Corvette side pipes and a very few Camaros that had no mufflers at all, rather precisely spaced bulges in the pipe that caused reflection (resonation) of the exhaust pulses resulting in a smooth flow at the pipe outlet.

Now some engines respond well to an expanding pipe following the reflection point (collector). The flat four VW and the Mazda rotary are examples of engines that did by using megaphones but with the understanding that prolonged exposure is a quick way to hearing damage. Two stroke engines (Mazda rotary is effectively a two stroke engine) also need all the help they can get in clearing the chamber so also use the expansion effect to make a short pipe act like a long one.

However my experience is that a properly designed and sized exhaust on a four stroke engine can produce just as much power in a street engine AND be reasonably quiet.
 

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2006solstice said:
Interesing read Padgett. I would imagine having just one pipe, and one muffler would also help save weight.
I seriously doubt that. Look at the pictures of the chassis. The pipes are not true dual. There is 1 muffler with 2 exiting pipes. I have no idea as to why they would use 1 exhaust tail instead of two. Sports cars were meant to have two pipes - that way they look balanced. Unless you want to give them 4...

It seems like a pretty dumb Idea to use only one exhaust. It can't save that much money - if any. Maybe they decided to go with 2 central exiting pipes instead of a split pipe design. That may be cheaper.

-Whit
 

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GM is going in for lotsa tailpipes these days but is all styling & has nothing to do with performance. It is what is going on at the engine that is most important in the power game, by the time you get to the tailpipe in a front engined car it is all over.

Pontiac has done it for years - remember the chrome splitters on 1st Gen Firebirds and GTOs ? Make as much sense as a 4" can on a riceburner.
 
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