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Old 02-27-2009, 12:06 PM   #21 (permalink)
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Exhaust systems are a voodoo science. What works for one car may not work well for another. What will work best depends on displacement of the engine, number of cylinders, and operating rpm. Small piping does impose a restriction to flow however it keeps the velocity of the exhaust gasses high which enhances the exhaust scavenging effect. Its a trade off.

Now if you have a turbo it pretty much deadens the exhaust pulses and you want a large diameter pipe to keep back pressure low.

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Old 02-27-2009, 12:32 PM   #22 (permalink)
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A stupid question: Why couldn't an exhaust system (at least the cooler downstream parts) be made of aluminum. Weight is the enemy, and all that...
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Old 02-28-2009, 09:35 AM   #23 (permalink)
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Originally Posted by davidgrey50 View Post
A stupid question: Why couldn't an exhaust system (at least the cooler downstream parts) be made of aluminum. Weight is the enemy, and all that...
Structural integrity of the pipe itself aside; cost. Exhaust is a component where the steel can be very thin because the shape of the product is structurally sound (section modulus relative to the direction of loading i.e. vertical vibration). Aluminum would have to be thicker because it is weaker and it is more difficult to bend although it can be done. Weight savings would be reduced by added thickness, plus aluminum costs quite a bit more per unit weight.

The C5 Corvette Z06 used titanium exhaust pipe which was even lighter than aluminum would be plus can handle the heat as well as steel. It was even more expensive. While weight is AN enemy, in almost all vehicle applications there is a cost/benefit tradeoff that is attached to weight reduction and "exotic" unseen parts typically cost high and benefit few.
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Old 03-01-2009, 02:19 AM   #24 (permalink)
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Aluminum tends to crack when subjected to vibration, steal flexes, exhaust also flows better when it's hot so aluminum would tend to cool it more, Titainum and stainless steal are insulators to a point, so they allow the exhaust to stay hot and flow better.

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