Thread: Muffler Choices
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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
In principle turns add turbulence and a tight turns magnify this. A 180 deg turn adds turbulence as the gasses have different length paths to follow. This adds drag and back pressure. I belive a tight 90 can add .25 psi of back pressure in some cases.

Same thing for going up a size in pipe. If it is not a proper transition the gasses have to slow down to fast, turbulence is created and back pressure added. If you then add a reduction back down it again it adds even more turbulence and back pressure.

The better bend is a 'flattened' pipe of the same net cross section volume as the feeder and exit.

This can be evedenced when looking at most new intake manifolds where the intake runners look like flat tubes. The makes for a lesser variation in path distances around a bend which reduces turbulence potential and drag so better cylinder filling is had.

The need to make such a sharp turn might be a small part of the reason Porsche went to a chambered muffler but it was probably mostly for the durability and ability to control sound. If in fact a tight 180 has to be done, it might be a less restrictive to accomplish this with a chambered design.

With a chambered muffler it might be possible to creat an environment just inside the can that is a low pressure area. This way the high pressure coming from the turbine can escape quicker to a much lower pressure area.

On a system such as on a 930 where the muffler is right at the turbo this could be a significant plus and potental increase turbo response. The key being to have ways for the pressure to easily escape said can or environment. If this can be accomplished, it might be possible for the turbo to act like more like it is just attached to a short exhaust pipe to atmospher.

Still, we can brake the rules and still see a major improvement over stock and some times over what we think is a better design. Of course, a perfect exhaust for one build may not be perfect for another build and a perfict build has a cost.

We can get into trouble sometimes trying to think ourselves through a design. What we think might or might not work and what dose is not alwas the same. It is not untill it hits the dyno or the track that we know if we have been successful.

Just my two cents and not worth a penny more.
Old 05-13-2010, 08:00 PM
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