Re: Choosing the Right Mufflers

[Tom Harais <tjhemh@domain.elided>]

Steve:

I wasn't saying the muffler did in that case. I was saying that the
combination of intake runner size and length, cam duration/overlap,
header size and length, was designed to provide reasonance in an RPM
range that actually scavanged the cylinders and increased volumetric
efficiency to more than 100% on a natuarlly aspirated vehicle. This was
an example we used in an engineering class I took.

I was saying, as you succintly put it, that it is all complicated: That
turbo mufflers were originally designed to create some resonance within
the exhaust like the above example, only not enough to actually
sacavenge the cylinder of course. The original turbo was designed for
the Corvair with turbo. Hence, their name. Their design isn't straight
through like a glass pack, but they have no packing, or "crimps" at
least not the original. They do have reverse flow as you pointed out.
But, some of the newer ones are even "tuned" with reverberating metal
plates at the ends of the internal pipes theoretically canceling out
sound waves as the exhaust flows out and around to the next pipe.

I think I posted earlier, glass packs are not necessarily "straight
through". They are packed and crimped.

And, someone else mentioned that "open exhaust" doesn't always provide
the most HP in a street application. Which I have experienced
personally. Ever see a Pinto that dropped it's muffler? The exhaust
manifold gets so hot it glows cherry red/white and begins to heat damage
all sorts of parts under the hood. (Post cylinder combustion going on
I'm sure, probably helped by a richening of the mixture due to loss of
backpressure combined with the O2 injected by the AIR system into the
exhaust manifold.)

Tom H.