DIY_EFI Digest V4 #586

[Greg Hermann]

>DIY_EFI Digest        Sunday, October 17 1999        Volume 04 : Number 586
>
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>In this issue:
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>	Re: DIY_EFI Digest V4 #584
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>Date: Sat, 16 Oct 1999 23:39:47 -0400
>From: "Gary Derian" <gderian at oh.verio.com>
>Subject: Re: DIY_EFI Digest V4 #584
>
>I haven't seen it but I've heard about it.  It seems to me to be similar to
>what Greg H described in having an expansion chamber to fool the exhaust
>into thinking it has reached the end of the pipe.  Also the megaphones cause
>pressure waves to be reflected back to the engine over a larger rpm range.
>4 stroke motorcycles have used megaphones.  The design is not quite like a 2
>stroke pipe, though.  I don't think a 2 stroke style will work on a 4
>stroke.

A megaphone is also a pretty effective (and efficient) device for
converting gas velocity back into static pressure.

Since the atatic pressure at the end of the megaphone is pretty much equal
to atmospheric, that means that the convergent (nozzle) point of the
collector, at the small end of the megaphone, will be at a static pressure
below atmospheric, and the engine will effectively be running against a
lower back-pressure than it does without the megaphone. As always--lower
backpressure equates to less pumping losses in the engine, and therefore
higher net output, particularly at high engine speeds/flows.

Greg