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Bob:<br>
One small correction: the outgoing exhaust pulse, which is under
pressure, creates a small vacuum behind itself as it escapes; this
creates a low pressure area that helps draw the new charge into the
combustion chamber. I've used a "tuned" exhaust on engines as large as
540 cu. in. The tuning takes a little time on the race course, but it's
really worth it. It doesn't work quite the same with a blown
(supercharged) engine, because the blower pressure masks the small (by
comparison) vacuum behind the outgoing exhaust.<br>
Bill Glaze<br>
<br>
<br>
Bob Richards wrote:<br>
<blockquote
cite="mid20050523211209.85919.qmail@web30312.mail.mud.yahoo.com"
type="cite">
<pre wrap="">I had an AAP exhaust system about 13 years ago that
was tuneable to some extent. Playing with the length
of the system I was able to hit a sweet spot and gain
about 200 rpms, but was still a slight loss in rpm
over open exhaust. Of course, this was until the inner
lining of the header failed and exhaust started coming
through the outside braid.
The tuning dynamics are completely different from
two-strokes. On two-strokes, you are dealing with a
(forgive me if I mess up the terminology) reflected
wave that stuffs some of the excess unburned fuel/air
back into the exhaust port before it closes, but after
the bypass port closes, effectively supercharging the
engine. On a four stroke, you are using the inertia of
the previous exhaust pulse to help extract the next
exhaust pulse. Baffles and backpressure tend to defeat
this.
That is the limit of my knowledge on the subject,
perhaps someone else can elaborate (or correct me!).
Bob R.
--- <a class="moz-txt-link-abbreviated" href="mailto:patterndude@comcast.net">patterndude@comcast.net</a> wrote:
</pre>
<blockquote type="cite">
<pre wrap="">I've gotten a lot of recomendations to add a carbon
lightweight 4-stroke pipe to our lineup so I'm
starting to look at a 4 stroke pipe design. I have
some questions:
1. What are the proper pipe inlet diameters that you
desire on pipes
2. Worst reasonable case: how close is the pipe to
the exhaust port
3. What max temperature at the inlet do you suspect
(I'll be doing detailed research on this but want
your opinion).
4. Is it possible to tune a 4 stroke at all, or is
the muffling the only goal? If tuning is possible,
how does this work?
--Lance
--
District 6 AVP
<a class="moz-txt-link-abbreviated" href="http://www.aeroslave.com">www.aeroslave.com</a>
</pre>
</blockquote>
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