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Dean:<br>
Absolutely correct. As outlined below, this is a well known
principle. When I was running, and building, engines for drag racing,
we definitely noticed h.p. differences both on the dyno, and on the
race course, after tuning headers. However, because of the size of the
exhaust collectors, (4" diameter) we could look in the collector and
clearly see the "lean burn" ring. Without going through the mechanics,
suffice to say we were able to "tune" the exhaust to add a few h.p.<br>
Bill Glaze<br>
<br>
Dean Pappas wrote:
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<div><span class="147295914-29112004"><font color="#0000ff"
face="Arial" size="2">Hello Dean ... Dean here.</font></span></div>
<div><span class="147295914-29112004"><font color="#0000ff"
face="Arial" size="2">Echo ... echo ... echo ...</font></span></div>
<div><span class="147295914-29112004"></span> </div>
<div><span class="147295914-29112004"><font color="#0000ff"
face="Arial" size="2">The short answer is that no tuning is necessary.
</font></span></div>
<div><span class="147295914-29112004"><font color="#0000ff"
face="Arial" size="2">4-cycle exhausts do indeed tune. This tuning is
not at all crirtical, and produces only a marginal horsepower
improvement.</font></span></div>
<div><span class="147295914-29112004"></span> </div>
<div><span class="147295914-29112004"><font color="#0000ff"
face="Arial" size="2">What happens is that as the exhaust wave front
makes its way down the long header it reaches the muffler can,</font></span></div>
<div><span class="147295914-29112004"><font color="#0000ff"
face="Arial" size="2">or the expanding cone part of the muffler. In
the case of a race car, it reaches the open atmosphere. In all of these
cases,</font></span></div>
<div><span class="147295914-29112004"><font color="#0000ff"
face="Arial" size="2">the gasses expand rapidly, causing a "reflected"
vacuum wave to travel back to the exhaust valve. If the length of the </font></span></div>
<div><span class="147295914-29112004"><font color="#0000ff"
face="Arial" size="2">header is correct, then the reflected wave will
return to the engine at the right time to help pull the exhaust out,</font></span></div>
<div><span class="147295914-29112004"><font color="#0000ff"
face="Arial" size="2">and fresh intake mixture into the combustion
chamber, behind it. This happens because of the valve-overlap. T</font></span><span
class="147295914-29112004"><font color="#0000ff" face="Arial" size="2">he
intake valve</font></span></div>
<div><span class="147295914-29112004"></span><span
class="147295914-29112004"><font color="#0000ff" face="Arial" size="2">is
already open </font></span><span class="147295914-29112004"><font
color="#0000ff" face="Arial" size="2">during the last 60 or 70 </font></span><span
class="147295914-29112004"><font color="#0000ff" face="Arial" size="2">degrees
of the exhaust valve opening</font></span><span
class="147295914-29112004"><font color="#0000ff" face="Arial" size="2">.
This is desireable, even with supercharged engines.</font></span></div>
<div><span class="147295914-29112004"></span> </div>
<div><span class="147295914-29112004"><font color="#0000ff"
face="Arial" size="2">As I said, this tuning is very non-critical. A
good figure for the length, from exhaust valve to place where gasses
may expand,</font></span></div>
<div><span class="147295914-29112004"><font color="#0000ff"
face="Arial" size="2">is anywhere from 12inches to 16 inches, for our
RPM range. Back when I ran my YS 120-ACs at under 7,500 RPM (16-13 N
prop)</font></span></div>
<div><span class="147295914-29112004"><font color="#0000ff"
face="Arial" size="2">I did run slightly longer headers.</font></span></div>
<div><span class="147295914-29112004"></span> </div>
<div><span class="147295914-29112004"><font color="#0000ff"
face="Arial" size="2">Regards,</font></span></div>
<div> </div>
<p><font face="Times New Roman">Dean Pappas</font> <br>
<font face="Times New Roman">Sr. Design Engineer</font> <br>
<font face="Times New Roman">Kodeos Communications</font> <br>
<font face="Times New Roman">111 Corporate Blvd.</font> <br>
<font face="Times New Roman">South Plainfield, N.J. 07080</font> <br>
<font face="Times New Roman">(908) 222-7817 phone</font> <br>
<font face="Times New Roman">(908) 222-2392 fax</font> <br>
<font face="Times New Roman"><a class="moz-txt-link-abbreviated" href="mailto:d.pappas@kodeos.com">d.pappas@kodeos.com</a></font> </p>
<blockquote style="margin-right: 0px;" dir="ltr">
<div class="OutlookMessageHeader" align="left" dir="ltr"><font
face="Tahoma" size="2">-----Original Message-----<br>
<b>From:</b> <a class="moz-txt-link-abbreviated" href="mailto:discussion-request@nsrca.org">discussion-request@nsrca.org</a>
[<a class="moz-txt-link-freetext" href="mailto:discussion-request@nsrca.org">mailto:discussion-request@nsrca.org</a>]<b>On Behalf Of </b>Dean &
Melissa Williams<br>
<b>Sent:</b> Thursday, November 25, 2004 12:20 AM<br>
<b>To:</b> <a class="moz-txt-link-abbreviated" href="mailto:discussion@nsrca.org">discussion@nsrca.org</a><br>
<b>Subject:</b> to tune the pipe <br>
<br>
</font></div>
<div><font face="Arial" size="2">
<div><font face="Arial" size="2">Hi</font></div>
<div><font face="Arial" size="2">Could you please tell me if I have
to tune the pipe length for a CD mkII system for the YS FZ91 , I
purchased this system several years ago and have just set it up.</font></div>
<div><font face="Arial" size="2">If I do have to tune the length
how do I do it and at what length ?</font></div>
<div><font face="Arial" size="2">I have the Cd mkII pipe +CD header
+ CDflexible header + CDmounting system.</font></div>
<div>I am running 20/20 fuel an a 14 x 10 apc prop with a Hyde
mount.</div>
<div>The YS idles at 1950 to 2000 and seems to max out at 8900 to
9000 rpm still seems rich (lots of oil out of the exhaust ) and the
high end needle seems insensitive until you go too lean and start
dropping rpm.</div>
<div>Any assistance is greatly appreciated.</div>
<div> </div>
<div><font face="Arial" size="2">Thanking you</font></div>
<div><font face="Arial" size="2"> Dean</font> </div>
</font></div>
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