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<DIV><SPAN class=147295914-29112004><FONT face=Arial color=#0000ff size=2>Hello
Dean ... Dean here.</FONT></SPAN></DIV>
<DIV><SPAN class=147295914-29112004><FONT face=Arial color=#0000ff size=2>Echo
... echo ... echo ...</FONT></SPAN></DIV>
<DIV><SPAN class=147295914-29112004><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=147295914-29112004><FONT face=Arial color=#0000ff size=2>The
short answer is that no tuning is necessary. </FONT></SPAN></DIV>
<DIV><SPAN class=147295914-29112004><FONT face=Arial color=#0000ff
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><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=147295914-29112004><FONT face=Arial color=#0000ff 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 face=Arial color=#0000ff 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 face=Arial color=#0000ff 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 face=Arial color=#0000ff 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 face=Arial color=#0000ff 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 face=Arial color=#0000ff size=2>he intake
valve</FONT></SPAN></DIV>
<DIV><SPAN class=147295914-29112004></SPAN><SPAN class=147295914-29112004><FONT
face=Arial color=#0000ff size=2>is already open </FONT></SPAN><SPAN
class=147295914-29112004><FONT face=Arial color=#0000ff size=2>during
the last 60 or 70 </FONT></SPAN><SPAN class=147295914-29112004><FONT
face=Arial color=#0000ff size=2>degrees of the exhaust valve
opening</FONT></SPAN><SPAN class=147295914-29112004><FONT face=Arial
color=#0000ff size=2>. This is desireable, even with supercharged
engines.</FONT></SPAN></DIV>
<DIV><SPAN class=147295914-29112004><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=147295914-29112004><FONT face=Arial color=#0000ff 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 face=Arial color=#0000ff 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 face=Arial color=#0000ff size=2>I did
run slightly longer headers.</FONT></SPAN></DIV>
<DIV><SPAN class=147295914-29112004><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=147295914-29112004><FONT face=Arial color=#0000ff
size=2>Regards,</FONT></SPAN></DIV>
<DIV><FONT face=Arial color=#0000ff size=2></FONT> </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">d.pappas@kodeos.com</FONT> </P>
<BLOCKQUOTE dir=ltr style="MARGIN-RIGHT: 0px">
<DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B> discussion-request@nsrca.org
[mailto:discussion-request@nsrca.org]<B>On Behalf Of </B>Dean & Melissa
Williams<BR><B>Sent:</B> Thursday, November 25, 2004 12:20 AM<BR><B>To:</B>
discussion@nsrca.org<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></BLOCKQUOTE></BODY></HTML>