to tune the pipe

[Dean Pappas]

Hi Bob,
Good to hear from you.
I used to use the long header to get more grunt from the throttle-up at the beginning of a vertical.
 

Dean Pappas 
Sr. Design Engineer 
Kodeos Communications 
111 Corporate Blvd. 
South Plainfield, N.J. 07080 
(908) 222-7817 phone 
(908) 222-2392 fax 
d.pappas at kodeos.com 

-----Original Message-----
From: discussion-request at nsrca.org [mailto:discussion-request at nsrca.org]On Behalf Of Bob Richards
Sent: Monday, November 29, 2004 12:29 PM
To: discussion at nsrca.org
Subject: RE: to tune the pipe 


Dean,
 
That is my observation. I had an AAC exhaust system on my OS1.20 years ago, and at most I saw an increase of about 150 rpm if I tuned the length. Hardly worth the trouble, IMHO. I had problems with that exhaust system, and ended up removing it and running the OS stubby muffler.
 
Bob.


Dean Pappas <d.pappas at kodeos.com> wrote:

Hello Dean ... Dean here.
Echo ... echo ... echo ...
 
The short answer is that no tuning is necessary. 
4-cycle exhausts do indeed tune. This tuning is not at all crirtical, and produces only a marginal horsepower improvement.
 
What happens is that as the exhaust wave front makes its way down the long header it reaches the muffler can,
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,
the gasses expand rapidly, causing a "reflected" vacuum wave to travel back to the exhaust valve. If the length of the 
header is correct, then the reflected wave will return to the engine at the right time to help pull the exhaust out,
and fresh intake mixture into the combustion chamber, behind it. This happens because of the valve-overlap. The intake valve
is already open during the last 60 or 70 degrees of the exhaust valve opening. This is desireable, even with supercharged engines.
 
As I said, this tuning is very non-critical. A good figure for the length, from exhaust valve to place where gasses may expand,
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)
I did run slightly longer headers.
 
Regards,
 

Dean Pappas 
Sr. Design Engineer 
Kodeos Communications 
111 Corporate Blvd. 
South Plainfield, N.J. 07080 
(908) 222-7817 phone 
(908) 222-2392 fax 
d.pappas at kodeos.com 

 

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