to tune the pipe

[Dean Pappas]

So Bill,
You would have loved watching this bit ...
Baby Brother was driving the then 12.0 second street-legal '69 Camaro down Interstate 80, with me driving alongside the rear tire, with my head out the window (think happy dod) listening for the "mellow sound" that indicated the RPM at which our left-to-right bank header crossover pipe was tuned. As you, no doubt, know, this pipe if placed correctly cancels the first anti-resonance of the headre, and improves the leave and short or 60-foot time. We got good at hand signals for, "now drive at 3000 RPM" and the like. We moved and re-welded that pipe twice to get it in the right spot.
 
Oh yeah, the burn spot trick! By my estimate, things worked best when you cut the pipe at 40% of a diameter longer than the burn spot.
 
Cool stuff, eh?
 

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 Bill Glaze
Sent: Monday, November 29, 2004 4:41 PM
To: discussion at nsrca.org
Subject: Re: to tune the pipe


Dean:
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.
Bill Glaze

Dean Pappas 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 

-----Original Message-----
From: discussion-request at nsrca.org [ mailto:discussion-request at nsrca.org]On Behalf Of Dean & Melissa Williams
Sent: Thursday, November 25, 2004 12:20 AM
To: discussion at nsrca.org
Subject: to tune the pipe 



Hi
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.
If I do have to tune the length how do I do it and at what length ?
I have the Cd mkII pipe +CD header + CDflexible header + CDmounting system.
I am running 20/20 fuel an a 14 x 10 apc prop with a Hyde mount.
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.
Any assistance is greatly appreciated.
 
Thanking you
                    Dean 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.f3a.us/pipermail/nsrca-discussion/attachments/20041129/7f169037/attachment-0001.html