Thanks for reading. I am going to get to the point right away.

Let’s assume you have a Honda motor with some good cams making good power with a custom header with true merge collector, stainless steel.. let’s assume that setup is making 250whp with full 3 inch exhaust fully tuned.

Now, take that same car and replace the header with a cheap *** header with smaller diameter runners, no collector… etc… your basic made in Taiwan cheap *** header… Assuming you dyno it open header, with the same gas, tune, dyno, it is possible that it can make the same power with the same curves?

Let me rephrase…. What would it mean if it made the same power, the same way?

 

it isnt very likely that it will produce the exact same curve, especially if one is ran with an exhaust and one without. maybe dave, randy, or danny can chime in with some more insight about the length and diameter of the primaries, and boxed collectors vs. merge.
OT: did you actually have this happen???

some reading i copied out of a book i have laying here, "desktop dynos" by Larry Atherton. some or most of which you may already know, but it does a decent job of generalizing exhaust theory in a short amount of time.

"two of the most important are header tubing size and length. tubing size is really a measure of system volume and, on open headers at least, determines the restriction of internal passages. Large, free flowing tubes produce lower pressures. lower positive wave pressure generates lower amplitude suction waves, reducing scavenging and cylinder filling. on the other hand, smaller diameter tubing creates higher pressure that, while generating strong scavenging waves, increases restriction and pumping work. as is the case with every component category in the internal combustion engine, the best power is produced by finding a balance between two or more counterbalancing factors. here an optimum balance lies between the excellent scavenging affects of small tube headers vs the reduction in restriction and pumping work produced by large tubes. the balance tilts one way or the other depending on cam timing, engine displacement, rpm, and several other factors.
tubing length affects when the negative suction wave arrives at the cylinder. longer tubes delay the scavenging wave, appropriate for low-speed applications when more time elapses between the opening of the exhaust valve and the overlap period. shorter tubes return a scavenging wave more quickly and "tune" at higher RPM."


Modified by lohatch at 8:09 AM 9/29/2005

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Nikos &raquo;</TD></TR><TR><TD CLASS="quote">Let me rephrase…. What would it mean if it made the same power, the same way?
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I would guess that the bigger header wasn't necessarily better for that application...

OR

That *good* header had more potential for higher compression, longer stroke, bigger bore, more tuning, etc...

 

Nikos what it would means is that the header design was deifntley not optimal for that engine and had muhc tuning to be done. Then length could have been off by a few inches it could have the wrong calculated collector size etc.

A while back we built a very adjustable setup of drasticaly different design from that the major race teams was running, they dynoed very very simliar back to back, but our piece has plenty of tuning left on the header and on the engine. With fine tuning it should go far beyond the old piece.

Long sotry short that custom header was wrong for the setup IMHO, but there could also be some tuning issues we have seen it before tuning issues as in spark and fuel.

oh and small runners are not a bad thing

 

thank you, that makes sense in a way