Stepped Header Design
Stepped Header Design
(OP)
Alas, I found a topic that didn't have a single reference in this forum. I could hardly believe it. So how do you tune these cacophony of waves caused by a step header? I have Larry Muaex's pipe max software, but whats the real story? All lectures, references, and tirades welcome.





RE: Stepped Header Design
A proper engine simulation program is one way to do it. I've heard about but never used Pipemax. Even with engine simulation, it can be tricky to see what the effect of each pulse reflection is - the pressure waves get superimposed so that it's hard to see what's what.
Cut and try is the other option ... first in engine simulation software, then on the engine.
RE: Stepped Header Design
It got me thinking as to what the mathematical approach to doing something that complicated was. In my mind I know exactly what it looks like, but I have no idea how to solve it even holding rpm fixed.
It seems as if larry's method is to make the total length fo the step header approxiametely the same length as the tuned primary, but add steps so that there are reversion waves every so often which accent other rpm ranges. I have no idea how it arrives at the crossectional steps. Perhaps they are setup just to be sure there is a reflected wave? Then at some point velocity gets very low, so great changes in crossection are needed to create a meaningful pressure wave at the valve. At the same time I would imagine the overall effect of the header is less.
Really I'm just looking for some good literature on it. I have a car to apply it to, its a small displacement 4 cylinder, but I'm more interested in a general approach to any vehicle.
RE: Stepped Header Design
RE: Stepped Header Design
As far as performance goes, most of the "evidence" I have heard of usually shows only small gains over a properly tuned single diameter system of the same design (i.e. tri-Y, 4-into-1, etc.). I believe that many of the tests showing "improvement" can actually be traced to non-optimized merge collectors.
Andy Dunn of Popular Hot Rodding tested 7 sets of headers on one 408 cubic inch engine in 2004. The difference between all 7 was 0.5% in torque and hp over the whole 3000-7000 rpm band. A set of stepped headers was worth only 0.2% compared to a single ID set from the same manufacturer.
ISZ
RE: Stepped Header Design
RE: Stepped Header Design
Al
RE: Stepped Header Design
No they didn't. (Do they ever!?) But seeing only a 0.5% difference between 7 different sets of headers over the 3000-7000 rpm range has to make one wonder - though granted they were all picked to match the engine under test. In the end it is all pressure/frequency tuning and a header may hurt you in one spot but help in another.
I was also just thinking that real in-vehicle testing would probably lead to more differentiation as other factors such as gearing, etc. would tend to emphasize a certain portion of the RPM band.
ISZ
RE: Stepped Header Design
RE: Stepped Header Design
There are no problems, just challenges. Everett#2390
RE: Stepped Header Design
optimises steped headers from dyno figgers next step would be transiant response.
RE: Stepped Header Design
As the exhaust gas cools while moving away from the cylinder head it becomes more dense. A larger pipe cross section allows the "slug" of exhaust gas to keep moving freely and maintain the low pressure area behind it.
The over all length of the stepped primary will time the pulse wave return to cylinder accordingly.
RE: Stepped Header Design
...as I recall, the idea gas mass velocity was about 300 fps, is that still correct? Faster and pipe-wall scrubbing produces more friction/flow resistance; slower and inertial falls off.
RE: Stepped Header Design
RE: Stepped Header Design
Al
RE: Stepped Header Design
IMO, testing a set of these headers on a 408ci at the rpm range stated would be nothing but a waste of time and a exercise in futility. Did I read someone state something about constant reducing the diameter of the pipes? Well, that is going the wrong way friend. You start with a small (relatively so) diameter pipe and it is constantly increased to the intended size is reached. The real people to discuss this with is the header manufacturer.
Larry
RE: Stepped Header Design
ISZ
RE: Stepped Header Design
Larry