Header theory

[Nova-Mann]

In the process of designing my own stainless steel headers that would allow slightly more than .050" clearance when driving over a cigarette butt, I realized I was wowfully short of technical theory and data when it came to what I call the 4-2-1 style header.

In a full length header system your pulses are separated by 270 deg., then 180 deg., then 90 deg., then 180 deg., 270, 180,------. In a 4-2-1 system the first stage is 450, 270, 450, 270,------. The second stage is wierd.

I guess what I can't picture is:

1) How the scavenge effect works in the 4-2-1 system.
2) How this affects tube size and length in the primary and secondary sections.
3) How a 4-2-1 compares to a set of shorty headers (not block huggers).

Anyone done any research on this or know of a thread that can shed light on this issue? Bad headers can negate a lot of things done right in the engine department.

[MoeBawlz]

are you looking to do a 4-2-1 or something like a tri-y... Over on cc.com we just had a little discussion on tri-y headers and theres some other tech on other headerstyles too.

[Matt@RFR]

If you're doing the research on exhaust theory because you want to, that's cool, but if you want an easier way out, all you have to do is buy a set of Burns collectors, and they'll design the headers for you with their software.

[chicane67]

Thats because the second stage is a combination of the two phases but it is also impacted by the negative pressure and scavenging effects of the other tube in the pair. By grouping primary exhaust tubes into a collector (or merge), the vacuum pulse from one cylinder can be used to create a vacuum on the other exhaust ports. This vacuum will cause the exhaust to begin flowing more quickly as the exhaust valve opens. The collector must be long enough and small enough to keep the inertia of the exhaust pulse optimized while keeping back-pressure low.

To visualize this, draw out the header that you have in question, and add the phasing elements first. Then read up on B's laws in physics..... and then study temperature and thermal effects on gasses.

But an eaisier approach would be to...

Go to the Burns site and read their technical papers on exhaust design and theory, it will save you some long winded responses. That is the most simple answer I can give you...... as an instrumentation engineer and having worked in the business of 'exhaust systems' I have studied exhaust systems (from fluid dynamic models and from an aero/thermal view point) and have implimented many different theories over the past 18 years....... but the list of things to add, to get a realistic end result, is long and very specific.

Scavenging effects are changed moreover by temperature and velocity. Now when you throw the vessal diameter and length into the equation, it too changes the effects..... and then when you add in phasing realationships..... the net effects can be quite different than once envisioned.

Goto the Burns site and start off with this.

Then read this which uncovers a little more on some mechanical issues that effect scavenging signal.

[Nova-Mann]

Good advice. I would much prefer that someone knowledgable design them. I love this site for all the info and experience that's available. Thanks for your input!