Header design

Posted by starlet on June 15, 1998 at 15:44:52:

what headers would you suggest for a 4AGE? it's raced for drag use but the bore is stock- compression ratio of 11:1(ARIAS).
i currently use a 1 and5/8 diameter tube. 38 inches per tube- and 2.5 inches in diameter exhaust after collector with one muffler.
its length is 45 inches.4 to 1 design.

its design used to be ordinary- meaning to say the ones that have few and conservative bends.

with the same specs for the headers and exhaust, i changed the design. it's similar to TOSCO- one with dramatic bends. i seem
to notice stronger low ends but weaker high ends. what if i stick to the design but give the header a 1 and3/4 diameter tube?
what's the rule of thumb in creating a design for headers used for drag race?
what happens if i shorten or lengthen the header tube? exhaust tube? take off the muffler?
is there a page i could possibly read with regards to my questions?

Re: Header design

Posted by 82'Rolla on June 16, 1998 at 07:12:33:
In Reply to: HELLO??? IF YOU HAVEN'T READ MY POST DOWN THERE.... posted by body on June 15, 1998 at 15:44:52:

This is all I know....

29" primaries same ID as the exhaust port into a 5" collector with 2.25-2.5" piping from there. I haven't tried it, but to tell the difference an exhaust makes, you would really need a dyno to extract that last hp.


Re: Header design

Posted by T.O.O. on June 15, 1998 at 22:03:44:
In Reply to: HELLO??? IF YOU HAVEN'T READ MY POST DOWN THERE.... posted by body on June 15, 1998 at 15:44:52:

I'll try. First your primary tubes are too long for an engine that will be running in a fairly narrow rpm range, and high rpm at that. I can tell you this for sure, the higher your static and dynamic CR, the shorter the primary tubes should be. Assuming that you're talking inside diameters, I think that before you really start cutting, consider stepping to 1.75" as soon as the tubes are all parallel. If you make the 1.75" sections fairly short, you can make (4) 1.75" tubes with ends expanded so you can slip joint them to your main headers, and you'll also be able to change the slip fit tube lengths to "find" what the engine wants. Your collector doesn't sound bad as far as the diameter, however, one thing that really can make a difference is fabricating a "goilet" in the collector...that's a 30 year old name that means extending the tubes merge in the collector, so it'll look like a diamond shaped spike in the center of the 4 tubes. I suggest trial and error with a good accelerometer.
Next set of headers: Make sure that the primary tubes have a deliberate mismatch with the "port shaped" flange exit. Try to achieve a pretty good amount of step at the top and bottom of the intersect, and also some on the sides if possible. You want to make this so that the flow out can exit the port/flange into the larger header, so the step will impede reverse flow, which is absolutely a necessity on a normally aspirated engine...and it doesn't hurt on boosted engines either.
In looking at your lengths again, does your collector neck down to the 2" Honda donut size, it shouldn't. You can machine an aluminum donut or use some of the braided stainless flex tubing on the market to allow engine movement, try 2.5" all the way. The muffler is another trial and error thing, regardless of how it flows. Hope this gives you some ideas.
.........................................T.O.O. .................................