Header Design Choices

[SoCar72]

A forum search didn't yield the answer(s) I was looking for, so I'm opening this can...

Various vendors, manufacturers, and eBay auctions offer a variety of header designs (lengths are guesstimates from photos) :

-6 (about 12" primaries) to 2 (about 6" secondaries) to 1 collector - full run about 18" (eBay).
-6 (about 18") to 3 (about 6") to 1 collector - full run about 24" (saw a photo a few years back).
-6 (about 20") to 2 short collectors - full run about 24" (Clifford offering).
-6 (about 20") to 2 long collectors (about 16") - full run about 36" (CI offering).
-6 (about 36") to 2 collectors (about 9") - full run about 45" (Hooker Super Comp, I believe).

All appear to be 1 1/2" primaries with 2" or 2 1/4" collectors

Does anyone have any input on the performance differences among these designs? The greatest design differences being the long tubes vs. short tubes, the single collector vs. dual collectors, and long collectors vs. short collectors.

I'm considering options for my Falcon with focus on good street performance. There will be other engine mod's in the future, so I'm not looking at this in relation to a bone stock motor.

 

[StrangeRanger]

The longer the primaries, the lower the RPM for which they are optimized.

 

[wallaka]

And, the longer the collectors the better. Generally speaking.

 

[aussie7mains]

In all seriousness, if your running on the street it barely matters, when designed cast iron manifolds will do quite well. IMO id simply make sure you get the centre port split into two then run whatever header you like with the lowest restrict system you can fit.
Lotsa high performance inline sixes get up to 1 BHP per ci with only cast iron headers twin outlet, your not likely to get to that with the LOG head.
The theoretic optimum pipe diameter is around your exhaust valve size, so about 38mm ID or 42mm OD
longer is better, the joints into the collectors should be nice and smooth with the outlet OVER the collector, not inside it, your 3.3litre six will need about a 58mm outlet and complete exhaust system. In my experience twins system to the back sound a bit V8ish, but single seems to work as well.
A7M

 

[SoCar72]

All - That helps a lot. Thank you.

Lower RPM is key, so sounds like the latter 2 are my prime choices.

 

[wsa111]

The Hooker has 1 1/2" primaries, 38" long into 2 1/2" collectors.
No comparision dyno test has been run, but my combination with the hookers put out 145HP on a chassis dyno test.
I believe all the other headers are a 1 5/8" primary pipe but with way shorther lenghts. Bill

 

[SoCar72]

Chassis dyno - those numbers are at the rear wheels, right? Nice!

Do you know if those headers will clear the firewall in the round body Falcons ('63)? The application listings state "all 144,170,200 Mustangs", and Falcons share very similar chassis designs. It seems they would clear, but I haven't found a definitive yes nor no.