Header/Exhaust Designs
First of of here are some specs of various headers and exhuasts:

Spoon - Header 45 -> 48.5 -> 60.5
Exhaust 60.5 Tip:65

Mugen - Header 45 -> 50.8 -> 60.5
Exhaust 60.5 -> 45 Tip:89.1

Amuse - Header 45 -> 54 -> 60
Exhaust(dual) 60 Tip:100

Stock - Header 45 -> 54 -> 60
Exhaust 60.5 -> 48.6 Tip:Unknown

Here are some things I found interesting.

The stock header seems to provide more high end than Mugen because of the un-equal length runners and fatter piping. Spoon seems to favour high end as well, but the piping is even smaller. Amuse header is basically a Mugen copy with fatter mid-section, and on dyno it provides similar gains as Mugen, but a bit more than stock in the high-end. Anyone has any idea makes both (Amuse & Spoon) header of such different designs both help in the top end?

Spoon exhaust seems to have shown some peak gains while Amuse ones seem to have proven to show around 3-5hp at peak. Mugen, on the other hand, shows almost none. Here's the thing though. I do not understand how Mugen went with such tiny piping. I can't imagine the F20C needing that much backpressure, and not cause any negative effects either. I wonder why they didn't do with fatter piping to create at least a tiny bit of gains. It puzzles me why they didn't even keep the stock piping size and went to a smaller size for their own.



Any input is welcomed.

 

The stock header is manufactured with heavier wall tubing and mass production techniques so it has slip joints. The tubing ID is not comparable to the others that have joints butt welded.

 

I thought the numbers were measured inside the tubing. Maybe I was wrong.

 

The piping of the stock header seem to be quite thick however that header is mde out of double layer so the I.D. is actually smaller than any aftermarket headers which listed same as stock.