Formula Ford - Exhaust Design

[Hawke]

I'm sure this has been asked before, but I cant find any reference to it.

What is the best sizing of pipe diameter and primary length? I am getting a new one made, and would like to get it right.

[Brian]

Oooh, scary question! Art, who used to post here fairly often, did some research on the ideal header and it was pretty complicated. On the other hand, 1.5" primaries between 29" and 31" long into a 6" to 8" collector, with a 24" to 36" long secondary has worked for many years. Smaller diameter and longer primaries bias towards lower rpm peak, larger and shorter primaries bias towards higher rpm peak. Beyond that you get into tri-y collectors, 2 into 2 into one systems, stepped primaries, anti-reversion cones, and unequal length primary designs.

OTOH, if you aren't perfecting your tune to match your header on an engine dyno, it really doesn't matter all that much....

Brian

[stephen wilson]

To add to that, Primaries smaller than will be giving up H.P.

[Hawke]

Brian,

Thanks for that. I'm sure those sizes will work for a 56 year old driver of a 40 year old car. That extra 1 or 2 HP, isnt going to propel me to the front of the pack.