Could any of you please tell me what size the primary tubes are on a typical run of the mill street header (1985 GSL 12A)? I searched and couldn't find it. Thanks!

 

your "run of the mill" header is actually a plain ol' manifold that doesn't have runners/ tubes. it's a log.

if you are referring to a performance header, i believe the average size is 2".

 

Thanks! I was asking about a "run of the mill" performance header, not the factory manifold. The log is being replaced on saturday by an old but never installed header and I just needed an estimated primary size for a couple reasons.

 

If by primaries you mean each tube before they collect, I think I read somewhere that racers use 100" primaries for optimum power, but If you search there are a few good threads to read such as an awesome one on pressure wave tuning, and probably some that will pop up if you search header primary tooo.

 

Oh yah. I think with the 100" primaries the tubing itself was 2" OD with an 1/8" thickness, So 1 3/4" ID, which is what racingbeat uses in their headers. And if you didnt care about length of the primaries, sorry to have complicated things.