Redvette_22

I've been told different things recently by both Vendors and end users, but cannot get an answer from manufacturers....yet. What I'm trying to confirm is this, how do you verify the header tube size? I have been told it's the O.D. of the tube and also told it's the I.D. of the tube. I have always been using the understanding that the measurement is the tube I.D.. What have others been told??

19Shark79

I am guessing it is on the ID of the tube. this is based on each manufacturer may use different thicknesses of material and coatings but in the end the ID should be the same right. Thats what makes the most sense to me.....but in the end its just .02

gerry72

Tube is always OD. Headers are made of tube.

Edit: Here's a link to clarify it beyond doubt: http://www.atc-mechanical.com/tube-p...size-overview/

Redvette_22

Pipe is usually measured by NOMINAL PIPE SIZE (NPS). Although it is related to the outside diameter, it is significantly different. For example, a 1-1/2″ pipe size actually has an outside diameter of 1.9″ NOT 1.5″.

gerry, according to your link, the O.D. is larger then the size advertised, as I copied and posted above. That would then mean the I.D. of a 1 3/4" header is in fact 1 3/4", not the O.D.

Redvette_22

This is what I've always been under the impression of, however, I went to buy 1 7/8" headers for my car recently, and the vendor tried to say the O.D. was how they are sized.

71 Vert LS1

I always thought pipe sizes are measured ID and tubing is always OD.

Redvette_22

That was always my understanding as well. So, if I want 1 7/8" headers for my 413, then the I.D. should be 1 7/8" and the O.D. somewhat larger...correct ?? That is what I expect anyway...am I right or wrong??

bashcraft

Wrong. Tubing, which is what headers are made from, is measured on the outside. The O.D. will be 1-7/8 and the I.D. will be smaller.

REELAV8R

The OD is the measured size for tubing. The ID will be determined by the gauge of the steel. Thicker steel smaller ID.

My 1 7/8" primaries measure 1 7/8" on the OD.

Redvette_22

What brand headers do you have ?

REELAV8R

Hooker. Side pipe headers.

TheSkunkWorks

Yep, tubing and pipe diameters are specified differently. My BB Hooker sidemount primaries are 2.125" OD, matching the sited dimension. FWIW, the engine sim software I use has entry fields for ODs, and a separate ones for gauges so it can most accurately perform exhaust flow calculations.