Headers Measured ID or OD?

[Nordy]

Hey guys

Sorry if this has been asked before, but did a search and couldnt find anything.
Just wanting to know if headers are measured by internal diameter or external diameter? Im assuming internal but can anyone confirm?
Wanting to measure my headers this weekend as they were already on the car when I bought it

Cheers
Jamie

[ratter]

I believe it is outside diameter, but happy to be proven wrong.

I believe pipe is always measured externally while hose is measured internally

[NOS540HQ2DOOR]

Thats right it is the od measurement

[Nordy]

Cheers guys appreciate that! Think I've got 1 3/4" 4-1's then so should suit to go cammed

[255-LS1]

I believe it is outside diameter, but happy to be proven wrong.

I believe pipe is always measured externally while hose is measured internally

not exactly. pipe usually carries a fluid and therefore is measured ID as this is what you are interested in for flow, capacity, friction etc. the pipes ID and wall thickness is dependant on the schedule of the pipe. Tube is usually structual therefore is measured OD. Wall thickness then comes into play. As far as i know fabricated extractors are made of tube, therefore it would be OD that is measured (as stated above).

cheers

[ADAM 26]

we deal with pipe all day every day.

depending on what pipe you are buying, they are measured id or od.

pipe we use is all id, pre-gal tube
exhaust pipe is od.
when building something with tight tollerence, then pipe thinkness and stuff comes into play