Rebelrob

Got a simple question about exhaust pipes and headers measurement.

When one speaks of 2 , 2.5 or 3 inch exhaust etc.., is this size the OD (outside diameter) or ID (inside diameter) measurement?

I am measuring headers and the header collector is 3 inch OD, not ID.
The headers were advertised as 3 inch collectors.
Thanks,

Sigforty

The 2.5 inch exhaust pipe I pulled off my 71 was all OD.

sniperdiver37

Rule of thumb on header is bigger CI bigger headers. SB 2.5, BB 3". most give OD I believe. also unless your motor is super modified keep you exhaust pipes in the 2.25- 2.5 area or you will loose power with not enough back pressure.
Hope that helps

69427

Good grief. Will this old wive's tale never die?????

noonie

All tubing (exhaust, brake, plastic etc) is measuered by od, all pipe (under 12") is measured by id.

Rebelrob

OK. That is what I was looking for.
Thank you for the all the replies........

dstaley

Tubing => specified nominal value refers to outside diameter (O.D.)
Pipe => specified nominal value refers to inside diameter (I.D.)

EDIT: Crap, Noonie beat me to it!