my 1990 civic ex sedan came with a new factory style exhaust-the piping size underneath looks like the hp racing cat back i had on my eg which was 2.5". looks bigger than factory.. hmmm

if i was to measure it with a ruler or tape measure-the number i get would be the od-outside diameter right? well what how do i figure out the indside diameter?

when a manufacturer says their system is let's say 2.5" - is that id or od?

 

anyone?

 

depends on the thickness of the piping they use. Usually when they advertise the size it's OD. So 60mm or 2.36" would be ID 2.25. Measure the ID

 

thanks, just what i was wondering.