I just bought an Invidia 70mm test pipe, but the opening is only 63.5mm (2.5in). When they say it's a 70mm pipe, are they measuring the opening or from the outside of the pipe? I've got a single 70mm T1R exhaust and I just want to make sure it matches up.

 

Nope, looks like you were sent the wrong one. The 70mm is an inner diameter measure.

 

yeah the inner diameter should be 2.75in did you get the one with the built in o2 fix? If so to save you the headache buy a O2 sim (extender) cause i've noticed that "built in" type doesn't work that long, my .02 cents
-Vito