When I order mufflers do I order to fit my OD or ID pipe?
Not always.ID for the front because the muffler slips over the exhaust pipe;od for the exit because the tail pipe will slip over the muffler.
Muffler shop!?The manufacturer dictates the muffler size based on what you want for flow. The muffler shop will install the pipe accordingly. I am putting 2.5 inch Dynomax Turbos on my car for better flow and less noise. The muffler shop will design a system to fit my muffler. Not the other way around. If the manufacturer says install this outlet towards the headers, the the muffler shop will shape their pipe to fit and same with the tail pipes.