Thread: Exhaust Pipe Size

1999 Pontiac Grand Prix SE - 3.1L

I am wanting to buy a cheap universal muffler for my car as the factory muffler has just about rusted off. What size should the inlet side of the aftermarket muffler be which would allow the stock exhaust pipe to fit into the inlet side of the muffler? I plan to just clamp it on.

Also, I suppose it would be helpful to know what the inside and outside diameter of the stock pipe is before it enters the muffler. Thanks y'all.

Originally Posted by Fivefingerdeathpunch

On the single pipes all the way back it should be a 2.25in OD pipe. You can slide under there and just measure it yourself with a tape measure or a micrometer caliper.

Thank you. So, just to be clear I need to order a muffler with a 2.5" ID on the inlet side of the muffler, correct? 'Cause I need to have the stock pipe slide into the muffler some so I can securely get the clamp on there. OR, do I need to get a muffler with a 2.25" ID on the inlet side?

The reason I haven't measured it myself is because the muffler is still attached to the stock pipe, but only by a thread and I want to leave the muffler on the car until the one I order arrives.

Well... I bought the Thrush muffler #17713 which has a 2.25" offset inlet and a 2.25" center outlet. I cut out the stock muffler (what was left of it at least) and unfortunately the Thrush muffler was not flared so it didn't fit, it just butted up even with the factory pipe. I have a few scrap pieces of pipe so I'll have to rig it up, but wanted to let anyone else know that if you need to get a muffler make sure its OD is larger than the stock pipe's 2.25" or at least verify that the replacement muffler is flared.