how big is the protege's exhaust?
 

I've heard 2.25", but I find it hard to believe. Does anyone know?

I just measured the entry opening of the mazdaspeed muffler I got today, it's 2 and 1/16 inches.

Read "exhaust measurements". I went through from front to rear with a dial micrometer and measured.

that would make it 2 inch ID
scott

It's 2" ID from the second cat back to the flange where the rear section bolts up. The flange necks it down to 1 3/4" ID and that's what the rest of the muffler section is. I have no idea why Mazda did that. Mines 2.5" all the way from the cat back now.

Probably just to keep the noise down a little. I'd guess that they wanted to keep some of the performance without all the noise. They also have hp numbers that they shoot for, and that extra little bit of piping may have put them over their goal. Those would be my guesses anyway.

The Mazda pipes should be measured in metric for accurate numbers.. :)