So I'm starting to think about a custom exhaust system. Problem is, I HATE 99% of the mufflers out there and I LOVE the look of the stock GT muffler. Mine is in mint condition as well but my flex pipe is about ready to need replacing. I figured while I was at it, I would replace the entire thing with a high flow exhaust manifold and 2" stainless piping. I'm curious if I were to keep the stock muffler, if it was going to be counter productive to the decrease in back-pressure even though it's at the end-of-the-line.

This isn't really a post to try to find an alternate muffler so much as it is to become more informed of what would happen if the stock muffler was kept.

The stock muffler isn't terribly restrictive. Piping going into it is 1 7/8" so you would have to cut a hole larger in the end of it and weld in the 2". Outlet is 2" though, so you'd have a true 2" exhaust. Piping on our cars gets smaller. Near the end where it bends over the rear control arms. I think I measured 1 3/4" when I took mine off, which is stupid. Most of the pipe before it is 1 7/8" or 2". Unfortunately because yours is OBD2, you can't delete the cat, which enhances the sound (and the 5S-FE has a really great sound. My Honda buddies hate me for it) but opening it up a bit will encrease flow and you should notice better throttle response and more MPG. You'll keep torque, because of the smaller size and won't really increase hp much, if at all... But it will sound deeper and feel a bit quicker on the response.

I ran a full 2" SS exhaust on my 99 Camry LE with a 5S motor, so what I'm saying is what I have found.

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I realize that I will have to still have a cat and I'm not looking for any extra sound or really any performance for that matter. I just figured if I'm going to replace it, I might as well go up to a 2" and go stainless. I guess I was just curious that if I DID get a header and 2" piping for the +3 HP, if it would be negated by the use of an OEM Muffler.

But I like your idea of cutting the flange off the oem muffler, resizing the inlet to 2" and welding a new one in.

Unless your state is strict on emissions, then you can remove the cat and have no CEL using an O2 sensor cheater (it's a kind of bung that's welded into your exhaust) that keeps your O2 sensor happy so that it doesn't throw CEL. Cats are very restrictive, not even high-flow cats are good. (I used to believe the hype about high-flow cats until I tried it for myself).

No matter how many cells per inch they have, they're still a wall that breaks up exhaust flow. Their flaw is in how they're designed to operate.

Anyways if you MUST use a main cat, a high-flow cat is better than the OEM cat, but it's still a cat is what I'm trying to say.

As for the second cat, you can trick your ECU into believing the mixture "smells" nice.

That is, of course, if you don't have visual inspection.... (gladly where I live they could care less haha)

Stock mufflers are terribly restrictive, not so much size but what's inside them.

Here's a cutaway of a stock muffler off a Mazda 626, probably very similar to what'd be on our cars.


Then here's a cutaway of a Magnaflow muffler.


Obviously a straight path is better than the maze that is OEM mufflers.

This post has been edited by Box: Aug 21, 2012 - 1:20 PM

cat can go byebye and not have the 2nd o2 at all