Just in case you wanted to know what they look like...

 

wow, looks very restrictive. haha

 

Hahaha, thanks, I've been wanting to cut one open for awhile.

As a matter of fact, the stock muffler (cat-back) is very restrictive, albeit quiet. It is much more restrictive than the FD main cat/midpipe and flows similar to the stock precat/downpipe. Yuk.

The point here is if you're looking for performance, the stock cat-back should be the second exhaust piece to be replaced--the first, of course, is the stock precat/downpipe. If you need a cat, keep the stock main cat as it is actually fairly high flowing, even with its 2-1/2" pipes. The reason for this is that it has high quality catalyst bricks that have a rather large cross-sectional area--significantly larger than most aftermarket 'high flow' cats.

 

+1. I think only replacin the back box will give you like +15hp

 

if its not in pure HP gain, you shave a bazillion ton of your car.

 

Just took my stock backbox and cat off, they weight together like 50kg's

 

Harry Potter Chamber of Secrets

 

While the stock cat does have 2 1/2 inch pipes, the flange welds reduce the front and rear openings to about 2 1/8 inches. Do the math: The opening area of a 2 1/2 inch pipe is 4.906 inches. The opening area of a 2 1/8 inch pipe is 3.544 inches. That's a 38% difference. I welded both flanges on the outside, then ground down the inside welds to the full 2 1/2 inches. I could feel a difference in performance with my new "higher flow" stock cat.

That picture of the stock catback is very revealing. Thanks for posting it.

 

Ivan and I took a hammer to a dead muffler to see what was in it, and the outer skin is just thin gauge metal, and so are the baffles, the only substantial parts are the front and rear ends which are either cast or machined.

 

Very cool photo. Was there any sort of material stuffed inside or was it hollow as shown in the photo?

 

pretty crazy

 

Until I saw an episode of "How it's made", I always these were stuffed with something, but it was just as you see it.

 

Thanks for this pics

I always want to open it to made some mod to it inside! Where i live i can change the stock exhaust for a free flow so i will open it to modified the inside like this:

 

Yeah it's a muffler. Congrats.