Have a cut off wheel, a sawzall and a welder, but no money to spend on a nice exhaust?

Then this mod is for you!

I just couldn't justify spending 300 - 600 on a cat back, so I started making my own

We used to do this to the stock mufflers on evos, worked really well and had a nice stealth look.


First I cut open a stock s4 turbo II muffler pretty much completely. Here is what we find inside:




Hmm that looks restrictive. Lets remove the major restrictions!




That should flow better, plus... It's lighter!

Here is all you really need to cut open, second one was a lot easier:




I suck at welding thin metal, and this metal is very thin... oh well no one sees it. Probably be a lot easier with a gas mig (using flux core) or a 110v mig.





Noise is up a little bit, not much. Sounds good.

Power is up, boost response and spool time has improved, peaking the same but holding boost better to redline. Keep in mind that this is with my 1jzgte but should have the same kind of good results with any engine.

Love it, hate it - it was free power.

 

Nice . Never seen the inside of a stock muffler before. I wonder if I could do anything interesting with my old n/a mufflers, they're basically worthlass anyway.

 

im sure they are nearly the same inside.

 

Im going to make a 3 inch cat back when my 3 inch y pipe i ordered gets here

 

I just made 285 whp through them. with almost no sound!

 

What a strange design to cut noise down. It still looks super restrictive even with the innards cut out.

 

The typical muffler uses chambers of specific volumes / lengths so that the sound waves bounce back and cancel eachother out. The lengths are matched to the wavelengths of the sound they want to cancel. The problem is all this direction changing eats power. Modern mufflers are better about the restriction.

 

The stock evo 8 muffler actually has a spring loaded door that opens when you get on it, making the muffler a straight through design. We used to weld the doors open and pick up a lot of lowend and about 10whp peak with just that. Still were quiet though.

Overall the sound is a little too quiet and restrictive for me. I know there is probably 10-20 whp if I put some cans on.... but I dont want that much noise and the cop attention. Looks stock right now :P