I have been searching the forum for posts concerning modifying the stock muffler on the '05 sedan. As I understand it, the system has two exhaust outlets, but they are both open only under hard acceleration.

Has anyone tried to drill out the valve or stick it in the open position to improve flow?

 

That would actually hurt performance. A little backpressure is good for making low end power. Smooth, open exhaust is, of course, good for top end. The factory muffler offers the best of both worlds.

 

I've heard arguments for and against backpressure. However, I agree with the backpressure argument when we're talking about N/A engines.

How much low end power are people losing by adding a midpipe and muffler or cat-back system?