Removing the resonator
 

Is there any reason to replace the OEM resonator with a straight pipe besides noise? It should lighten the car some. How about HP or increase air flow?

Super sprint makes a front pipe for the 540i and so does dynomax.

A mate took out the resonators and Cats on his 730 and straight piped the lot. It droned too much for him so he went and put Coby resonators back in and it sounds sweet now.

Again, the rear muffler is the one clogging up your sound and horsepower.

I got some suprsing gains with taking off mine. For 50 bucks I got some throttle response and it seems to revv quicker, not to mention that it has an awesome bark now.

Dude, that was the 1st thing I did when I bought my 540 1 week ago. My car is maybe a little quicker but the sound is incredible. I think it is perfect. I'm the type who hates droning or loud exhaust like in say a Mustang. My car now is pretty much silent now at highway speeds but has a noticeable deep growl while starting off. Not loud and not quiet. It really sounds like a toned down Viper or something. You should check it out if you want a little more sound out of your BMW.

Thanks for the tips. You guys should check out the multimedia forum. I linked some vids of guys with 540s and their exhausts.