mAMG

Hi all,

I have a very bad exhaust drone at low rpm and its so annoying .. Exhaust mod are EC headers all cats delete except mufflers. Cats replaced with with 2.5-3" striaght pipes ..

If i added a 3" xpipe would that eliminate the drone ?
Adding back resonaters or secondary cats is not an option.

euphoriaDSM

Forced fed cars should run a small H-pipe like the factory had rather than a X-pipe just to help with pulse scavenging and yes it will help with the drone.

trabots

I have the same set-up with no cats and just the factory cans all fed by shorty headers. I still have the cross-over after the 2nd cats. No drone at all, quiet at idle and cruise however full throttle is very unsociable, like a AA fueler.

cal1

Not sure what type shorty headers you have, but just wanted to point out that you might want to keep an eye on your air conditioner line that runs on the left side of the car. The insulation might start to flake off as a result of heat. I have Kleemann shorties and had this problem. I wrapped the line with some high heat material to protect it.

mAMG

Well, I found out that the factory H-pipe is still there. The drone exists at 1000-2000 rpm, and i can hear the exhaust pulses, even some time pops/crackles when downshifting ..

Also, the secondary cats replaced with a 2.5" pipe, resonators replaced with a 3" pipe i guess, while primary cats replaced with 3" ... Is that difference in pipe diameter makes a dramatic effect ? Should they all be changed to a 2.75" like OEM ?

Already ordered an x-pipe, should the H-pipe be deleted and replaced with X-pipe ? Or keep it and add X-pipe ?!

trabots

As the only real difference is that you have eliminated the forward resonator cans, I would put them back on as they do not restrict. That would put your car the same as mine so theoretically should eliminate your drone. I have used 3inch to replace the cats.

whatthe5

You can add in some non-OEM resonators... although I find not having converters to be a bigger noise problem on s/c cars.

Would recommend installing a high flow catalytic converter or two because it's better for you and environment and will sound way better with much smaller loss in power.

That or try something less traditional and have them build a small length of pipe and cap the end of that - helmholtz resonator style... can be very effective at removing resonant frequencies.

trabots

I am thinking of re-installing the rear cats just for their muffling. As noted above, taking the cats away takes most of the muffling away especially when having a squirt. Idle and cruise is great however.

B Feelgood

Try putting the OEM resonators back in their original spots. They are literally straight through with a perforated core and some some sound absorbing material within the shell if I remember correctly. Should help to dampen/soften your low end drone without affecting airflow or overall power.