any one with a y-pipe ever have problem with it sounding like it's hitting something under the car?,under heavy acceleration there's a dull banging sound.

 

this is a common problem with the 3rd gens...our source is usually the sway bar...sign of either bad motor mounts or bar hangs to low (cattman)...your car is fairly new...i can't see the motor mounts being worn already

 

I have heard there is a bracket of sorts which causes the noise under heavy acceleration. The exhaust system, when taxed, moves and strikes the bracket. The bracket is not an issue under slow or normal driving.

Look at this write-up about a Y-pipe install:
http://integra.vtec.net/geeser/megamax/

Scroll down to "How-to install....", then choose "Y-pipe install", then choose "99-2K Cali Y-pipe(by Greg Prete)". Go to the bottom of the page, then go up three boxes and it speak of a "rattle" when it is "floored".

Hope this helps.

 

I had that problem when I first installed my Stillen Y. The bracket that supposed to attache to the body of the vehicle did match the original rubber hanger. I wasn't able to attached it because the holes didn't match up. THe hole in the hanger was approx. 1 inch to high so I left it un attached at first and removed the rubber part of the hanger. When I first started driving my car I felt a vibration that just wouldn't quit. Under harder acceleration it would give a thump or loud bang. I placed it back on the ramps and bent the bracket forward some. This helped but around 45 it would vibrate again. I finally just cut the bracket of and no more vibration or noise. Were you able to place the hanger back on the bracket at the middle of the Y-Pipe? If not this might be the problem. If you did check and see if it is banging the bottom of the floor. I email Stillen and never receive a responce so that is why I cut the bracket off of the Y-Pipe.