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I recently put a Greddy EVO2 Cat Back Exhaust on my 2003 CiVic EX. I am actually losing horsepower because of the lack of back pressure. It also rattles a little. It was up on the lift the other day and there is more than an inch clearence on the pipe. three people where shaking and pushing on it and could not get it to hit the underbody. Please help Headache gettin worse?

 
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Did you check the torque of the bolts on the piping? Check for exhaust leaks in the piping.

 
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damn green beat me to it. Yeah you more than likely have a leak somewhere. And the rattling is either normal or it is hitting your bumper.

 
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if you still have a cat, there should be no problem with loss of back pressure through the muffler.

also, make sure your not hitting the body with the pipe, that kind of banging could trigger knock retard and cost you your power-

 
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the Evo II makes contact with the underbody right underneath the shifter. I put 4 layers of heat resistant fabric between the pipe and the car, and I have no more rattles. I'm sure that's your problem.

 
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Yeah it could be touching the heat shield

As for the back pressure. yyou bourth an exhaust to getter flow. So the HP's will kick in at a higher rpm. If you are on a freeway or highway you can mash on the pedal and get better rpm/power response.

People have this same complaint with intakes too.

 
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Yeah I have just a rear section exhaust and can feel the loss of backpressure. It's common with any free-flowing exhaust.

 
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I have the evo 2 and its performance fells fine. for the rattling mine hits the heat sheild under the shifter with i start hitting alot of bumps making the car bounce.

 
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I've heard that adding a universal silencer will also give backpressure while lowering the sound. I might be trying one for my rear-section.