i installed my greddy evo cat-back about 2 weeks ago.. and i have an aem cai which has been on there for about 6 months. i had pulled the filter off the intake when i installed the exhaust to look at it see how clean it still was and it looked good. now my car will not go past 100mph .. now when it hits 100 my car sits around 5k and the speedometer sits at 100 for almost a minute.. then it will finally start slowly climbing. i figured it would have ran better w/ the new exhaust. any ideas?

 

This could be caused by gunning it uphill. Same happened to me with a DX SOHC motor. Try it on a straight surface or slightly downhill. Just a thought.

 

sounds like it's hitting limp mode - not sure why though - would need more info. Research resetting your ecu - good thing to do after any engine mods.

 

How big is your exhaust? Sounds like you've lost your back pressure.

 

i reset the ECU after i installed the exhaust, and i had done that when i installed the aem cai. it shouldnt be the piping size because a lot of people have the greddy evo.

 

bump.

 

Was it liked that before the new exhaust system? What kind of car is it & engine size?

 

wasn`t like that before the exhaust. 98 civic ex .. 1.6 sohc

 

What?! Back pressure is not good by any means. It only creates a quietter ride.
If you go over 2,5 inch you will loose air flow velocity, which is not very good, but wouldn't be extremely harmful.

 

Back pressure is a good thing for a naturally aspirated engine.

Each pulse of exhaust gas passing through the exhaust system creates a lower pressure area behind it, which helps "suck" along the next exhaust pulse behind it.

 

i have GReddy EVO exhaust and i havent had one problem wit it. its obviously a good echaust system so i doubt its the exhaust. but who knows

 

Oh my mistake. Sorry there I understood by "backpressure" positive psi building up in the exhaust because of the restrictiveness of the pipe, cause either by the bad bends or the insufficient diameter. You're right about the aspiration effect caused by each pulses. And it is diminished when you have a pipe with a larger diameter than necessary. The backpressure you're talking about is the negative psi following each pulse.