I have a 99 civic ex coupe and am planning on buying a new 4-1 dc header. anyways i was wondering how much difference will there be if i get it port and polished and how much will that cost? is it worth it

 

not a noticable difference if the valvtrain is stock. biggest difference you might notice is a slight increase in gas milage and throttle response. slap a cam in there and itll make a difference depending on the type of porting done.

 

I've heard gains of 30HP with a P&P, but that is prolly with upgraded cams, valves, retainers, etc. If you are going to get a P&P you are going to want to get a valve job where they make the hole for the valve bigger. While you have it apart you might as well change the valve train compenents. It isn't cheap, like 1k for a good job.