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hey, i have a 01 ex. and im planning on putting a DC sports stainless steel header and a apexi world sport 2 catback exhaust. should i put a highflo cat also? and was wondering what kind of hp gain do you think ill be getting? thanks

 
Rep Power: 231

from your dc header and the apexi catback, youre looking at a gain of maybe 3 hp or so. if you want any extra gains you should replace your downpipe as well (i would suggest the random-tech downpipe with high-flow cat). without replacing your downipe (with cat on it), you are somewhat 'choking' the system.

imagine your header flowing smooth, stock downpipe restricting airflow, and catback flowing smooth, youd get a sort of system like in traffic. 3 lanes of traffic being forced into 2 lanes, then allowed to open up again into 3 lanes.

even by adding the high flow res/downpipe, it will still only get you an extra maybe 1.5-2hp though.

 
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i wouldnt say it would only give 3hp. i dynod mine on a chassis dyno w. a i/h/e and stock replacement cat and i put 115whp and 104tq.

 
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ok thanks thats all i was wonderin for now. i also plan on putting a cai to help open things up. something to help with low range power.

 
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im confused. you said you put out 115 whp, is that not LESS than stock on your 03 ex?

 
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When i dynod my car i only got 105whp i think something weak like that lol but i have dx and it was stock when I did that.

 
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no a stock ex has 127hp to the crank. 115 i made is to the wheels which is pretty good for a civic w. bolt ons

 
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At the wheels, a stock civic only has between 90-95hp... Dealers rate them at the crank because they get a higher number. On my LX with aem v2, stock EX header and stock EX downpipe, and a DC TCS exahust I made 107 (numbers in sig). Thats 12-17 hp increase with the STOCK cat and STOCK downpipe. I really dont think you'll make more power with a high flow cat. Dyno before and after you replace it to see if its worth keeping.

 
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The cat does not really restrict anything at all so you do not have to worry bout that. And the the 127 hp is to the crank not the wheels. The power to the wheels is all you need to worry about. Take the power to your wheels and times that by 15% drivetrain power loss and minus that from the original hp. And that is a rough estimate. It all depends on how good you treat your car and what octane you use to.

 
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octane doesn't matter on a stock civic or with i/h/e.

 
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im now runnin a custom high flow cat. it feel like it has more torque but i havent had the chance to go back to dyno it again. hoping to go back sumtime in the summer.