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7th Generation Civic In the years from 2001 to 2005 Honda released it's 7th Generation Civic. Chassis codes: EM2, ES1, EP3, EU1

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Old 11-26-2011   #1
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bypassing the catalytic converter

is bypassing the cat a good idea ? what's the horesepower gain of doing this ? can one run a valve controlled pipe in parallel to the cat without removing the cat ? so when the valve is open the back pressure is reduced and when the valve is closed everything goes through the cat. Any insights on this subject
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Old 11-26-2011   #2
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Re: bypassing the catalytic converter

The point of going without a cat is to reduce back pressure. It sounds like a good idea, but the air flow going from the headers to about after the flex pipe is the most important in reducing backpressure. the turns the exhaust has to take to bypass the cat would cause back pressure. the y pipe that you would fit in there would also caust back pressure no matter which path you have open because its not smooth.

Personally, I would weld in an lx downpipe with no cat, and then make the cat on the bypass pipe. a lot of work, but you could have an electronic switch when you get to a certain rpm so you could have good tq at low end and hp at high end. plus youd fool the emissions people XD
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Old 11-26-2011   #3
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Re: bypassing the catalytic converter

complete waste of time, and bad for your health
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Old 11-26-2011   #4
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Re: bypassing the catalytic converter

somewhere between 0.1 and 0.2 horse power gain on an otherwise stock engine, with an increase in emissions several fold.
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Old 11-26-2011   #5
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Re: bypassing the catalytic converter

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Originally Posted by gearbox View Post
complete waste of time, and bad for your health
agreed. if your that worried about back pressure get some headers and weld in a hi flow magnaflow cat.
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Old 11-27-2011   #6
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Re: bypassing the catalytic converter

1. Get an actuated valve. They start at about $60 and they look like this:
Click the image to open in full size.

2. Have the muffler shop weld it in the straight portion of the pipe in front of the cat. Should cost $50-100
Click the image to open in full size.


3. Wire it to a switch for the emissions test and those pesky officers.

Last edited by lazlong; 11-27-2011 at 12:09 AM.
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Old 11-27-2011   #7
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Re: bypassing the catalytic converter

most shops wont weld that in there...becasue "they can be fined" for bypassing it.

however good find. i didnt know such a thing existed, but still theres really no point becasue you wont feel any gain at all and would just be smoggin it up. now with headers and thicker pipes...maybe
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Old 11-27-2011   #8
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Re: bypassing the catalytic converter

hahaha!! WHY???!!!!! lmao!
So it will make 92fwhp?? LOLZ
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Old 11-27-2011   #9
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Re: bypassing the catalytic converter

better bet if youre worried about air flow is a muffler with valve that opens and closes depnding on how much exhaust is being pushed (based on engine rpm) like the rsx type-s jdm exhaust.
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Old 11-29-2011   #10
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Re: bypassing the catalytic converter

or just take the headers clean off and run it like that.
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Old 11-29-2011   #11
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Re: bypassing the catalytic converter

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Originally Posted by balzdpr View Post
or just take the headers clean off and run it like that.
lol do it
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Old 11-29-2011
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