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so basically i have a universal muffler on my 04 civic right now and its a little loud but anything is better than stock...so basically i was wondering what size pipping i would need to get the right air flow to muffler (which would start right after the catalytic convertor)in order to make it to a custom whole exhaust setup like a greddy exhaust system or something of the sort...

 
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thanks for any and all input

 
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2.25 inch is usually the max i would go with for a civic.

 
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its more or less irrelevant what you got from the cat back. The downpipe is double walled.... so you're fooled into thinking its 2.25" but its really 1.75. There's a ring in the back of the cat which reduces the outlet to 1 7/8" to mate to the stock exhaust. Unless you get all that crap out of the way, there's no point in putting a bigger pipe behind it.

 
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this is 100% correct, your exhaust can only flow at its smallest diameter. unless your going to do an entire exhaust from the cat back its not going to make a difference. if i can suggest something. i have had a lot of experience with exhaust sizing. i actually work for a performance company as well. we mainly specialize in diesel performance but ne how. i think 2.25" is too big on our cars. that is unless you have some serious work done. 2" should be more than sufficient. the stock piping is 1.75" and increasing the dia .25" is plenty. this will allow you to keep some bottom end as well as open up the top end some. the gains on the top end may not be as big but you will retain your bottom end trq. this is what hondas lack, bottom end.

 
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^^^^ I believe you mean to say "from the header back", but double check it. You otherwise added more correctness to my correctness.

 
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i should have clarified a little better, the ex models should be from the manifold back, otherwise the lx /dx models have the cat incorporated in to the manifold which would essentially be a cat abck system. that is where that came from. i have an lx so when i spoke about cat back that is what i reffered to.....

 
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just becuz the header...or headers in ur case...are small doesnt mean they restrict anything. opening up our headers to a bigger size doesnt do anything but lose bottom end anyway. im putting my factory header back on cuz i painted it black and it looks cool. the dc sports is the only header out there the will SMOOTH OUT the power band, still no increase really.. barely anything. other than that if u want sum serious flow, take out the cat and put a test pipe in from megan or something. itll be louder ull feel a difference with ur new custom piping. and hey ....do u think 2.25 is really too big? will keeping it at 2" not lose any bottom end? what will 2.25 do...advantages and disadvantages...anybody?

 
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depending on which edition you have will some what determine what size your exhaust pipe can be. If's it the EX then you have to worry about the cat and how to weld ends that will work with you stock cat. I got a LX and I run a 2 in because any my car is almost scrapping the ground when I drive.

 
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i had a complete 2.25" system, dc header, random tech cat, and greddy evo2 exhaust. i lost bottom end.... i gained some top end power but i would rather keep my bottom end since that is what this car lacks big time. what you actually gain in the top end going to a 2.25" isnt enough to warrant losing your bottom end.

 
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im pretty sure my model is a DX however mim not postive all i know is tha its an 04 civic VP which i understand has the same engine as a DX...so knowing that yall are suggesting a 2" piping welded right after the cat? and im not really looking for gains or losing anything eiter i just want to make my exhaust sound a little louder with the universal muffler that i already have on there.....perhaps?

 
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take out the resonator and increse diameter of piping to 2" you should be satisfied with performance and sound

 
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i beg to differ...

no offense, but its probably ricers like with with ur exhast mind set that givs us a bad name....a shitty exhaust is not worth it.

 
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speaking of loud exhausts, my mexican neighbor has a 92 honda accord. and he recently got 3 inch piping from the cat to a huge 4 inch stainless steel muffler with no resonator. that thing is so freaking loud, i can hear it from 3 miles away. and he always revs at me, when i'm outside working on my car and i just incessantly laugh at him when he does. damn ricers, they need to smacked upside their heads

 
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I went Magnaflow on my last car (4.6L V8) and with this car. I don't regret it ONE bit.

I bought the Magnaflow catback, installed it, and let the good times roll. Sounds great when I hammer it, low drone, and quiet idle.

So I say buy a Magnaflow catback. It will give you what you want without sounding like some of the Honda's that roll around town with cheap exhaust.