importdreamer

I have a 98 Civic Ex. Its got a 2.25inch cat back to a ractive can. I'm debating on whether to get a hi-flow cat or headers. I was under the impression that i cant have both becuase it would kill the backpressure and result in a loss of power. The price of a hi-flow cat is way lower than the price of some decent brand name headers. Also loudness is a another thing to look out for, and I'm not sure which would be louder.

Ricey McRicerton

Backpressure IS NOT good for motors.

If you want to buy one single header to put on your car go for it. I refuse to buy a high flow catalytic converter for the single fact that they all seem to die and break up after about a year of use.

importdreamer

Don't you have to have SOME back pressure in order to help push out the exhaust thus helping the engine breathe? If the exhaust is just wide open all the way back the stuff just kinda hangs out and chokes the engine. Hence, your not supposed to put bigger than 2.25inch exhaust piping on a N/A civc.

Ricey McRicerton

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by importdreamer &raquo;</TD></TR><TR><TD CLASS="quote">Don't you have to have SOME back pressure in order to help push out the exhaust thus helping the engine breathe? If the exhaust is just wide open all the way back the stuff just kinda hangs out and chokes the engine. Hence, your not supposed to put bigger than 2.25inch exhaust piping on a N/A civc.</TD></TR></TABLE>

Why do people run open header at the track? Because it makes the car faster.

Why don't people run open header all the time? Because it's just too loud.

importdreamer

So why not get both in order to keep as close to legal as possible?

Ricey McRicerton

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by importdreamer &raquo;</TD></TR><TR><TD CLASS="quote">So why not get both in order to keep as close to legal as possible? </TD></TR></TABLE>

Feel free. As long as you get a header with a CARB no. on it, you'll be fine (even in CA). I don't know if there are any CARB legal high flow cats, but I know that I've yet to be impressed with any aftermarket high flow cats.

BauleyCivic

Headers, def.

importdreamer

I was worried that opening up the exhaust then cramming it in the cat and then opening exhaust again would just cause some problems. Should I hollow out the cat then? (by the way your civic is tight Bauley)

jlsmi2

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by importdreamer &raquo;</TD></TR><TR><TD CLASS="quote"> Hence, your not supposed to put bigger than 2.25inch exhaust piping on a N/A civc.</TD></TR></TABLE>

Where have you been getting this nonsense? Do a search for exhaust or cat-back and I think you'll find that 2.5" is probably the most popular size for n/a b-series civics.

If you have an ex, w/ d-series engine then you probably wouldn't notice much of a difference b/n 2.25" and 2.5" either way.

If you are going to stick with d-series then buy a header. No sense in upgrading your exhaust if you plan to put a b, h, k series engine in your car, would be a waste.

As far as high flow cats, I haven't had mine for a year yet, but no probs so far. Try to get hold of a Carsound (Magnaflow) they make excellent high flow cats. If you're sticking with 2.25" catback then get the same size converter. kteller.com offers a variety of bolt up flanged cats w/bung holes for ob2 if necessary that will go from your header/manifold to the exhaust system.

jlsmi2

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Ricey McRicerton &raquo;</TD></TR><TR><TD CLASS="quote">
Why don't people run open header all the time? Because it's just too loud. </TD></TR></TABLE>


...C02 kills people.

civiccpedx

well don't you need to have some back pressure?

99hatch

i ran open header one time cause my exhaust rusted off, but it was really boggy and didnt feel like it had any power at all. i thought when you ran without exhause you run the risk of damaging your engine?

jlsmi2

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by importdreamer &raquo;</TD></TR><TR><TD CLASS="quote">I was worried that opening up the exhaust then cramming it in the cat and then opening exhaust again would just cause some problems. </TD></TR></TABLE>


Shouldn't cause "problems" it just won't perform any better. The exhaust flow is determined by its smallest part. So if your manifolds collector is smaller than the cat/exhaust it will only allow that amount to flow out anyway.

Ultimately what you should do if you want better flow is get a header with a 2.25" collector, a 2.25" high flow cat (or straight pipe if you so desire), and match it to your exhaust system. Then you will have a full 2.25" exhaust.

If you get a header and then install a smaller converter you will cork your flow potential to the size of the cat.

00Red_SiR

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by importdreamer &raquo;</TD></TR><TR><TD CLASS="quote">Don't you have to have SOME back pressure in order to help push out the exhaust thus helping the engine breathe? If the exhaust is just wide open all the way back the stuff just kinda hangs out and chokes the engine. Hence, your not supposed to put bigger than 2.25inch exhaust piping on a N/A civc.</TD></TR></TABLE>

You are correct to think that it is important to have some back pressure in the exhaust for a NA motor. Back pressure helps keep exhaust gas velocity up especially at lower RPM which will enhance torque. Too much back pressure from an overly restrictive exhaust will cost HP especially in the upper RPM.

Like an exhaust system, porting a head a little over stock (going to a 2.25" exhaust) helps to reduce restriction and increase airflow making more power. Over porting a head (going to a 3+" or open exhaust) will really reduce restriction but it will decrease velocity and the car will make less power except at very high RPM. This is a perfect example of why bigger is not always better...it kills velocity.

In a car that's running a turbo, eliminating back pressure is ideal because it allows the turbo to spool up faster and build power quicker. The rules of maintaining velocity don't really apply because the engine is being force fed the air so velocity is generated and maintained from another source.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by importdreamer &raquo;</TD></TR><TR><TD CLASS="quote">I have a 98 Civic Ex. Its got a 2.25inch cat back to a ractive can. I'm debating on whether to get a hi-flow cat or headers. I was under the impression that i cant have both becuase it would kill the back pressure and result in a loss of power. The price of a hi-flow cat is way lower than the price of some decent brand name headers. Also loudness is a another thing to look out for, and I'm not sure which would be louder.</TD></TR></TABLE>

The stock manifold on the EX isn't that restrictive because it doesn't have the stock cat in the middle of it. Factory cats that are down under the car aren't that restrictive unless you're making big power, run at high RPM regularly or are boosting. The rule of thumb with exhaust tuning is that the farther away from the exhaust port the "restriction" is, the less of an (negative) effect it will have on power. By replacing your cat-back with a 2.25" exhaust you've reduced the most restrictive part of the exhaust on a Honda, which is the muffler (only the cat in the manifold is more restrictive). Unless you plan on really upping the power output a great deal, I'd just keep your stock converter for now since it's 2" in-out, and go with a DC 4-2-1 header. A good air intake would benefit your car more since the stock system is by far the most restrictive part on the car period.

Jimmy

iTrader: (5)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BauleyCivic &raquo;</TD></TR><TR><TD CLASS="quote">Headers, def.</TD></TR></TABLE>

Heade<FONT COLOR="red">r</FONT>

McNizzle

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Jimmy &raquo;</TD></TR><TR><TD CLASS="quote">

Heade<FONT COLOR="red">r</FONT>

</TD></TR></TABLE>

thank you

b16spaz

i would deff say headers cause i used to have an aftermarket cat and the o2 sensor hole was in the wrong possition and raddled, and dident feel much more power, so now im back to stock. btw the cat did make a noticable differance in sound

gSIr

I would deff say header and not a cat. If you get both, you can reduce backpressure and power. Without some backpressure the car will lose low end power and the exhaust gases will have a lower velocity and will remain in the engine longer, which could burn the exhaust valves. People that are turbo run open headers because the turbo itself creates enough backpressure for the exhaust, as for the people that are NA, they do that because they run at such high rpms at the track.

93egSIboi

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by gSIr &raquo;</TD></TR><TR><TD CLASS="quote">I would deff say header and not a cat. If you get both, you can reduce backpressure and power. Without some backpressure the car will lose low end power and the exhaust gases will have a lower velocity and will remain in the engine longer, which could burn the exhaust valves. People that are turbo run open headers because the turbo itself creates enough backpressure for the exhaust, as for the people that are NA, they do that because they run at such high rpms at the track. </TD></TR></TABLE>

Ive heard that running with open header and little or no backpressure for an extended period of time messes up you valve alignment bad. So unless you want to adjust your valves every week you probably shouldn't run open header, plus its facking loud and annoying, and also doesn't do the enviornment that much good either.

Del Sol SiR

iTrader: (2)

I recently installed a Catco hi flow cat to pass smog in CA, n I passed. Was a + difference from the blown cat that I was using.

dantastic

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by jlsmi2 &raquo;</TD></TR><TR><TD CLASS="quote">...C02 kills people.</TD></TR></TABLE>

yea if you're in a room full of it. CO2 is controlled mostly b/c it's a green house gas, contributes to urban smog, and disrupts the carbon/acid cycle.

just beware that many of the "hi-flow" cats out there aren't realy cats at all. they're just test pipes with resonators on them. if you have an OBD2 car (which you do), it'll throw a check engine light b/c your "hi-flow" cat isn't doing anything. however, there are hi-flow cats that are real cats, like catco and magnaflow. they do work like normal cats and you will still probably pass emissions.

aftermarket cats tend to fail quickly though. i've heard of them dying after just a year.