2.25 inch vs 2.5 inch custom piping.

I heard that 2.25 inch piping gives more low-end power.
and 2.5 gives more high-end power.
Is this true?
Is there much of a difference?
I also have a stock catalytic converter. What size diameter does it have?
When I do the custom piping should i change the catalytic converter?

the 2.25" piping is ideal for most hondas/acuras becuase they rely on back-pressure to work correctly, when you step up to 2.5" or bigger that is usually for Forced induction cars, becuase they have more power and more gases to exit from the combustion chamber. 2.25" is the highest a normally apspirated car should have on it, to gain the most power with minimal loss overall(did that make sense?).

As far as the cat goes, it is prolly around 1.5 - 2.0" range and for max performance out of your exhuast it should be replaced by a high flow unit to fit the rest of the new pipe work. There are notcible gains from installing a new exhuast system expect about a 7-10hp increase at the wheels with the installation of the new highflow cat and exhuast system.

Yeah, unless you have FI do not go larger than 2.25, and if you are getting it custom dome, make sure they use mandrel bent stainless steal piping. As far as the cat, make sure you get a smog legal high Flow Cat if you wanna pass emmissions/carb tesing or whatever it is where you are from.

If you know how to turn a wrench and don't mind getting dirty once a year I would say get a test pipe and when emissions rolls around swap you stock cat back on. Get the test pipe to fit your model car so its the same size as your stock cat and have your exhaust guy build from there. Even the free flowing cats have problem passing emissions(becasue they can't make up for a bad tuned car the way a stock cat can). This way you can save yourself some $$ on those expensive free flow cats and the test pipe will yeild more HP. Also if you are getting a custom set-up i would look into an adjustable muffler.

and mandrel bent is the only way to go(stainless is dependant on you budget)

good look man

So I should get race cat?
Will people off the streets know i have a racing cat?
Or do you have to go underneath to find out?
Does it make a louder noise?
I heard that someone put on a race cat and when he got out of his car he can smell gas fumes.


How much more is stainless steel?

stick with the stock cat, since your car is still relatively new and also high flow cats are very expensive.
cats shouldnt make it any louder, its the exhaust tip and they shouldnt be making the car smell like gas either.
u cant tell a high flow cat from a stock cat, they usually look alike.

listen to the other guys, use 2.25inch mandrel bend stainless steel. it is more expensive but its worth it.
stainless steel lasts upto 10 years whereas mild steel lasts upto 5 years.

Originally posted by asnrefugee
How much more is stainless steel?

Fair priced enough to be worth it. You do not want that shit to all rust up and all. IMO anyways.

The low down to the first question.
A bigger exhaust does give more top end and smaller exhaust bottom end (but not to small). A longer intake is good for bottom end and short intakes for top end.
If you have extractors on your car the exhaust has to be of size not to big so that the pulsation of the gases is kept in motion through the extractors other wise a to bigger exhaust system can actually repead the gases the extractors are attempting to flow.

Good sizes (average) 1.0lt - 1.6 1.75 inch for 1.6 - 1.8lt 2 inch, 2.0lt - 2.3lt 2.25 inch for 2.2lt vtec engines 2.25 or 2.5 inch.
Madrel bends YES. Stainless??? All mufflers, cats etc in stainless but the piping will last ten years easy in mild steel even longer with a high temp coating.

All the best:flash:

What is the orignal size of the factory piping?

somewhere between 1.75 in to 2.25 inch most probably

Grab out a tape measurer or ruler and find out.
But on your car I'd say its either 1.5 or 1.75inch depends if its vtec or not.
If its not go for 2inch and if it is go for 2 or 2.25 inch.
:flash:

So if I have a D16Y7 (Civic DX) motor, then I should go with the "2 inch piping, verses the "typical" "2.25 piping? Remember, 1.6l NON VTEC here.

MARKUSIUDIUS: when you said a longer intake is good for low end, and a shorter for high end, did you mean a Cold Air intake is better for low end increase and a short ram intake is better for high end increase? That was something I never new if that is what you meant. :bloated:

On a 1.6lt motor a good 2 inch system will flow just as much as 2.1/4 inch and without the noise.

Long intake is yes, better for bottom end and a shorter for top end.
Within reason.

A filter under the factory airboxwill give better bottom end then one at the throttle face, but will loose in the top end stakes.
Its much like short and long intake runners.

Before I installed my blower I used to have twin throttle bodie set up. It was a second throttle face tapped into the rear of the factory throttle bodie to come on at different adjusted times. The first one had the standard intake piping with a pod filter on the end and the second had a filter right at the throttle mouth. As you accelerated the first would open for bottom end and at about 2/3 of full throttle the second would snap on for top end power.
On the dyno the top end power was only about 5hp at the wheels more than with the standard throttle and pod setup but it had a better power curve from start to finish. It with only a few other mods was good for constant mid to high 14s.

But then I seen the light.
:flash: