if we can't find a way to crack the 5th gen ecu ..
i might go for a replacement higher flow cat..

do you think that the stock cat is restrictive enough to be worth investing on a higher flow cat ?

wich cat to buy ? wich not to ?
experiences ? flow numbers ?

anything that could help would be appreciated..and how much should i pay for a good?

thanks

 

The only way that a new cat is really going to make a difference is if your header and exhaust diamters are larger than your 2.0" diameter cat openings.

For example, if you had a header with a 2.25" collector diamter and a cat back with 2.25" diamter piping, then your stock 2.0" cat is a bottleneck. You might gain 2-4hp (guessing) with a Carsound or other aftermarket cat with 2.25" openings.

Integra Type R owners seem to like to upgrade the cat for the gains. And it is a relatively cheap upgrade (sub $300). You don't hear about it too much on H22as though.
Andrew

 

i will be reaplacing the stock muffler with custom mandrel alum steel 2.5"OD piping..

i wasthinking on playing a little with the stock header..
what is the size of the exit of the stock header ?
collector to the cat ?

 

Stock exhaust piping is 2.0" from the header collector back. A larger diameter cat is not going to do you much good unless you switch to a header with a larger diameter collector.

Andrew

 

exhaust is the biggest bottleneck on H22A's

 

..are BS, plain and simple. They are cheap and their longevity reflects it, the catalytic elemnts in them are sub-par, and most of the time the cat blows out w/in a 1 year or so. Also, most ITR owners upgrade or rather remove their cats b/c they use the JDM ITR 4-1 header and the header has a 2.5 inch collector that cannot be accomadated by the OEM cat. Also, test pipes are another thing to consider when replacing the cat, buit only if your car doesn't need to be emmissions legal. One thing to remember is that you want the interior diameter of all you piping you be homogenous in diameter, hence the advent of mandrel bending, if you replace the stock cat w/ one of much larger interior diameter you will effectivly kill the exhaust gas velocity and you will induce a bottleneck in your exhaust system, which is obviously bad.
If you cat is already blown out, then replace it w/ one that suits and retains the same interior diameter of your exhaust system, but dont take off and replace a perfectly good cat, just to put another one on w/out reason.

 

Please correct me if I am wrong, but I have been taught that in the 'hot' portion of the exhaust system velocity is very important for the scaveging effect of the header. However, after that the bottom line is a reduction in restriction (lower the better). I have also been taught that there is no reason to increase the size of your exhaust pipe any larger than the size of the collector. My question is how good is the stock header and even if you had a header with a larger collector would our wonderful OBDII tune out the advantage?

 

you guys are making me rethink all my exhaust plans now ..
eheh

i seriously thought the diameter of the collector was more than 2"
...
by the way, if any increase in diameter in the piping a kill for the exhaust flow..why do mugen still let a Resonnator on their mufflers ?
same with most aftermarket company..

mmm

what would be the best exhaust system design ? what are we looking for here ?


i am not sure that all i got wil work good now..
i already have buy a twin pass muffler with 2.5" piping all the way trough..

i know that a lot of power can be regained using good aftermarket cat backs..

like the GReddy EVO that we tested in our lude club...gained almost 10P at peak on a otherwise complete stock 2001 lude..
and gaved a little boost all over the rpms ...

and that is still using the stock cat ...
with a 2.5" piping all the ay to the back ..
...

i wonder if any work could be done on the collector to have it go a little smoother..
??

what are we looking at here with all that beeing said ?

 

..hot gases do travel faster, however another factor is the size and shape of the chamber that they are flowing through. If you have gases flowing at a constant velocity, they flow at that velocity into a larger opening they will slow down.

 

yeah i know..that's how it works...
that's why mandrel bent flows better cause it's constant diam ..

but for street use we need resonnator to trap some of hte sound without harming too much the flow..


so ..mmm if the resonnator is farther from the headers, it will not harm the flow as much cause the temp will had time to fall some .. ?? what do you think ?

...

...then if the diameter of the collector is 2" and the piping after the cat is 2.5"...
it will help to pass gaz cause the gazes get reallly hot passing trhough the cat for the 2nd time..
and then as they exit they need more space ...and neway once the exhaust lines are full of gazes the effect is less.
...

grr..
neway it is 100% sure that getting a higher flow muffler with a biger piping catback helps the power ...been dynoed few times..

the only part left is is it worth to do some work or change some parts in the collector to cat area ..

i myself can't change header cause of racing classe restrictions..but no rules against modyfying the stock one if it doesn't remove too much weight..
same thing for cat ..

 

I don't think exhaust gasses get hotter in the cat...do they. If so then a larger outlet would be bennificial. If the transition to a larger diameter is smooth you will not increase restriction. If it is flanged then you will create additional turbulance and thus restriction. The fact that the gas slows down is not an issue beyond the header as long as the restriction is minimized. as the gas cools down in the pipe it by definition gets more dense and the velocity decreases. If you want constant velocity you would have to gradually decrease the size of the exhaust pipe. Massflow is much more important than volumetric flow as far as the engine is concered. The same basic principal applies to the intake. Dense fast air is better because it has more air (on a mass basis) for conbustion.

 

the exact smae thing happens i think when the gazes go through the headers..

exits trough 4 generous ports..merge into 1 or 2 tubes that have less volume than the precedents..and so on to the collector..

so to keep the velocity at max we would have to use diminishing diameter exhaust that approx match the temp degradation of the gazes..mmm ..
that would be feseable using 2.5" piping for start and getting smaller piping 2-3 times during the exhaust way .. but neway i already have my muffler at 2.5" ;p

mmm...all that said, it still doesn't help that much with what to do between the header and the piping

 

Definatly NOT the same thing in the header. The diameter and length of all of the sections of the header are specifically engineered for the motor it is in and in fact tuned to be optimized at a specific RPM. This is why some headers have great top-end (peak) gains but actually hurt performance EVERYWHERE else. Others that are truly engineered for broad applications will give you gains through most of the RPM range. You wouldn't want to decrease the pipe diameter, because if you did it the way you are talking about the restriction you are introducing by a rapid change down in size will offset the very small gain you might get from a _continuous_ reduction in size. All moot with OBDII anyway. Unless you reset the ECU everytime you drive

 

hey hey
okok ..

LudeLC: why don't u give us your thoughts on what could be done to improve the exhaust system without changing the headers ??
that would be nice
heeh

 

Ok... I'll give you my opinion based on the assumtion there are no emmissions restricions.

1. If you want better low end performance extend the length of the collector with the same diameter pipe. If you want better top end shorten the collector. A industrious individual could do some research and "tune" the header to a specific range of RPM.

2. Let the collector exit to the atmosphere

If you have emmissions concerns or race division concerns remove as much restricion as possible after the collector.