Catback(Backpressure)

[240SX.SK]

I have a stock s14 and I'm replacing the muffler and I'm wondering if cutting out the cat is a good idea while I'm at it. Does anyone know if losing the backpressure will hurt my performance or enhance? 1/4 mile? Accel?

[ADAMHU]

it will help your top end power..though its illegal to do in quebec

[240SX.SK]

But will it hurt me off the line? Like will i lose alot of torque?

[JJ240]

Depends on how large it is. If it is large enough that your exhaust gasses lose velocity as they go through then yes it probably will hurt your low end. If it is the right size for exhaust gasses to flow through with little turbulence then it shouldnt hurt. Problem is sometimes theres less or more exhaust flowing through so its kind of impossible to have an exhaust that is perfect for every point in your cars powerband.

[Aries]

if the piping is larger than 2.25" you will lose on the low end due to the size of the stock exhaust manifold. The gases will flow out far too loosely, and you will not retain enogh backpressure to have good torque down low in an N/A car.

[Open4Cycle]

Back backpressure is not a friend to a 4 cycle engine! The reason that enlarging tubing can decrease performance is due to the fact that you are reducing velocity of escaping exaust gasses. A two stroke however relies on backpressure because the denser gasses create a better environment for sound pulses to travel in. A common method for using sound pulses to evacuate the cylinder of a 4 stroke is to use step tubed primary headers. At every step there will be a reverse pulse directed back inside the cylinder. The steps are located to return the pulse at correct timing events at certain RPM's. Using the step method also keeps the gasses flowing at a consistant velocity throughout the tubing. Now to answer the original question. You should notice an increase in power throught your power band by gutting the cat but I would replace it with a piece of tubing so that , well look at the shape of the cat and you decide why.I hope this helps.

[SSS]

Run a 2.5" cat and it should pose only a VERY low restriction if anything.

[240SX.SK]

You mean put in a new cat or replace with a piece of 2.5" pipe? I don't want to replace it, i want to remove it. REplacing it would kind of defeat the purpose I think. I've been told that I will get about 35% louder without a cat? Can anybody back this info up?

[SSS]

If it's illegal to do where you are (i know it is where i am) get your old cat converter, punch it out, and take it to an exhaust shop and have them run a pipe the same size as your catback through it; no one can tell any different unless they remove the car from the car. Or if you start running rich and have flames belching out the back....

[Bud]

You mean put in a new cat or replace with a piece of 2.5" pipe? I don't want to replace it, i want to remove it. REplacing it would kind of defeat the purpose I think. I've been told that I will get about 35% louder without a cat? Can anybody back this info up?

I just went from a test pipe and crappy midas catback to some stuff leftover from my turbo vw (3" HF Cat and 2.5" brullen universal muffler) and a custon 2.25" catcback. The test pipe didn't seem to make the car that loud, not with the resonator and muffler both courtesy of Mid-a$$. The sound now is not bad, kinda loud a WOT but I easily hear 10 cars a day that sound so much worse, good for the $100 bucks I paid for everything. I have to pull off the heat shield, it's buzzing at 3100 or so.

[sx=moresex]

I just went from a test pipe and crappy midas catback to some stuff leftover from my turbo vw (3" HF Cat and 2.5" brullen universal muffler) and a custon 2.25" catcback. The test pipe didn't seem to make the car that loud, not with the resonator and muffler both courtesy of Mid-a$$. The sound now is not bad, kinda loud a WOT but I easily hear 10 cars a day that sound so much worse, good for the $100 bucks I paid for everything. I have to pull off the heat shield, it's buzzing at 3100 or so.

i got a 91 ka24de i put on a custom dual exhaust strait pipe form the headers no cat(s) at all and yes its loud i have 2 "mufflers" if you wish to call them that along with a custom x pipe. but yes even with the mufflers and x pipe its loud at hell i love it

[TrunkMonkey]

i got a 91 ka24de i put on a custom dual exhaust strait pipe form the headers no cat(s) at all and yes its loud i have 2 "mufflers" if you wish to call them that along with a custom x pipe. but yes even with the mufflers and x pipe its loud at hell i love it

raise your hand if you see something wrong with this post.

-demetrius

[sx=moresex]

explain please

[float_6969]

I think he's making refrence to the dual exhaust on a 4 cylnder

[ralphyboy]

that would be alot of xtra weight for no reason also, I bet it looks cool though. An x-pipe is there on v-engines to equalize the pressure on each side an inline would not have to do that.

[project240racing]

I use the test pipe on my car........i found i lost noticable torque off the line but i thnk i may have gained top end

[Spec-R]

What would happen if i left the Cat on, but put in a 3in exhuast? would i loose alot of backpressure eventhough the cat is on??

[TomsMR2]

you absolutely 100% never want any back pressure. zero backpressure is optimal in all NA or turbo applications.

you dont "need" backpressure, you accept the performance loss of backpressure to gain velocity. while velocity is dependant on backpressure, backpressure isnt good.

ideally, you want to be in a backpressureless vacuume... ie: maximum velocity with zero BP.

with a cat and 3inch exhaust, you get the worst of both worlds. backpressure with low velocity...

[180sx]

did in on mine cut the hole pipe out and put a 3.5 inch piping from headerws streight to the muffler don't seeem to lose that much.

[drift240]

wat would be some good ideas for exhaust mods, other than the damn cat. convt. headers? any other?

[TomsMR2]

headers make the most power by far for exhaust mods.

theres just the header, the piping and the muffler.. theres not much else you can do.. unless you count the exhaust cam.