If i hollow out my cat will it throw the CEL

[Slammed Accord]

ok, my cat converter is bad.. since i dont worry about smogging the car, my question is will the car throw a cel light if it is hollowed out ?? or is there anything i should worry about by hollowing it out ??

[BIGsnorlax]

\ is there anything i should worry about by hollowing it out ??

the environment

[brsteinbach]

Biotch ^. J/K. No it will not throw any codes. It will make your exhaust louder tho.

[Nurega]

Title on front page is creepy. "If I hollow out my cat..."

Anyway, it really shouldn't throw a CEL. Removing the innards of the cat would reduce back pressure, but I really can't see any reason for the CEL to trigger. Perhaps a more experienced member will have a better answer.

[visualpoet]

Your car will never know. All the sensors are upstream of the cat on our cars, so they won't be affected at all.

[ssondubs]

I have the "megan racing test pipe" in mine that I use in between emissions test. It won't cause a trtrouble code since our cars are pre-obd2 so no o2 sensor after the cat. Pros are more power at a higher rpm, mpg gain and a noticeable increase and sound. Cons are noticeable increase in sound and nauseous feeling from smelling all the fumes from the missing cat.

[kouzie]

Before I have just header, test pipe, and cat back mine throw a cel which was my old setup.

[Brandoncb7]

What's your reason for wanting to hollow it out? Nice Banshee if it's yours. You might be looking at 1hp which isn't worth the work to hollow it out lol. You'd do it and have a stinky car that will probably smoke a little bit here and there. I'd honestly say don't so it. Who's the blonde?

[Slammed Accord]

thanks for the info.. i figured if it was bad anyhow i might as well just hollow it before it plugs up or starts to hinder to motor.. after thinking about probabally wont make things any better.. i just remembered back to my first lowered truck where the cat completely plugged up.. so i hollowed it.. noise wasnt a concern as i had a straight pipe with a vw stinger on it.. boy the good old days.. so i guess i just wont mess with it.. as for the banshee.. yes its mine.. runs on methonol and nos.. the girl on the bike is my ex, porn star Amber Peach

[lowprofile]

thanks for the info.. i figured if it was bad anyhow i might as well just hollow it before it plugs up or starts to hinder to motor.. after thinking about probabally wont make things any better.. i just remembered back to my first lowered truck where the cat completely plugged up.. so i hollowed it.. noise wasnt a concern as i had a straight pipe with a vw stinger on it.. boy the good old days.. so i guess i just wont mess with it.. as for the banshee.. yes its mine.. runs on methonol and nos.. the girl on the bike is my ex, porn star Amber Peach

lol thats awsome. you will see a better increase with a test pipe ,expansion chambers are for two strokes you know, the hollow area will cause turbulance and i think you will lose top end

[deevergote]

Title on front page is creepy. "If I hollow out my cat..."

Anyway, it really shouldn't throw a CEL. Removing the innards of the cat would reduce back pressure, but I really can't see any reason for the CEL to trigger. Perhaps a more experienced member will have a better answer.

Removing the inside of the cat will INCREASE backpressure...

Come on man, you're an engineer in training! Put some brains into it! Creating an unnecessary open chamber in the exhaust piping will create significant turbulence in the exhaust flow. The exhaust swirling around in that hollowed out cat will act as a considerable restriction, and actually DECREASE performance. (damn, lowprofile beat me to it... )


Hollowing out your cat is one of the stupidest things you can do. The design of the stock cat is fairly free-flowing anyway. Just keep it. Plus, it keeps your car from smelling bad, polluting the environment, and sounding like crap.
If you want one that flows better, go to www.sms-products.com and get one from there. They have very free-flowing designs.

[Nurega]

Removing the inside of the cat will INCREASE backpressure...

Come on man, you're an engineer in training! Put some brains into it! Creating an unnecessary open chamber in the exhaust piping will create significant turbulence in the exhaust flow. The exhaust swirling around in that hollowed out cat will act as a considerable restriction, and actually DECREASE performance. (damn, lowprofile beat me to it... )

hmm. I've given this some thought, and here's my conclusion.
The catalyst is in the form of a packed bed in tube flow. The gas passing through it will be turbulent due to the packed bed (catalyst) being there; without the packed bed, the only factors contributing to turbulence are the expansion and contraction of the pipe. Because gas flow is turbulent in both cases, we're seeking to find which case is MORE turbulent than the other. Higher turbulence should entail higher back pressure. Since we don't know the specific characteristics of the exhaust flow (viscosity, velocity, density), I'm going to go ahead and assume that:
a) At open throttle with low revs, the exhaust's inertial forces are little enough that back pressure could be reduced, in comparison to the turbulent flow with the catalyst in place.
b) At open throttle with higher revs, the higher inertial force of the exhaust would create a more turbulent exhaust flow even without the catalyst material; it is more likely to increase resistance and thus, increase back pressure. Simply put, the added turbulence created by the expansion/contraction of the pipe will dominate over turbulence created by a catalyst.

So I think it's safe to say lowprofile and Deev are correct about increased back pressure, albeit when based on my two assumptions, only when the [hollow catalyst] exhaust's inertial forces are higher than those of the exhaust with the catalyst (packed bed). This is the case over a higher portion of the engine's operating range.
Sorry for the long diatribe, everybody. And Deev, I'm ashamed of what I posted earlier; thank you for calling me out on this one!

[drkshdw107]

good info guys...I actually gutted mine a few months ago just because it was clogged and giving me problems...and couldn't afford a new one at the time. And yes, the car is very stinky...I will be replacing it shortly...but I think i want to re-ring the engine first cause I am burning ALOT of oil...like 4-5 qts. per tank of fuel.

[1990Ex]

it will smell

it will suck on take off

feels good at higher speeds (but who drives around that fast alll the time )

car will sound like pure SHIT!!!!

[deevergote]

hmm. I've given this some thought, and here's my conclusion.
The catalyst is in the form of a packed bed in tube flow. The gas passing through it will be turbulent due to the packed bed (catalyst) being there; without the packed bed, the only factors contributing to turbulence are the expansion and contraction of the pipe. Because gas flow is turbulent in both cases, we're seeking to find which case is MORE turbulent than the other. Higher turbulence should entail higher back pressure. Since we don't know the specific characteristics of the exhaust flow (viscosity, velocity, density), I'm going to go ahead and assume that:
a) At open throttle with low revs, the exhaust's inertial forces are little enough that back pressure could be reduced, in comparison to the turbulent flow with the catalyst in place.
b) At open throttle with higher revs, the higher inertial force of the exhaust would create a more turbulent exhaust flow even without the catalyst material; it is more likely to increase resistance and thus, increase back pressure. Simply put, the added turbulence created by the expansion/contraction of the pipe will dominate over turbulence created by a catalyst.

So I think it's safe to say lowprofile and Deev are correct about increased back pressure, albeit when based on my two assumptions, only when the [hollow catalyst] exhaust's inertial forces are higher than those of the exhaust with the catalyst (packed bed). This is the case over a higher portion of the engine's operating range.
Sorry for the long diatribe, everybody. And Deev, I'm ashamed of what I posted earlier; thank you for calling me out on this one!

I didn't mean it in a mean way... I just know what you're studying now

Keep in mind, the hollow cat wouldn't be a straight pipe. It would be a chamber. A wider section of hollow pipe.