How much HP are my stock cats robbing right now?

[KMeloney]

Hey all,

I recently put Corsa Ti's on my car, and I LOVE the sound. But reading lots of posts about people thinking their similar set up is too loud got me wondering: maybe the fact that I still have the stock cats on the car is really quieting the exhaust down -- and maybe they're robbing valuable HP, too.

I have TPIS long tubes (so the PRE-cats are gone) mated up to the stock cats, mated up to a full Corsa Ti (including it's H-pipe) system. I'm currently running the Corsa mufflers.

The car is quiet at cruise, and screams at WOT. The popping on deceleration is great. As I said, I love the sound. But I wonder if I would like it a hair LOUDER.

Should I ditch the stock cats for some aftermarket ones? How much HP are they robbing right now? Are they really quieting the system right now? (It's not quiet, trust me -- but the difference between my volume and others' appears to be the cats.) Are the stock cats enough of a bottleneck in the system right now that I'd FEEL a difference if I ditched them?

Any input would be appreciated! Thanks!

-Kirk

[NinjaZ06]

It is only from what I've heard, but anywhere between 5 and 10HP, by removing them completely. To replace them with aftermarket versions, it would seem as though it will go down from the 5 to 10.

[Sanford]

10 to 5..........

[JWSchmidt3]

Horsepower is hardly effected, but torque is much improved. I had a H/C package on my vert, and when we pulled the cats, I picked up 1 rwhp and 27 rwtq. It was loud though. I'm switching to hi-flo CATS this weekend, along with a smaller blower pulley.

[KMeloney]

Thanks for the replies, folks!

So then, would you say that if I like the SOUND the way it is now, that I ought to just leave well enough alone? Or, would you say that the 5-10 figure is substantial, and well worth the noise level increase (and installation efforts involved with adding aftermarket cats)?

Can the increase in torque be felt (without anything more than a Sidewinder intake getting more air in the engine)?

I guess I'd like to know whether you all would bother going to hi-flow cats at this point, or whether I should just leave the car as it is now. What would you do?

Thanks!

-Kirk

[mcss383]

I would say it comes down to if you plan on doing some more serious power mods later on. If you are planning on doing some form of power adder then definitely get some aftermarket cats on because it will be needed then. If you are not planning on doing any more major mods in the near future and you are happy with the sound then leave it be. Things like cat's have a HUGE effect on how the exhaust sounds so the change may give you a sound you do not like, or possibly one you would like even better.

[KMeloney]

Originally Posted by mcss383

Things like cat's have a HUGE effect on how the exhaust sounds so the change may give you a sound you do not like, or possibly one you would like even better.

Dangit. Herein lies the problem. LOL

So how exactly do aftermarket cats change the sound characteristics of the exhaust? Do they just make things louder? Or, more mellow? More raspy?

Also, if I get no resonance right now (I don't), then could hi-flow cats make it so I DO get resonance? (Or, is that cancellation more a function of the mufflers?)

Thanks again!

-Kirk

[mcss383]

The cancellation is from the mufflers mainly, but you could have a change in tone if the aftermarket cat is a different dimension and it will be louder. More likely then not you will still like the sound, but there is always a chance of it becoming too loud for you, different tone at idle, etc. If you want the exhaust to be louder I would say just go for it. It will be louder with an aftermarket cat and you get the benefit of a few extra ponies, but i wouldnt expect 10hp, maybe 5-7hp at best with your current power level. If you add more power in the future then the gains become more significant.

[OneQuickCoupe]

I have a heads and cam setup with increased compression and the same Corsa Ti system you are running, (W/mufflers). I pulled the cats when the system was installed. It is super loud and I mean the cops slow down and look at me loud with I drive it down the freeway. I had a set of Randoms installed last week and will pick it up this morning. Hope it toned it down some. You may like the sound without the cats but for me it's just too loud.

D.J.

[IVOZ06]

When I went to long tube headers with an off road x pipe and removed the cats altogether, with a Predator Custom Dyno tune I pulled a 38rwhp increase and that was through my stock TI.

It was loud at WOT but OK at idle, so I went with B&B Bullets and now I am a happy man.

Resonance, yes but controllable with rpm, you learn where it is and stay away. Also a Andy's Partition helped immensely

Oh yeah she is loud but I drove it around open headers a couple of days and that was a bit too much

"LOUD" is relative. What is loud to you maybe quiet too me.

I have read many posts on this subject and to some it has been too loud for them.

It is all trial and error, to see have much noise you like.

My dyno numbers are awesome for not having any internal mods. YET I am asking Santa for a cam

It is all what you would like and what makes you happy.

Like mcss383 wrote: "I would say it comes down to if you plan on doing some more serious power mods later on. If you are planning on doing some form of power adder then definitely get some aftermarket cats on because it will be needed then. If you are not planning on doing any more major mods in the near future and you are happy with the sound then leave it be. Things like cat's have a HUGE effect on how the exhaust sounds so the change may give you a sound you do not like, or possibly one you would like even better. "

Now go forth in peace my son and mod it like there is no tomorrow

[C5~Missle]

The stocks cats flow very well... Not worth the trouble to change them out for few HP..... besides... you need some back pressure for low end torque....
mike