Gutted cat

[DeathtoRice]

I gutted my cat today, and I didn't notice any difference other than it was louder and sounded like **** compared to how it did before. Am I just weird? Shouldn't I have noticed a decent gain in get up and go?

[1993blazerlt]

really gutting a cat will not do much unless the cat wa clogged before. The newer cats flow just fine. Now all you have is a place where the exausts expands and has to then be recompressed. The only way to gain any power would be to remove it all together

[DeathtoRice]

I have a piece of exhaust pipe thru the middle of the cat, so it is basically a straight thru system. I am going to get it done better when I get money tho...Cat has to be "there" so it will pass visual at emissions time. I was thinking about having a shop cut it in half from end to end, and welding the halfs back together over a straight thru system.

[bvr775]

You got mabey a 1/2 lb tq more and an unnoticable gain in the high end of the rpms. You have a honeycomb cat. They have almost no backpressor unlike the old pellet type cats that started the whole myth of gutting cats for gains.
you can't really gut a cat an exspect a gain anyway. What your doing is creating an exspansion chamber. It fills up with hot exhaust gas at the inlet cools and creats a bottle neck at outlet creating a more backpressor than you had before. you must remove the cat all together or build a fake cat(a cat caseing welding around a pipe).

If look at the new cats on trucks(2001-up in genrale and all 97-up gm vorteks) the inlet is slightly smaller than the outlet. The newly designed cat cause the air to flow out at slightly faster rate than it flows in. This creats a suction affect(not sure of the proper term) and is said in combination with a properly designed y-pipe to increase flow by 30%-35% over older exhaust systems.
for the vortec 4 banger owners a pacesetter header will create the same affect in combination with the stock cat

[Maximus]

I have to give my honest recent experiences with this issue.I recently bought a new cat to put on my S10 were I had cut the original one off a few years back.My original one was clogged so I removed it and used a straight pipe in to a 40 series Flowmaster muffler.Well my bottom end was hendered slightly with this.So instead of buying a new cat at the time used a small glasspack were the cat was before.I regained my lower end and it ran great.So a few weeks back I bought a new cat to replace the glasspack to see what it would do.Well it made a very noticeable loss in power over the glasspack.I left it alone for awhile to see how it effected the overall power band of the engine.Well it just sucked compared to the prior glasspack no matter what the RPM range was.So I took the cat back off and installed the glasspack again and to no suprise to me I regain my power I had lost with the cat.Now this is just speaking of my trucks setup but I will not be installing a cat on it any time soon.OK now to another experience but different vehicle,my TA.When I got it,it already had the Pacesetter headers SLP loudmouth exhaust but with a dynomax bullet in place of the SLP resonator and still retained the cats.I removed the bullet and replaced it with a Magna Flow race muffler.It didn't change the performance but the sound had a more throaty tone to it.So on a trial basis I decided to remove the cats and see how the performance would be effected.It made a decent improvement in the lower power band but made a very noticeable improvement in the top end power band.It gave it a even more throaty tone with out the cats.And just like my S10 I have not plans of reinstalling cats to it any time soon.Every vehicle is different and will respond differently to changes.In the case of my vehicles running no cats resulted in a performance gain.Again these are my results only and in someone elses vehicle it might not be the same.

[bvr775]

You've heard me say a thousand times that the new GM cat(2001 up) flows better than most cats out there. you want to know why. It has to do with amount of holes per sq inch in the honeycomb matirial and what the matirial is made of. I'm not a scentist so i don't know the technical terms, but i'll try and get around to looking up some info.
No the $170 flowtech or magna cat don't flow as well because thier cheaply built in camparison to the stock cats. WHY? well this has allot to do with the tight epa regulations put on car makers today. the most aftermarket cats are imported and arn't held to high standers. They squeak by with the min rating allowed.

jedi posted a link not to long ago for an aftermarket cat that actually dose flow better than the new GM cats, but it costs.


I got to thincking about this. Max you TA has header and an lt1 right? your still useing the stock size cat right? with headers and all the mods you have you need to go with a bigger cat.

[Maximus]

I got to thincking about this. Max you TA has header and an lt1 right? your still useing the stock size cat right? with headers and all the mods you have you need to go with a bigger cat.No mine has a LS1 and yes it does have headers.Here are some pics of the SLP loud mouth exhaust like what's on mine.All it has is that resonator for a muffler.When I got it the resonator was removed and a Dynomax bullet was used to replace the resonator.I took the bullet off and installed a Magna Flow 14' round race muffler.It's the longer one in the pic.Below are pics of all the parts that make up my exhaust from the headers back.I do agree todays cats flow extremely well.But anyway you look at it they are a restriction.If KY had inspections I would have cats on my rides or if they needed them for backpressure I would use them.But my S10 runs better with the glasspack and the TA nees the most amount of exhaust flow possible.I would say 3 out of 5 Fbody owners who build their rides for performance get rid of the cats if they can get away with it.Especialy the ones who are running true dual exhaust.The LS1 is So very choked from the factory.Anything done to a LS1 to free up the intake and exhaust even minor ones have shown significant hp/tq improvements.Again in several applications a cat is needed and performance can be hurt if removed.Not all of them but several.http://www.sicgmtrucks.com/forum/attachment.php?attachmentid=849&stc=1http://www.sicgmtrucks.com/forum/attachment.php?attachmentid=850&stc=1http://www.sicgmtrucks.com/forum/attachment.php?attachmentid=851&stc=1

[imdawrlus]

how is a non gutted, properly functionally cat NOT an expansion chamber?? you dont make it WIDER inside when you gut it out.....also, wouldent a muffler be an expansion chamber??

[bvr775]

when you gut it you pull the stuffing out therefore you can put more air in.and remeber cold air takes up more room than hot air. without the catilist the air cools quikly in the chamber. Plus the holes in the honeycomb matiriale of the new cats help the airflow straiter