remove cats?

[energumeno]

I read that somebody removing the cats from his car as part of the exhaust upgrade.

Does somebody know what would be the advantages of removing them?

[formerice]

I would'nt do it, O2 sensors will be f'ed up. Rather check out the Hiflow cats from Dynatec or others. They have almost no restriction and the motor will run right. Some including me have had check engine lights with those, but the cars still run good. Also you don't want to cause air pollution. Headers, hiflow cats, and a good cat back exaust will give much better performance, plus sound better.

[NYC_SRT8]

I read that somebody removing the cats from his car as part of the exhaust upgrade.

Does somebody know what would be the advantages of removing them?

I removed my cats( actually gutted them) but I also have longtube headers and cat-back exhaust. I would say 5-10hp gain and a way louder exhaust note. I through codes speracticly...anywhere from 40 to 1000 mile inbetween clearing them. The only downside is you smell the exhaust fumes very strongly inside the car with the windows down. Other than that I love it.

[MikeEast]

Today's cats have virtually no airflow restriction at all. The restriction on 5.7's comes from the swivel joint which necks down do around 1.75" or so. That's the main benefit from high-flow cats, removing that joint, and a slightly different cat core design.

Almost all the cat cores are made by a very small number of companies - not naming names, but almost all cats for one large company were designed and are manufactured using VAX'n that I used to maintain. There is negligible restriction...

Removing them only opens up all kinds of emissions related problems, from having to replace them when you have to do smog checks (sooner or later it will happen) and throwing annoying codes.

I removed my cats( actually gutted them) but I also have longtube headers and cat-back exhaust. I would say 5-10hp gain and a way louder exhaust note. I through codes speracticly...anywhere from 40 to 1000 mile inbetween clearing them. The only downside is you smell the exhaust fumes very strongly inside the car with the windows down. Other than that I love it.

Keywords there - "I would say'. I would say 'show me'. Dyno before and after please...

Mike

[NYC_SRT8]

Today's cats have virtually no airflow restriction at all. The restriction on 5.7's comes from the swivel joint which necks down do around 1.75" or so. That's the main benefit from high-flow cats, removing that joint, and a slightly different cat core design.

Almost all the cat cores are made by a very small number of companies - not naming names, but almost all cats for one large company were designed and are manufactured using VAX'n that I used to maintain. There is negligible restriction...

Removing them only opens up all kinds of emissions related problems, from having to replace them when you have to do smog checks (sooner or later it will happen) and throwing annoying codes.

Keywords there - "I would say'. I would say 'show me'. Dyno before and after please...

Mike

I have something better than a dyno sheet....TRACK RESULTS...12.75 with cats and 12.71 without in worst DA. That was the only thing changed inbetween those runs too.

Oh yeah, your statement about there being near to no flow restriction is far from the thuth. If you compare stock cats with aftermarket highflows the flow rates are waaaaaaay better on highflows reason being there is less material per square inch. So there is less restriction for the airflow. So it's physically impossible for a stock cat with almost 600 cell count to flow as good as a aftermarket high flow with a 200 cell count. Then there is the extreme...NO CATS...has so much flow that you loose back pressure. Why do you loose back pressure? hmmm. Because there is a dragstick change in flow restriction, actually no restriction from there being no cats!!!!!!!

ANNNNNDDD, the codes will be a thing of the past after diablo releases the tuner...it will have the ability to delete the rear o2 sensors.

[done]

I have something better than a dyno sheet....TRACK RESULTS...12.75 with cats and 12.71 without in worst DA. That was the only thing changed inbetween those runs too.

Ohmigod, 4 hundreths of a second inprovement!!

I would think that there could be any number of explanations for .04 seconds.

[NYC_SRT8]

Ohmigod, 4 hundreths of a second inprovement!!

I would think that there could be any number of explanations for .04 seconds.

Yeah, however the DA was worst by a few hundred feet and the 60ft was withing a 100th of each other (1.91 to 1.92). Now I didn't say you can get 100hp from deleting the cats, I said between 5 and 10hp.

[Super T]

5 horsepower sounds believable, 10 might be pushing it. Even if it was 20, I'm not willing to
1) Spew even more s*** into the air... I already burn gas like crazy
2) Risk failing emissions/inspection when that time comes
3) Have to F around trying to shut the car up complaining about it

High-flows will get you, for all practical purposes, to the same level as a delete. I'd go that route.

[MikeEast]

I'll stand behind my comments - teeny little gains like that aren't worth the trouble and expense. I'd bet that in the future somewhere, that will end up costing a whole lot more money that you thought. You will have to pass emissions in New York at some point, unless you 'know a guy', and they are (or were when I lived in the Greater Syracuse Pollution Zone) cracking down relentlessly on Inspection Stations that handed out stickers without testing.

What's the fine in NY these days (not that this applies to the car owner, yet) for screwing with emissions related equipment? I'm pretty sure it's in the 5 digit range.

Of course it's up to the individual car owner whether or not to go the cat-delete route, but I personally think it's bad advice to say it's a good thing. 4 whole hundredths? No thanks...

Mike

[NYC_SRT8]

My arguement was never that 4 tenths are worth gutting your cats. You quoted me and said prove that you can show a 5-10hp gain. However, my argument was that you do see a gain eventhough mininal, it's a gain. Is it worth it? thats a individual choice.

My other argument was that stock cats do not flow as good as aftermarket or no cats at all. Like I stated before it's physically impossible for something using the same material covering more surfice area to flow as good as the same material covering less or no material being used at all. I'll stand behind my comments as well with facts.

[MikeEast]

I never disagreed that high-flow cats aren't a good idea, I put them first one the list of mods to do, about tied with an AirHammer and a flashpaq as the best bang-for-the-buck.

I did disagree with gutting them entirely...

It's all good though...

Mike

[JMatt]

On a stock SRT-8, with headers and high flow cats and a cat-back exhaust system, deleting the cats gives an 8HP improvement over high-flow cats. Yes - I have the dynos to prove it.

[NYC_SRT8]

I never disagreed that high-flow cats aren't a good idea, I put them first one the list of mods to do, about tied with an AirHammer and a flashpaq as the best bang-for-the-buck.

I did disagree with gutting them entirely...

It's all good though...

Mike

Your entitled to your own opinion...yes buddy it's all good...

[NYC_SRT8]

On a stock SRT-8, with headers and high flow cats and a cat-back exhaust system, deleting the cats gives an 8HP improvement over high-flow cats. Yes - I have the dynos to prove it.

So my guess-timent was pretty accurate... JMATT again to the rescue...

[JMatt]

And here's the runs:

I cut off the lower half of the graph in order to show this range better. You can see the cat delete makes no difference until higher RPMs - which is exactly what you'd expect. With hears and cat-back, the exhaust system - including the cats - isn't the restrictive point until higher rpms.

Runs were done back-to-back. Same facility, same temp, same conditions, same dyno, same operator.....you get the picture.