Stupid question?

[Greyg]

I've talked to guys (who wish to remain anonymous) that have removed their catalytic converter and gotten huge gains in FE. I'm told this is illegal (which I figured it would be) but is easy to get away with in areas where there are no emissions tests to pass. None of the mechanics/technicians I work with are willing to do this, so I'm assuming it's very illegal. What are the pro's and cons to something like this? How big are the fines? How come I've never heard of this before? Cripes, I'm 40, I didn't think I was that uninformed.

[Jay2TheRescue]

I think if you are getting great gains from removing the cat then it was probably bad and needed to be replaced anyway. Removing it is highly illegal, even in areas that do not do emissions testing.

[theholycow]

In old (25+ years old) cars, the cat might not flow freely -- and might be rusted/worn to uselessness now anyway. Modern cats flow as well as the rest of the exhaust system.

[VetteOwner]

Originally Posted by theholycow

In old (25+ years old) cars, the cat might not flow freely -- and might be rusted/worn to uselessness now anyway. Modern cats flow as well as the rest of the exhaust system.

ya main reason wny my chevettes has gone "missing". 28 years old figured it was plugged or somehitng goin on with it...

ye sit is illegal to remove/modify any emmissions part on a car besides replacing it. but i dunno if i really gained anythign from it... sounds like a small diesel engine while idiling now...

[Backtobasics]

I agree that the people who saw improvements removed a clogged catalytic converter. The new "monolith" style are very free flow, and are minimally restrictive.

[BEEF]

I have heard the gains with a normal (unclogged) cat are about 1-2mpg and the fine if a shop takes it off is $2500 for the shop. at least it is in virginia. lived there most of my life. not sure for an individual.

my info may be dated and may have changed but I don't think it is worth it.

[mini-e]

Catalytic converters cause very little loss in power or efficiency, searching around the internet a couple times for 2-3 hours i found 1-3% power gains with removal and that was way up in the powerband. Catalytic converters work very well- if you ever get behind a car that stinks it is likely the cat(s) are removed or non functional. i was behined a 2004-6 audi a4 yesterday that stunk, it was lowered and had a custom exhaust, so the guy was running catless and pig rich for that oh so important 2% (or what ever) gain at WOT. Get off a plane in Bangkok or Mexico City and gag. Exhaust coming out of non emission controlled cars and trucks is utterly foul. I grew up in L.A. in the early 60's 70's and the air was very, very, gross. Now it pretty good, considering... Catalytic converters are in use for very good reasons.

[R.I.D.E.]

$2500 for individuals, $5000 for shops.
regards
gary

[JoeBob]

Originally Posted by mini-e

Catalytic converters cause very little loss in power or efficiency, searching around the internet a couple times for 2-3 hours i found 1-3% power gains with removal and that was way up in the powerband. Catalytic converters work very well- ... I grew up in L.A. in the early 60's 70's and the air was very, very, gross. Now it pretty good, considering... Catalytic converters are in use for very good reasons.

Same here. The air in LA is better (far from perfect, though) than it was then, even with more than double the cars on the road. And many more miles travelled per car than back then. Be nice to other people, leave the cat in place (or replace it if it is bad).

I've tried removing a perfectly good cat once upon a time in the '80s...no difference in mileage...so it went right back on.

[Ford Man]

Years ago it wasn't illegal to remove the catalytic converter yourself, but I think shops could be charged as much as $25,000. (federal fine) if caught removing them for you. Back in the '70's I had removed them from a couple of the cars that I owned so I could use leaded gas without the worry of it stopping up the catalytic converter. I don't remember it ever doing anything drastic for FE though.

After doing a search on "catalytic converter removal laws" I found out that the clean air act of 1990 is when it became illegal to remove them. It is even illegal to replace a known good converter with any other converter high flow or not.

[2000mc]

spec i've used for checking cats is 2psi @5000 rpm in park or neutral. but i've never actually tested one that was that low, because i'm only checking them because of a customer complaint where i think the problem is the cat and it is only tested to confirm the problem before dropping the big bucks ona new cat.... well my point is, could have someone test it, and see if there is excessive back pressure.

i've also heard of people getting much better mileage when thier converter is getting plugged up... not sure why that would happen, but i've heard of it.

and my last 2 cents... i think in iowa fines are $10000/shop, $1000/person for removal.

[BEEF]

it looks like that regardless of if you save gas by removing it, it still will not offset the fine if you get caught with it off of your vehicle.

[VetteOwner]

yea but for us in non inspection/annuall check of any kind, whos gonna check?

tire store didnt say a thing about missing the cat off my car (quite obvious as a straight pipe is welded/clamped in place)

and any cop that pulls me over isnt going to get down on his hands and knees to look...

[severach]

Originally Posted by VetteOwner

and any cop that pulls me over isnt going to get down on his hands and knees to look...

I am not located in an emissions check area but people report that police may visually check for a catalytic during a safety check. You probably wouldn't get caught if your straight pipe was shaped like a real catalytic.

[Mr Incredible]

My 91 Camaro had a disintigrating cat. Whack it and you could hear the pieces rattling. When I took it off I could pour out the tiny bits, and see the bigger pieces moving around. I took a long, pointy piece of rebar and broke out the entire insides.

It sounded different, but since I wasn't all into FE at the time I didn't see if there was any change in mpgs. It did sound a little better, though.

Nobody would be any the wiser of it unless they took off the cat and looked through it. Who's to know?

But with people here throwing parties with an FE gain of .5 mpg, it may be worth a try.

[theholycow]

You could also hollow the cat and shove a straight pipe through it.

I'm a member of a forum full of people who have removed their cats, and have never heard of anyone getting in trouble for it. I suspect that enforcement is nearly non-existent except for emissions inpsections.

[Jay2TheRescue]

Originally Posted by Mr Incredible

My 91 Camaro had a disintigrating cat. Whack it and you could hear the pieces rattling. When I took it off I could pour out the tiny bits, and see the bigger pieces moving around. I took a long, pointy piece of rebar and broke out the entire insides.

It sounded different, but since I wasn't all into FE at the time I didn't see if there was any change in mpgs. It did sound a little better, though.

Nobody would be any the wiser of it unless they took off the cat and looked through it. Who's to know?

But with people here throwing parties with an FE gain of .5 mpg, it may be worth a try.

I remember on my 1980 Pontiac wagon the cat was partially rusted and leaking. Being 17 at the time and not having the $400 needed to replace the cat at the time I took it to a welding shop and had the cat welded back shut for like $5.

-Jay

[dkjones96]

Originally Posted by theholycow

You could also hollow the cat and shove a straight pipe through it.

That's the best way to do it. Just hollowing out the cat means you end up with this dead space in the exhaust where the gases expand into the cat chamber and then get recompressed into the exhaust system again. Usually this is no big deal because the honeycomb in the cat keeps the air flowing in one direction and without much turbulence but without the air direction it becomes a mess in there.

[ihatemybike]

I had a 94 Astro where the honeycomb in the cat shifted and clogged the exhaust. Disconnected the tail pipe, broke it apart, and revved the engine to blow the pieces out the back. Noticed no performance loss or change in MPG.

[Mr Incredible]

One of my horsepower books mentions the theory and construction of expansion chambers for horsepower. The cats are placed in an agreeable postion for such a job. I can't remember the details, but an empty cat not modified by a straight-through pipe might be useful.

[mango]

Vehicles without cats smell horrible! Please be considerate of other people driving behind you and leave it in!

[bigrod]

Removing the cat is not worth it unless you have a turbo car. Years ago I ran a straight pipe on my turbo 240sx and saw quicker spool time and more pull at WOT. I'm sure if I didn't drive like a maniac back then I would've increased FE.

A diesel friend of mine owns a Dodge Ram Cummins turbo diesel and a couple VW TDI's and he reported significant mpg and power gains from removing the cats. Can't remember the actual numbers.

In the end its not worth it in a naturally aspirated car.

[aalb1]

Originally Posted by bigrod

Removing the cat is not worth it unless you have a turbo car. Years ago I ran a straight pipe on my turbo 240sx and saw quicker spool time and more pull at WOT. I'm sure if I didn't drive like a maniac back then I would've increased FE.

In the end its not worth it in a naturally aspirated car.

And keep in mind that boosted cars need to run richer in boost to keep detonation out of the picture. The richer A/F ratio will quickly clog the honeycomb of the cat as well. Typically when boosting a car, if you don't mind richening up the fuel map for boost, then why is FE even on the radar? If you have the ability to alter your fuel map you should be looking to lean it out a little more knowing that you're going to be lighter on the throttle than what your car manufacturer's design team expected.

IMHO fuel economy and low emissions should run hand in hand.