silvervette05

I've been told there is little to no HP gain from removing your cats, i'd like to know if anyone has actually dynoed there car before and after the removal..If so what were the gains..I am still running the cats on my Z06 setup,and i am thinking of removing them..Thanks guys..

Jonathan..

8850

With my 08 C6 and Z06 manifold/cats I went from 409 hp w/cats to 427 gutted but also with an underdrive pulley at the same time. Don't know which gave what.

LeMans05C6

bump... im curious about this as well. I live in Texas and am leaning towards the LG Super Pros w/ cats to pass emissions but would like to know what i will lose by having them.

wbear

The cats you are considering are just as illegal as no cats at all under Federal law. You cannot move, change or tamper with the position of the factory cats. As soon as the headers go on you have become illegal whether or not you add the cats. All they have to do is raise the hood and look to see you are a violator. Save yourself the $400 and the hassle of running the rear 02 sensor wires. Most believe no cats save around 5 hp.

LS1LT1

True, although in the event of an emissions spot inspection (rare but it does happen) it's likely still a little better to be able to point out that one has a set of those tiny, high flow cats under there versus nothing at all.

LeMans05C6

Okay so here is my question. I know i can't be the only one who considers getting headers on my car. And I am sure many people have done them as well, how do they pass emissions or is there something I am missing.

LEAVINU

..... never fails in the catless threads. Someone always has to come in and talk about the emissions laws. Live alittle sheesh!

I enjoy my ported heads mild cammed catless aftermarket header Corvette. :o

LEAVINU

I've passed emissions in 2 different vettes with headers and no cats. That was the legal way of driving to the emissions stand and getting in line in case anyone wonders. GA does not do visual inspections like some other states do.

No gimmicks or tuning tricks.


Now......... H/C setup that takes alittle bit more know how to pass emissions. :o

LS1LT1

This is turning into a discussion that is best kept off of a public forum where anyone can read it.

P J

well i'm new to the forum and i was wondering when removing cats, will it have a bad gas smell? the reason for asking, because tsp has headers i was interested in with a 3 inch x pipe no cats.

Evilways

Just some info, during a dyno test with and without cats on a new camaro w/ long tube headers, the camaro made more hp + tq with cats on than without. I think the difference was +4 HP and +7 rwtq with the cats, but it's been a few weeks since I saw that, so may be off by a number or two, but it definately made more WITH cats. And, you don't have to worry with the bad smell .

silvervette05

Well,maybe i should just keep them on for now..If i decide to go to Lt's later on down the Road i still think i will go catless..

Jimmy Z

mittens

cats come off of everything i own. haha

then when i did the headers on the vettte i thought OK I WILL DO THE NICE SET UP.

ordered the $$ headers with hi flow cats. 2 months later, i put the off road X pipe on (casue they messed up and shipped me both)...been cat less since then on the vette too.

wbear

Yes. I recomend leaving the cats alone until you put the headers on then go for an offroad set up with out the cats. Its not worth the 5 hp you would gain because you will have to:
1. Have some kind of pipes custom made to replace the cats.
2. Get a tune just to turn off the check engine codes that will show up when the cats/rear O2 sensors are gone.

wbear

I have the headers and off road set up with no cats and love it. The approx 30 hp increase is enough to give a seat of the pants boost you can feel and the sound has more muscle car to it.

My opinion is the people are doing one or more of the following if they have headers on their car:

1. Lucky enough to live in a state that does NO checks (that's me).
2. Lucky enough to live in a state that does NO visual inspection but just plugs in a scan tool to check for codes/history which they have removed with a tune etc.
3. Got thru the check by paying someone off or some other scam etc.

Maybe someone else can add something to this list.

See what La. has for their checks. maybe you will get lucky.

wbear

Hold your horses. I only mentioned the law because it is very relevant to his decision on running cats with his headers. I don't think he realized that cats with his headers will not make the car legal.

ANY modification the the to the engine or any system related to it that could effect emissions is more than likely a federal violation. This would include tunes, headers, different injectors, heads, cams, manifolds etc etc. Even installing a cold air intake or a automatic transmission tune would be a violation according to the letter of the law.

Luckily for us most of the 50 states don't want to catch violators or they would have the state police run random roadside stops with a visual inspection followed by an examination of the exhaust gas coming out of your tail pipe to make sure it meets the specs for your year of vehicle. That would kill the aftermarket powertrain accessory industry and us hot rodders.

I am not a tree hugger, I am a violator just like you and half of the other people on this forum. Here is more of my opinion on headers:

"No smell to bother me on my 07. Smells no worse than any pre cat car, i.e. 1974 and older.

Advantages you will get over cats: less tunnel heat, better sound, better flow (the 5 or 6 hp), save $300 to $400 on the cats/rear O2 extensions plus you don't have the hassle of routing the rear O2 wiring. I have no drone with headers, no cats and the stock exhaust.

I recommend going catless if you want the above advantages. You can always add cats later if you change your mind. As far as violating the federal emissions law, once you install the headers the law is broken cats or no cats."

How much hp gained depends on the application but the fact of better flow without is indisputable IMO.
As far as the smell it seems to be about 50/50 on here. Of course there will be some odor behind the car, its a large engine burning gasoline for Christ sake. DON'T STAND BEHIND THE CAR WHILE ITS RUNNING! I didn't do it in the 60's and I don't do it now. Use exhaust hoses if you run it indoors. Even with cats you are in danger of inhaling carbon monoxide. An uncountable number of people drove vehicles from the early 1900's till 1975 when cats were forced on the industry. No one talked about smell. They drove the cars and enjoyed them. Keep the engine shut off if you are not driving it or use the precautions mechanics do if you are working on it. Remember CO is odorless, colorless and tasteless.

In the end its a personal choice a person will have to make. I am very satisfied with my off road pipe.

FU

You should gain @ 5 h/p from removing the cat's. My opinion (FWIW) is to leave them on.5 h/p can be made up very easily , in so many different ways.
BUT
If you decide to pull the cat's , with out a doubt get the car tuned. The tuner will clean up the exhaust and the car will no stink as much.

Sulley

I believe you can (change) the cats when they are damaged or the car is 4 years old or has 50000 miles. Hard to prove they were not damaged when they are long gone.

Rkreigh

hp gain is largely dependent on how much HP the engine is making. if the factory cats flow enough to keep up with the engine, the hp gain is relatively small (+5) when you step up to a much higher flowing set of heads, cam, FI, ect.... the cats "cost" a bit more hp

on a relatively stock car, not worth the hassle IMHO. if you have a maxed out stroker or a big boost FI car, different story

hope that helps