Trying to get a feel for the level of difficulty on gutting out the cats on my '04 6m coupe.

1. Is the hp gain worth the hassle?
2. How to do it?

I did a search on this site and don't see any references to it.

 

I would leave the main cats alone and just gut the pre-cats:

http://mikemercury.home.att.net/precats.htm

 

..Except he shouldn't have pre-cats on an '04.

If you gut the main cats you'll have to run O2 sims / edit the codes out w/ HP Tuner / LS1 Edit package. Personally, I think it's socially irresponsible to drive a street car w/o cats. There just isn’t much to gain but plenty to loose.

 

you can gut them and not run o2 sims as long as the engine is fairly tight and clean running- which it should be. And there is some hp to gain. Whats wrong with not running cats?? Here in northern colorado is see 50+ beat up farm trucks on the roads every day. There is no way our cars put out any where near that level of pollunts even with out cats.

 

My 2004 CE Coupe has precats as in the picture, although, I don't know if they have any material in them. Just put an x-pipe on this weekend and I was a little suprised to see them. Perhaps some leftover parts at Bowling Green?

 

I would wager that a large percentage of the cars on this forum run on the streets without cats.

 

Great link Mike. A pic is worth 1,000 words.

As far as being responsible:
The LS1 is a very efficient motor that has far fewer hydrocarbons in the unspent fuel that is delivered via the exhaust.
Diesel, in recent studies, is a far worse pollutant than originally thought. They are also having setbacks in the world of hybrid vehicles from a recent article I read in MotorTrend?
Given the type of gas mileage these cars get in ratio to the number of cylinders, I'd bet there are many cars on the road today, not to mention commercial vehicles, that are far worse than our Vettes without cats.
Heck, I like a good debate anyway.
Thanks for the help gents. Cats are going next week after picnic with Connecticut chapter tomorrow.
Head and cam coming from Cartek in Aug.

 

first time I've ever heard that.

Source or link ???

 

oh... P-L-E-A-S-E

save it for the environ-mentalcases.

 

Absolutely *not* worth it in my opinion. Figure a 5 hp gain over an after market cat-back.

Mark

 

That's my only snag now is cash flow for some of these systems.
Some of these cat-backs/headers are ridiculously pricey.
HP is an expensive game, but $1500-2000 for an exhaust system?! :shocked:

The low buck/cat mod is looking pretty tasty so far.

 

Except it's not as low buck as you think. Consider:

Find a lift, drop the mid pipes, gut the cats. DIY or labor of 3 hours

Buy O2 sims, install, $60 plus 1 hour labor
OR buy LS1 Edit, $100 plus for a license or a shop can do it for you, figure $400 plus.

What is that gonna get you? We did this with a spare mid pipe, dyno'd before and after (same day, temp, etc.) It was worth 6 lousy horsepower
Now you're driving a vehicle that can't pass smog, pollutes more, will be harder to sell or worth less, its a FEDERAL CRIME, and for what? 6 horsepower. Gimme a break. The argument "Other vehicles are polluting even more." is foolish. Why make things worse? Especially for such a small gain.

The enviro ***** are all over car enthusiasts as it is. Don't give them another reason to hammer performance cars and owners when it's not worth it.

 

Cartek is doing the LS1 edit for me and I have a friend with full hydraulic lift in his garage so those are not a problem at all.
The labor is the fun part. I spent 20 yrs rebuilding engines, bodywork and tinkering with cars. The little time I get to goof around now is kinda fun for me anyhow.
In terms of the "Federal Crime". I don't intend to drive around polluting the air. I plan on getting high flow cats for her by the Fall.
The argument about other vehicles polluting worse is very valid when compared to emissions from the LS1. I will do a before and after emission comparison if I can in the next few weeks and post the results.
I'd bet a lot of beer and pizza that the difference is VERY small.
Besides, gutting a pre-cat is not removing the cats all together anyhow.
I'm still running through the factory cats.
In addition to your 6 hp claim:
I've had 2 shops that do a lot of work for forum members tell me they see up to 15 hp gains from removing cats. More gain for H/C cars of course. 6 on a bone stocker might be about right, but I'm not staying bone stock for long.
Check out the emissions #'s on the LS1 compared to a Honda Civic.
http://www.epa.gov/autoemissions/select.htm
We have the same air pollution score assigned by the government agencies AND with TWICE the number of cylinders and nearly 3X's the HP. Hmmmmmmmmm

 

Once again, Tim is correct. I see those pup cats on my '04 everytime it is on the lift...

 

The shop up the road did mine a an hour. With a chisel, hammer, long screwdriver, and a shop vac. Just make sure to keep the pre cats lower than the cats to prevent debris passage to cats. Seems to breath a little better. Shop charged me $45. Pretty good deal. Good luck.

 

Simpleman: In your first post you didn't say pup cats, or pups only. If that's what you're talking about, not the mains, then it won't hurt much or cost much. Of course, it won't gain much either

As far as no cats being worth 15 hp...

Having access to a chassis dyno is neat, you can test out these claims. We dyno'd my heads/cam car, open headers then full exhaust (stock cats, x pipe, and Corsa cat back). The difference was 12 HP. Not all the loss is from the cats, so if I were you I wouldn't expect any 15 hp from removing the cats.

 

Ahhhhhhhh... Good to know. I read a couple threads from folks telling us they got 10-15 hp gains by removing cats only.
Well, I'll be in Carlisle looking to get the exhaust done.
Considering Kooks headers and Borla Stingers. I've heard the Stingers and like the tone.

You also may have gained less horses via cat removal with different H/C combo than stock. I've seen alot of seemingly conflicting hp gains due to combination of mods. Just a though.

 

"your results may vary" is true. Going from 4 cats to none Vs. my 2 cats to none will change things, as will a wilder H/C combination. That being said, I think for a stock cube motor my results will be pretty representative.

 

I added an x-pipe in place of the stock main cats on my 99'. There where no pup cats in 99 and got 10hp at the wheels across the board. So the bang for buck is there but no on has mentioned one important thing. The smell! The exhaust will burn your eyes at a stop light with the top or windows down if the wind blows right. It was not worth it to me in retrospect.

 

I could do without the stink. I have a 73 Olds Omega for that.
Revised plan.......
1. gut pre-cats only
2. buy Kooks/Stingers at Carlisle
3. figure out whether I want H/C on this car OR
4. hold out for next Summer's Z06 which should have :shocked: performance.
Thanks all for the input.