Thread: choppin out catalytic converter

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  1. #21 Re: choppin out catalytic converter 
    SE Level Member brodyman's Avatar
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    Do you run at Bandimere at all riceburner?
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  2. #22 Re: choppin out catalytic converter 
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    Hey i did chop my cat to and i welded straight pipe in place. The good news on my end the o2 sensor is not smack dab on the convertor. So with that said i left mine plugged in while welding and i've been driving if for almost 5 months and not one sign of the check engine light and know it works.

    Bad news is according to my Info Center ive lost 5 or so MPG. and little over 100 miles to the tank. Now could this be caused from something else not sure. But I think the car is running to lean.

    But let us know
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  3. #23 Re: choppin out catalytic converter 
    GT Level Member njbrain's Avatar
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    Very often you will loose gas mileage when you cut out the cat.
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  4. #24 Re: choppin out catalytic converter 
    GXP Level Member Iron Indian's Avatar
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    If you lost MPG you have other problems. Getting rid of a cat WON'T kill gas mileage period, if anything it'll help it anyway. I've removed cats off of 3 cars so far I never lost any mileage, if anything I gained. Thats not true at all.
    Shawn W. Larsen

    2005 Pontiac GTO 6.0 LS2/A4... Stalled/Cam Only: 406 RWHP , 370 RWTQ

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  5. #25 Re: choppin out catalytic converter 
    I live here. UR LOSN's Avatar
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    I lost 1mpg.........
    2001 GTP- PT76 turbo, Intense Drag cars old engine, Stage 4 Intense turbo cam,FMIC,150 wet,Double roller timing chain,Diamond forged coated pistons 8:0:1,Diamond piston rings,Cryoed L32 connecting rods,Cryoed crank,Clevite77 main bearings,Clevite77 cam bearings,Clevite77 L32 rod bearings,ARP Everything, Intense/meizere true billet Flexplate,Intense Wilson UIM/LIM,Intense oil pressure kit,Cometic,OE-R lifters,Cryoed L67 block,ATI turbo dampner,80# inject,Weldon 2035 fp,Aero Fuel Rails,AL cradle
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  6. #26 Re: choppin out catalytic converter 
    GT Level Member njbrain's Avatar
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    Quote Originally Posted by Iron Indian View Post
    If you lost MPG you have other problems. Getting rid of a cat WON'T kill gas mileage period, if anything it'll help it anyway. I've removed cats off of 3 cars so far I never lost any mileage, if anything I gained. Thats not true at all.
    It all depends. Every engine is engineered to have a certain amount of back pressure. If you drop it to far, you will not only lose torque, but also horsepower. When I put a cat back in my car, I gained about 2mpg city, hwy stayed the same.
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  7. #27 Re: choppin out catalytic converter 
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    Well i have chopped plenty in my day to. lol. my dual setup on my old camaro and it runs better than ever. But i'm not sure why ive lost so much, as a matter of fact i was talking to the wife and our van (00 pontiac montana 3.4) She told me she's been running out of gas alot faster to. We use to be able to get 390miles on one tank now shes getting less than 250. Could i just have a string of bad luck im not sure. But no check engine lights or abnormal driving, and no i didnt cut her cat off lol..
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  8. #28 Re: choppin out catalytic converter 
    GXP Level Member Iron Indian's Avatar
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    I'll I know is my Black GTP when it had just a CAI and a 3" Off Road DP and actully gained a couple MPG. With a good tune, colder plugs. ILGPC IC, 3.25" it gained a little more. I'd have to figure it up but it gained a good 3-5 MPG than stock.

    My car with its mods and 3.29s + 3000 stall still gets better MPG than it did bone stock with over 100,000 less miles...
    Shawn W. Larsen

    2005 Pontiac GTO 6.0 LS2/A4... Stalled/Cam Only: 406 RWHP , 370 RWTQ

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  9. #29 Re: choppin out catalytic converter 
    The Blue One blueguy's Avatar
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    Meh...my cam hurts MPG

    But when I had my 3" Exhaust custom made and my 3" Shorty DP put on (No cat, res., or u-bend) I gained about 4 mpg's...but staying out of it was the problem
    Sold WBody's: '03 Blue GTP/'98 Green GTP/'98 Silver GT/'05 GXP
    '99 Chevrolet Silverado Classic Z71 4x4 - K&N Intake/Gibson Exhaust #TRUCKTHINGS
    '12 Buick Regal Turbo - ZZP CAI/20% Tint/HID's
    '89 Ford Mustang LX Notchback - LM7 5.3, 4L80, 9", HX40
    '04 Chevrolet Corvette MRM A4/LS1 - TSP LT's, 3"O/R X, AFE S2 CAI
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  10. #30 Re: choppin out catalytic converter 
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    I'll admit I had my foot in it for the first week and its not that much to brag about now. But could it just be the winter fuel, im not sure if thats even true but my friend said in the winter his toyota gets horrible mileage. Honestly its getting on my nerves now, knowing i was getting 26 mostly on my GT and now close to 15- 22.
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  11. #31 Re: choppin out catalytic converter 
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    try this link from regalgs, some good info, http://www.regalgs.org/forum/viewtop...ilit=catalytic

    the previous owner of my car decided to order a dp without a cat but had the second o2 turned off in the pcm. As far as mileage goes, if i keep my foot out of it I can get 26-30mpg depending on conditions.

    With your current mods how much boost do you have? Until you find the cat to be a serious enough restriction to be removed,gutted, etc just leave it on.

    I have seen sparkplug defoulers used on a 3100 monte carlo. Supposedly it works but the guy also took his cat off for power(because his high mileage 3100 needed it?) and had not changed his dexcool in 5 years...yikes. I believe he blew a head gasket on his trip from stl to las vegas.

    on a side note: Tests in car craft magazine have shown high flows used on 500 horse engines to only restrict at a most 10 hp. Same as glasspacks used as resonators, maybe a 2 hp loss.
    Last edited by Golgo13; 10-27-2008 at 07:05 PM. Reason: organization or lack of
    2002 GTP
    custom HOK paint
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  12. #32 Re: choppin out catalytic converter 
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    Well after chopping the cat almost 2 months ago and the mileage going down about 2 weeks ago. The Engine light finally came on today throwing off the o2 code. so i guess im going to have to order the O2 eliminater anyways. Any ideas or suggestions on that. should i get an eliminater to plug or is there a way to by pass...
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  13. #33 Re: choppin out catalytic converter 
    SE Level Member brodyman's Avatar
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    Go to 3800performance.com. They have the kind you plug right in
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  14. #34 Re: choppin out catalytic converter 
    The Blue One blueguy's Avatar
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    Quote Originally Posted by Golgo13 View Post
    With your current mods how much boost do you have?

    GT Grand Prix
    Sold WBody's: '03 Blue GTP/'98 Green GTP/'98 Silver GT/'05 GXP
    '99 Chevrolet Silverado Classic Z71 4x4 - K&N Intake/Gibson Exhaust #TRUCKTHINGS
    '12 Buick Regal Turbo - ZZP CAI/20% Tint/HID's
    '89 Ford Mustang LX Notchback - LM7 5.3, 4L80, 9", HX40
    '04 Chevrolet Corvette MRM A4/LS1 - TSP LT's, 3"O/R X, AFE S2 CAI
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  15. #35 Re: choppin out catalytic converter 
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    4th post
    as of now i have 3.25 pulley,thrasher cai,2.5 catback with u bend delete flowmaster plugs 2 levels colder and 160 thermo... with a good set of headers , downpipe and cuttin cat out the mix any ball park figure of hp gain?
    2002 GTP
    custom HOK paint
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  16. #36 Re: choppin out catalytic converter 
    GT Level Member riceburner's Avatar
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    brodyman, i do run at bandi when i can. only got the girl up once this season. Im hoping to have both the bird and gtp up next season though.
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  17. #37 Re: choppin out catalytic converter 
    The Blue One blueguy's Avatar
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    Quote Originally Posted by 98GT3800 View Post
    Well after chopping the cat almost 2 months ago and the mileage going down about 2 weeks ago. The Engine light finally came on today throwing off the o2 code. so i guess im going to have to order the O2 eliminater anyways. Any ideas or suggestions on that. should i get an eliminater to plug or is there a way to by pass...
    ZZ Performance sells them also. I had one for sale until I actually got off my ass to put it in
    Sold WBody's: '03 Blue GTP/'98 Green GTP/'98 Silver GT/'05 GXP
    '99 Chevrolet Silverado Classic Z71 4x4 - K&N Intake/Gibson Exhaust #TRUCKTHINGS
    '12 Buick Regal Turbo - ZZP CAI/20% Tint/HID's
    '89 Ford Mustang LX Notchback - LM7 5.3, 4L80, 9", HX40
    '04 Chevrolet Corvette MRM A4/LS1 - TSP LT's, 3"O/R X, AFE S2 CAI
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  18. #38 Re: choppin out catalytic converter 
    SE Level Member brodyman's Avatar
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    riceburner, I plan on runnin the gtp more next year. I need to update the chassis on the Super Gas car along with a whole list of upgrades. Needless to say I dont have the money for it all!!!
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  19. #39 Re: choppin out catalytic converter 
    I AM PEWPIN! rynoman03's Avatar
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    Quote Originally Posted by bluegtp91 View Post
    Meh...my cam hurts MPG

    But when I had my 3" Exhaust custom made and my 3" Shorty DP put on (No cat, res., or u-bend) I gained about 4 mpg's...but staying out of it was the problem
    I hear that. I get 29 to 31 if I don't romp on it at all. But I just can't do it. I was getting 30 the other day and some ass in a Lexus cut me off while talking on his phone. Plus it doesn't help that I have road rage . I watched my mpg go from 30 to 26 in about 15 second.

    Back to the Catt conversation I went cat less about a month ago and no my car is loud as hell in the cab at certain rpm's. Definitely going to have to get a res or a larger glass pack for resonance.
    1999 GTPHP Tuned, Ported SC/TB, 42#'s, SSAC's, ZZP Modded 1.9's/LS6 Springs/Manley's, TransGo Shift Kit, Poly Uppers, KYB GR2's/Springtech's. - 231k and traded it in. - Gone
    2000 GTP: XP, P&P'd Heads, N*\Lq4 MAF, GenV, 42#'s, PRJ Rails\FPR, Racetronix, TEP w/ 3.29 Gears, 300m, 7/8" chain, SSAC's. - Collecting dust in my garage.
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  20. #40 Re: choppin out catalytic converter 
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    i went with headers a 8 inch flex pipe and a high flow cat,the rest is stock past the cat,the gov. caught up with casper elect. and those 0-2 sims and fined them preety hard,they found mine while testing for emis. and luckaly the guy was nice and let me go,if you need an 0-2 sim i have mine
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