Gas mileage increase without catalytic converter

Gas mileage increase without catalytic converter

Postby Amnesia Wes [OP] » May 19th 2011, 1:22am

Does anyone know how much difference there is in gas mileage, when a catalytic converter is removed completely from an exhaust system?
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Re: Gas mileage increase without catalytic converter

Postby AstroWill » May 20th 2011, 2:42pm

I'm sure that it would make a 'slight' difference, but probably not enough to notice.
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Re: Gas mileage increase without catalytic converter

Postby throrope » May 20th 2011, 5:28pm

Not enough to pay the fines if sharp dressed individuals with badges and little humor find out.
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Re: Gas mileage increase without catalytic converter

Postby Mr_Bowtie » May 20th 2011, 6:45pm

Only time your mileage will increase enough to notice it is when the CAT is plugged and choking the motor. It might help slightly with acceleration.
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Re: Gas mileage increase without catalytic converter

Postby AstroWill » May 20th 2011, 7:16pm

Mr_Bowtie wrote:'93 Astro 2WD w/253K! & a "dent"($100 VAN!) SOLD

Did you run it just over 250K miles just so you could be part of the club?
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Re: Gas mileage increase without catalytic converter

Postby Mr_Bowtie » May 20th 2011, 9:20pm

I got it with 251K on it off a co-worker & she served me well for 6 months. Going to run my '96 over 250K if I have anything to say about it. :D
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Re: Gas mileage increase without catalytic converter

Postby AstroWill » May 25th 2011, 7:43pm

Mr_Bowtie wrote:I got it with 251K on it off a co-worker & she served me well for 6 months. Going to run my '96 over 250K if I have anything to say about it. :D


I've got 100k more to go on my 99, and 140k to go on the 90 Tiger GT.
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Re: Gas mileage increase without catalytic converter

Postby cowboydan » May 27th 2011, 12:04am

no complaints about my gas milage, i run a custom single exaust with a magnaflow cat.
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Re: Gas mileage increase without catalytic converter

Postby 97Safari » August 17th 2011, 3:10am

cowboydan wrote:no complaints about my gas milage, i run a custom single exaust with a magnaflow cat.


Hey Dan, how's that Magnaflow cat holding up for you? Is it a direct fit with the Y pipes or a universal fit? Did you diy or have it installed?

The reason I'm asking is it's time for my factory cat to be replaced (rattling) and the Magnaflow universal fit is the cheapest one offered at Advance Auto Parts, but it also only has a 90 day warranty.
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Re: Gas mileage increase without catalytic converter

Postby cowboydan » August 17th 2011, 5:06am

lol. what ever the shop says, don't believe them. i had 2 shops tell me i had to pay 450 for the cat, because of the whole y thing (it's not an f150 y pipe). the magnaflow and dynomax are comperable and they are both universal cats. there is enough pipe after the y to weld a couple cats on. i don't mess with exaust, i went to carline. 440 for catback incl 3" pipe, gaskets, dynomax ultra flow muffler and a kikn stainless tip (i have pics somewhere), 90 for the cat, 95 install. i have only had the cat in since winter sometime. i like it. i would weld the cat in. i am happy with the cat. but it does stink sometimes. they all do. even my wifes car stinks sometimes. did you watch my video? mine was like a penut in a jar...lol. i was only getting 15mpg or less when i bought the van. then 26mpg after my tune up. after replacing the cat, i'm now just over 29mpg. it's all highway. wifes car gets 36mpg. but she has a car. i have heard of the universal cats not lasting as long as a factory cat, but a good running engine will insure the cats life is long, that's what fudges cats up most times.... poor fire
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Re: Gas mileage increase without catalytic converter

Postby Amnesia Wes [OP] » August 17th 2011, 11:35am

The reason why I asked if removing the cat would help help gas mileage is because where I live, we are able to remove them as they are not required to pass any type of emission control in order to license our vehicles. What I'm wondering is if the cost of removal and installation of a straight pipe (somewhere around $90) would be worth the extra gas mileage. Anyone care to make a comment on whether it's worth it?
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Re: Gas mileage increase without catalytic converter

Postby chevymaherchevymaher is online! » August 17th 2011, 1:45pm

Amnesia Wes wrote:The reason why I asked if removing the cat would help help gas mileage is because where I live, we are able to remove them as they are not required to pass any type of emission control in order to license our vehicles. What I'm wondering is if the cost of removal and installation of a straight pipe (somewhere around $90) would be worth the extra gas mileage. Anyone care to make a comment on whether it's worth it?

I am a big supporter of removing them but.Unless you spend hundreds to change computer settings really you wont gain much,A little but not much.I used to do this to the V-8s the real deal is tuning where the benefits are when combined with the Reduced back pressure.More power and better mileage.I got better mileage and faster drag strip times.No other changes to the motor.Yes a carb and a Hei distributor did better than factory settings.Now that was because of a better timing curve and fuel curve combined with reduced back pressure.Now the environmentalist and computer supporters will show that in proper tune a computer will do better than that.By bombarding you with literature from every known source.Which also is true.But for absolutely free old junk parts I did better than the factory tune.Just wanted you to know it is possible, I have done it.I have written no papers being published in scientific journals,Or spent thousands documenting what I have done.So it just one mans word who does this alot.It works for me.Now the bullies nay sayers and self righteous will call me an out and out lier.And I will not participate in the childish baloney like the other night.This is my last post on this thread.It has been done,try it quietly and be happy.
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Re: Gas mileage increase without catalytic converter

Postby Phantom » August 17th 2011, 2:45pm

This is one of those very vague and over generalized questions ,
There is really no one size fits all answers so to speak of , as it depends on year make model design , if it factory cat or aftermarket cat , how good of condition is the cat in , is it like new or partially clogged up or more than partially clogged ,
for the most part you won't see anything much different unless the cat is plugged up , and if you remove it , you will cause signals to be sent to the computer that cause it to cause fuel mixture to be changed to either richer or leaner , There are ways to do it and run without , but for the street you won't see enough of a difference that justify what you have to do , The older 80's cars had relatively little computer stuff on them ,the newer car year you go the more complex the computer system is and most of today's systems can be tuned in a way that you can get better mpg with the cat installed That does not mean the cat gives any increase , it just that the systems can now be tuned in a better way in modern cars.
Cats in today's world are not as restrictive as they were in years gone by , , There are muscle cars today even in 2011;. 2012 that the cars off the showroom floor can get 11-12 second 1/4 mile times at the the track , there are cars today that have a 6 cylinder engine that get close to 34 mpg , with cat installed , You can tune engine computer system with cat off it may run better , but that does not mean better mpg ,
One person may pull it off and say they see no difference , another may say their mpg went down , another may say their power and mpg went up ( because it was clogged up and now engine can breathe) I depends on what drivetrain , what year , and what condition the parts are in , getting better mpg is about making the entire car as efficient running as possible , many things affect mpg,
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Re: Gas mileage increase without catalytic converter

Postby chevymaherchevymaher is online! » August 17th 2011, 2:55pm

Yes as usual Phantom is correct.I was dealing with older models where cats were extremely restrictive.In the era where they developed high flow cats which in and of themselves were advertised to increase milage.
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Re: Gas mileage increase without catalytic converter

Postby Amnesia Wes [OP] » August 17th 2011, 11:03pm

For what it's worth, I have a '97 Astro with the 4.3 Vortec V6, with a completely stock exhaust system with the original cat, and it has 120K mi. on it. I understand how only a clogged cat would benefit from it's removal. Is there a way to check if the cat is clogged or not? Once again, thank you all for your input.
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Re: Gas mileage increase without catalytic converter

Postby Phantom » August 17th 2011, 11:18pm

Any skilled muffler shop should be able to run a test on it , usually for free , that way if it bad they can convince you that they can fix it , it can at least give you some real data to look at

But if you are not having any operational problems , you not likely have clogged convertor , they last a very long time , you would most probably be getting some check engine codes that are related to it , I really doubt that only 120 k miles would be bad cat .
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Re: Gas mileage increase without catalytic converter

Postby cowboydan » August 18th 2011, 2:11am

do remember, alot of issues stemming from a bad cat usually go unnoticed untill the engine stops. if a cat is rattling, it is likely plugged. an engine will not stall with a cat that is rattling. i know this cause mine rattled badly, and i still got better than average milage. one day the rattling stopped and i had thought that it would die. it never did, so i then thought it was wedged and it was. now i have some debre inside my muffler and it makes some noise....oh well. i will never get it out, and i'm not replacing the muffler anytime soon. a good cat test should be no more than 2psi. any more means it is plugging up.
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Re: Gas mileage increase without catalytic converter

Postby vangogo » September 21st 2011, 5:04pm

I have not tried this myself, but I remember reading that you can test a cat with an infrared thermomemeter, If I recall the temp on a good cat will be about 100 degrees hotter at the output end than the intake end. If anyone knows more about this tecnique please correct me...or maybe even google it for more info.
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Re: Gas mileage increase without catalytic converter

Postby cowboydan » September 24th 2011, 12:36am

it only works if you can get your hands on an infrared thermometer (not too cheap last time i checked). best test if your engine is running badly, pull your sensor. if it runs better, it's your cat. or have it pressure tested at a muffler shop.
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Re: Gas mileage increase without catalytic converter

Postby AstroWill » September 26th 2011, 2:59am

Those infrared thermometers have come down in price a lot, I think harbor freight has them for $20 these days.
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