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#1141763 - 05/01/08 05:55 PM Removing Catalytic Converter = Better Gas Mileage
Chuck1986 Offline


Registered: 07/16/05
Posts: 420
Loc: Scottsdale, AZ
OK, here's a serious solution to the rising gas prices:
Replace your catalytic converter with a stainless steel straight pipe and watch your MPGs soar. If you want to take it a step further, remove your pre-cats (if your car has them) and also remove the stock airbox and get a K&N air filter (or aftermarket intake) as well.

I did this fix on my Mitsubishi Eclipse GT and I'm consistently getting 25-27 mpg (10% highway) which far supercedes the EPA estimated 20 mpg. Try it, it works!

Oh and if you need to cheat OBD-II emissions testing: Place a spark plug non-fouler between your secondary O2 sensors - it will cause a "cooler" reading, tricking the sensor to think the cat is still there - it goes by exhaust temperature to determine if the cat is functioning.


Edited by Chuck1986 (05/01/08 05:56 PM)
_________________________
2001 Mitsu Eclipse GT 70k miles
Castrol Edge 5w-30, G-05, Redline C+ ATF
Wouldn't trade her for a new Eclipse

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#1141764 - 05/01/08 05:59 PM Re: Removing Catalytic Converter = Better Gas Mileage [Re: Chuck1986]
Chuck1986 Offline


Registered: 07/16/05
Posts: 420
Loc: Scottsdale, AZ
Disclaimer: The above post is for entertainment purposes only.
_________________________
2001 Mitsu Eclipse GT 70k miles
Castrol Edge 5w-30, G-05, Redline C+ ATF
Wouldn't trade her for a new Eclipse

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#1141766 - 05/01/08 05:59 PM Re: Removing Catalytic Converter = Better Gas Mile [Re: Chuck1986]
simple_gifts Offline


Registered: 07/26/04
Posts: 8701
Loc: Middlesex County CT
You could just slow down.


Edited by simple_gifts (05/01/08 06:00 PM)
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#1141769 - 05/01/08 06:01 PM Re: Removing Catalytic Converter = Better Gas Mile [Re: simple_gifts]
Chuck1986 Offline


Registered: 07/16/05
Posts: 420
Loc: Scottsdale, AZ
 Originally Posted By: simple_gifts
You could just slow down.


I always keep my speeds around 50mph - which is optimal for fuel economy on this engine.
_________________________
2001 Mitsu Eclipse GT 70k miles
Castrol Edge 5w-30, G-05, Redline C+ ATF
Wouldn't trade her for a new Eclipse

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#1141775 - 05/01/08 06:06 PM Re: Removing Catalytic Converter = Better Gas Mile [Re: Chuck1986]
JHZR2 Offline



Registered: 12/14/02
Posts: 33282
Loc: New Jersey
 Originally Posted By: Chuck1986

Oh and if you need to cheat OBD-II emissions testing: Place a spark plug non-fouler between your secondary O2 sensors - it will cause a "cooler" reading, tricking the sensor to think the cat is still there - it goes by exhaust temperature to determine if the cat is functioning.


Huh???!!? A temperature reading???

IIRC, an O2 sensor is effectively a solid oxide fuel cell, and thus produces a voltage (its reading) based upon oxygen ions present in the gas stream. Problem is, the ceramics used are only conductive at high temperatures...

So temperature enables the electrochemical reaction to occur... but temperature is not what the sensor is reading.

Someone please correct me if Im wrong.

JMH

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#1141779 - 05/01/08 06:08 PM Re: Removing Catalytic Converter = Better Gas Mile [Re: JHZR2]
Chuck1986 Offline


Registered: 07/16/05
Posts: 420
Loc: Scottsdale, AZ
 Originally Posted By: JHZR2
 Originally Posted By: Chuck1986

Oh and if you need to cheat OBD-II emissions testing: Place a spark plug non-fouler between your secondary O2 sensors - it will cause a "cooler" reading, tricking the sensor to think the cat is still there - it goes by exhaust temperature to determine if the cat is functioning.


Huh???!!? A temperature reading???

IIRC, an O2 sensor is effectively a solid oxide fuel cell, and thus produces a voltage (its reading) based upon oxygen ions present in the gas stream. Problem is, the ceramics used are only conductive at high temperatures...

So temperature enables the electrochemical reaction to occur... but temperature is not what the sensor is reading.

Someone please correct me if Im wrong.

JMH


Gotcha, that makes sense.
In any case, placing a spark plug non-fouler between your SECONDARY O2 sensors and the insertion point has prevented a SES light for thousands of miles on my car.


Edited by Chuck1986 (05/01/08 06:09 PM)
_________________________
2001 Mitsu Eclipse GT 70k miles
Castrol Edge 5w-30, G-05, Redline C+ ATF
Wouldn't trade her for a new Eclipse

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#1141785 - 05/01/08 06:17 PM Re: Removing Catalytic Converter = Better Gas Mile [Re: JHZR2]
DmanWho Offline


Registered: 07/26/07
Posts: 578
Loc: Oregon
I don't know if it is helping the gas mileage, but I removed cat. #2 on the SX4. Not the pre-cat, as the O2 sensors have it surrounded, and I didn't know "how not to" throw a code.

I also replaced the stock intake box with a more direct CAI type intake. I did retain the stock air filter though, because of my fear of elevated Si values.

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#1141786 - 05/01/08 06:19 PM Re: Removing Catalytic Converter = Better Gas Mile [Re: Chuck1986]
JHZR2 Offline



Registered: 12/14/02
Posts: 33282
Loc: New Jersey
That is an interesting finding...

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#1141791 - 05/01/08 06:25 PM Re: Removing Catalytic Converter = Better Gas Mile [Re: JHZR2]
MGregoir Offline


Registered: 08/30/07
Posts: 1784
Loc: Bonnyville, AB
On a Crown Vic, leaving the pre-cats but pulling the mains yields nearly a 40 horsepower gain according to a guy I know who specialized in "upgrading" ex-cop cars.

He had some extremely fast rides.

I know on a lot of vehicles if you pull the catalyst, the ECU reads it as out of range for a certain amount of time then goes back into closed loop off the signals it does get regardless of the idiot light. A guy I know does that to his late model work trucks.

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#1141832 - 05/01/08 07:49 PM Re: Removing Catalytic Converter = Better Gas Mile [Re: MGregoir]
MrCritical Offline


Registered: 08/04/07
Posts: 2340
Loc: La.
On my ex-Nissan Spec V, the pre cats were made into the exhaust manifold and had a nasty habit of coming apart and being sucked into the engine.

Cleaned them out (for off road purposes only). Perceived horsepower up tremendously. Mileage a little better, probably would have been even better if not turning over the tires in first and second gear.

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#1141870 - 05/01/08 08:19 PM Re: Removing Catalytic Converter = Better Gas Mile [Re: MrCritical]
bdcardinal Offline


Registered: 06/03/05
Posts: 6342
Loc: Santa Barbara, CA
on my mustang o put on a offroad (no cats) Bassani X pipe. the stock midpipe was a H and had 6 cats on it. sounded a lot better. gained a decent amount of power. also the gas mileage gains werent there, but i tended to get on it a lot more without the cats.

o and if you have a ford, you can buy MIL eliminators that plug inbetween the cat monitor and the wiring harness that trick the computer into thinking cats are there. you can also turn off the cat monitor in the PCM with an aftermarket dyno tune.
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#1141898 - 05/01/08 08:48 PM Re: Removing Catalytic Converter = Better Gas Mile [Re: MGregoir]
chuckerants Offline


Registered: 10/14/06
Posts: 227
Loc: Phoenix, AZ
A Crown Vic has about 200 Rear Wheel HP stock - yes even PIs.

So your friend told you deleting the cat yielded 40 HP? Tell your friend he's full of it.

A cat con that is working normally has very little effect on a car's HP and in turn MPG.

I've had my Miata on the dyno as well as having dynoed other Miatas and the ones with working cats gained only about 2~3 HP without the cat. The ones with plugged cats (like my car) gained 10~15 HP without the cat. This is all on Miatas that were being boosted to almost twice the HP from stock.

The bottom line, removing the cat has very little (positive) affect on performance. If you want your car to stink like rotten eggs and have an annoying CEL, go for it.

 Originally Posted By: MGregoir
On a Crown Vic, leaving the pre-cats but pulling the mains yields nearly a 40 horsepower gain according to a guy I know who specialized in "upgrading" ex-cop cars.

He had some extremely fast rides.

I know on a lot of vehicles if you pull the catalyst, the ECU reads it as out of range for a certain amount of time then goes back into closed loop off the signals it does get regardless of the idiot light. A guy I know does that to his late model work trucks.


Edited by chuckerants (05/01/08 08:52 PM)
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#1141945 - 05/01/08 09:39 PM Re: Removing Catalytic Converter = Better Gas Mile [Re: chuckerants]
Jonny Z Offline


Registered: 06/03/05
Posts: 1251
Loc: Austin, TX
No one mentioned the pollution?
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02 Camry SE 4 cyl 5sp manual. 120K. Vavoline MaxLife Blend 5W30 + Purolator Classic / Redline MT90 / Michelin HydroEdge

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#1141949 - 05/01/08 09:45 PM Re: Removing Catalytic Converter = Better Gas Mile [Re: chuckerants]
BuickGN Offline


Registered: 10/18/07
Posts: 3756
Loc: CA
Different cars are different. My TL uses 1200 cell precats I believe and a 300 cell single cat. The exhaust leaves the head (only one exhaust port) and makes a 90 degree turn in the course of about 1.5" straight into the precats. Deleting all three shows close to 30hp at the wheels and about 4mpg. My third cat is gutted and I just ordered the precat deletes.

On the GN, there was no single cat that flowed enough. I tried a Random technologies cat and lost 8psi boost and 10mph through the 1/4.
_________________________
84 Buick GN. 10.60@127 old times. 602hp 620lbs.
06 Acura TL. Lots of suspension and brake mods.

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#1141965 - 05/01/08 10:06 PM Re: Removing Catalytic Converter = Better Gas Mile [Re: Jonny Z]
Duffman77 Offline


Registered: 12/21/06
Posts: 561
Loc: Alberta, Canada
 Originally Posted By: Jonny Z
No one mentioned the pollution?


I thought about it, but after so many internet p*ssing matches, I have tired a bit and realized there is little point with some topics.


Edited by Duffman77 (05/01/08 10:06 PM)

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