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Old 02-23-2012, 02:59 PM   #1
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Exhaust System and Gas Mileage

I was watching an episode of Geerz on the Speed Network and it was talking about upgrades you can make to improve gas mileage. Stacy David stated that the engine is just an "air pump", which brings in air, adds fuel, and then expells air through the exhaust. To increase gas mileage, you would want to increase the air flow. He suggested taking the stock exhaust out and replacing it with one such as Cherry Bomb. This got me thinking.....what do you guys think the best effective, bang for your buck, exhaust system would be best? I am not so much worried about the sound as I am the performance. I am interested in what everyone thinks!

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Old 02-23-2012, 03:00 PM   #2
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Flowmaster 40

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Old 02-23-2012, 03:10 PM   #3
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To increase gas mileage, you would want to increase the air flow.
There is alot more to it than that. Increasing air flow means increasing more fuel...otherwise you will have a lean condition and have a piston melt down.

Another thought...if that were true, don't you think a 6" dia intake and exhaust pipe be better? Apparently gas engines need some back pressure...optimal air velocity seems to be important.
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Old 02-23-2012, 03:30 PM   #4
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I'd start with headers, stock headers are only there to direct the exhaust they were not designed for performance and mileage.

Good headers, then think about muffler/cat and pipes
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Old 02-23-2012, 04:02 PM   #5
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I do the usual to mine; CAI, Borla header, cut the cat out...Flowmaster 40. Sounds good..and noticable gains. And no i couldnt care less bout green peace and they dont do emissions tests here. Just stating what i do :P
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Old 02-23-2012, 04:04 PM   #6
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I do the usual to mine; CAI, Borla header, cut the cat out...Flowmaster 40. Sounds good..and noticable gains. And no i couldnt care less bout green peace and they dont do emissions tests here. Just stating what i do :P

Sounds perfect, did you notice much change in mileage & performance?
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Old 02-23-2012, 04:08 PM   #7
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I do the usual to mine; CAI, Borla header, cut the cat out...Flowmaster 40. Sounds good..and noticable gains. And no i couldnt care less bout green peace and they dont do emissions tests here. Just stating what i do :P
X2 on the statement and x2 for the great id tag
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Old 02-23-2012, 04:12 PM   #8
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You will notice quite a bit in the performance range...but as usual..if your heavier on the pedal you'll you will lose as much as you gain. IF you drive "normally", which i don't, i'm sure would help the mileage a bit. But even runnin 36's and 38's i never get much less then 15 or so mpg.
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Old 02-23-2012, 04:54 PM   #9
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15 MPG with 36's and 38's?? I have 31's, everything else stock and barely get 10-11. I have a 2006 4.0L 6 speed with 37k miles. What should I be looking at? Tire pressure is at 28.
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Old 02-23-2012, 05:15 PM   #10
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15 MPG with 36's and 38's?? I have 31's, everything else stock and barely get 10-11. I have a 2006 4.0L 6 speed with 37k miles. What should I be looking at? Tire pressure is at 28.
I'm gettin 17 with my 04 rubi with 4:11s and 33s... and 5 spd... Keep your foot out of it, learn to shift progressively .. Keep it under 68 mph... You should be gettin 17 easy with your 3:73s...
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Old 02-23-2012, 05:32 PM   #11
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15 MPG with 36's and 38's?? I have 31's, everything else stock and barely get 10-11. I have a 2006 4.0L 6 speed with 37k miles. What should I be looking at? Tire pressure is at 28.

Take it out of 4 low. Seriously 10? I have a 06', 6 cyl and 6 speed and get 15-18 all stock. Are you calculating this or using a phone app?? Try real calculating.

If someone bought a Jeep for fuel mileage, you bought the wrong vehicle.
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Old 02-23-2012, 05:52 PM   #12
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I gotta say I have a 06 4.0 auto and am getting 10-12 mpg. I do not drive crazy "AT ALL" and am very disappointed in my MPG. I did not buy my Wrangler for gas mileage but come on this is nutz. All stock.
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Old 02-23-2012, 06:26 PM   #13
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I definitely did not buy it for the gas mileage. This is my play toy not my DD. I don't drive aggressively at all. I track the mileage by filling up first, calculate miles driven, then fill back up and see how many gallons it took. Granted, seeing that I have 31's, I cannot replace the speedo gear so my speedometer is about 10% off which makes my odometer off. I don't think that would case a 5 mpg difference in mpg would it?
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Old 02-23-2012, 06:33 PM   #14
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I did not buy my Wrangler for gas mileage but come on this is nutz. All stock.
Agreed, I would rather spend my money on mods and upgrades instead of gas!!
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Old 02-23-2012, 06:34 PM   #15
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i have an 06 4.0L and 6 speed with 31s and a CAI and get 14 but i am sure it would do better if i drove it right.
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Old 02-23-2012, 06:34 PM   #16
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We can all agree that the poor mpg we are experiencing is not right, but what areas can we look at for issues that may be preventing us from getting better mpg?
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Old 02-23-2012, 06:57 PM   #17
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Try basic tune up like cleaning the air filter, intake system(manifold and throttle body), and new spark plugs. Also try running the tires more in the 30-35psi range and check with the chalk test to see where your tires like to be. You may lose a bit in comfort but less rolling resistance will help. Also fixing the speedo is never a bad idea when you finally find a tire and gear combo you are good with. 10% incorrect is the diff between 20 and 18 mpg. Overall just make sure all fluids and parts from spark plugs to joint grease get changed when they need it.

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