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Old 09-25-2012, 10:43 PM   #1
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Talking Ratio / Engine upgrade

Just bought our first Jeep. 95 YJ Wrangler 2.5L.

1. Ratio on the transfer case says 272 and I bought it with 33's with a 2 1/2 lift I think. Would increasing the ratio help with gas mileage cuz we are getting about 13mpg?

I am also thinking increasing engine size to at least a 6 or maybe even an 8 if feasible. I was told a GM 4.3L would be perfect for a 6 cyl on the YJ Wrangler but not sure. Not to mention I think I am losing compression on #3 after the water pump went out and it was drove hot for about 2 miles before she got it home.

I know there are a lot of issues here.

Any input would be greatly appreciated.

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Old 09-25-2012, 10:44 PM   #2
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Obviously not a master mechanic, but I recently rebuilt my boat motor which is a mercury 3.0L inline-4 after losing compression between 1-2 and it runs great now.....

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Old 09-25-2012, 11:37 PM   #3
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If you don't want to do a motor swap, you can always put 4.88 gears in the axles. I did that with my 4 cyl on 33s and it is almost as good as stock. Now that it is not my DD I am thinking of going with 35s. I can actually say I like my 2.5, it's just the weak ass paper weight behind it that I am not too fond of.
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Old 09-26-2012, 04:54 PM   #4
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The ratio that is on the transfer case is a 272:1, which is standard for a New Process 231 t-case.

This number however is not the ratio of the gears in your rears. A stock YJ with a 4cyl motor will have 4.10:1 gears in it. Switching these to 4.88's will definately improve but dont expect miracles for gas mileage.

You stated you were getting 13mpg...thats about average. I have seen them as low as in the single digits for gas mileage, depending on the terrain that you drive in and how heavy your right foot is. Even with the new gears, I wouldn't look for more than a few miles per gallon increase.

And the cost offset can never be regained from better mileage. Besides, have you re-adjusted your figures for actual miles traveled vs. miles on the odometer? With the larger tires, when you are going 49, you are actually going 55, which is about a 10 % difference, so your mileage just went up to a 14.3mpg, and that is in the parameters for a stock 4cyl motor.

If you are worried about mpg, buy a rice grinder car, you have a Jeep, its about as aerodynamic as a brick, sooooo, fuel mileage is not going to be a high number. If you really want to keep the Jeep and try and get decent mpg, go back to a stock tire....215/75R/15....they are about 5 inches shorter than the 33's and your fuel mileage will come back up. Unfortunately you cant have both, big tires and high numbers in the MPG department.
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Old 09-26-2012, 05:00 PM   #5
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Just going off of information spread about the boards, you should expect about 16-18mpg with 33" tires and the appropriate gearing (4.88). I am averaging right around 19-20mpg with quality gasoline with my 4 cylinder 5 speed, on 29" tires. Buying a quality gasoline like Arco, Exxon/Mobile, or Chevron makes a BIG difference. You do get what you pay for, I've noticed an MPG increase over using the cheap stuff.
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