Better gearing for the 2.5?

donsYJ

donsYJ

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Hey everyone, before I get into my question (which is probably dumb), I just want to give a brief history of my YJ (and my possible routes I can go).

I have a 1989 YJ my grandpa bought in 2003. It has 0 rust, a 4 year old repaint, brand new 4cyl (TBI), 30 inch Toyos, new top, seats, steering wheel, and I'm about to put a new steering shaft bearing repair kit in.

I've been contemplating a few things for the past few months. With gas going back up, I've been driving my sierra and my mustang all the time. I rarely drive my jeep and when I do I tow it somewhere (I live at least 30 minutes from any town). I know I get poor fuel economy, and I know that older cars from the 60s and 70s had higher gearing such as 3.14s and 3.42s such as my 96 sierra. I've been playing around with the idea of swapping in a 3.55 or 3.73 gearing into the YJ. Problem is I have no resources on this topic. I don't care that it's slow, I just don't want the engine screaming at 3000rpm in my ear driving long distances anymore and sucking gas more than necessary. Its important to note this jeep is fairly restored and is not abused as an offroader or will it be used as such. Any tips or links to a parts store that sells gearing for my YJ would be greatly appreciated. Thank yall.
 
donsYJ said:
Hey everyone, before I get into my question (which is probably dumb), I just want to give a brief history of my YJ (and my possible routes I can go).

I have a 1989 YJ my grandpa bought in 2003. It has 0 rust, a 4 year old repaint, brand new 4cyl (TBI), 30 inch Toyos, new top, seats, steering wheel, and I'm about to put a new steering shaft bearing repair kit in.

I've been contemplating a few things for the past few months. With gas going back up, I've been driving my sierra and my mustang all the time. I rarely drive my jeep and when I do I tow it somewhere (I live at least 30 minutes from any town). I know I get poor fuel economy, and I know that older cars from the 60s and 70s had higher gearing such as 3.14s and 3.42s such as my 96 sierra. I've been playing around with the idea of swapping in a 3.55 or 3.73 gearing into the YJ. Problem is I have no resources on this topic. I don't care that it's slow, I just don't want the engine screaming at 3000rpm in my ear driving long distances anymore and sucking gas more than necessary. Its important to note this jeep is fairly restored and is not abused as an offroader or will it be used as such. Any tips or links to a parts store that sells gearing for my YJ would be greatly appreciated. Thank yall.
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It should have 4.10s in it now. A cheaper and much easier approach would be to put on some taller tires. Changing the gears is going to be much more expensive, especially if you need to pay to have the work done. It is not a beginner project. Just my opinion.
 
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I would highly suggest scrapping this idea and possibly recommend going the opposite direction with smaller tires and higher (stock) rpm. Taller gearing/lower rpm often does not equate to better fuel mileage. Fuel mileage is tied directly to load, which is how much throttle you need to overcome the load and keep the vehicle moving. In many cases, the lower gearing is better because you need less pedal to maintain speed, despite the higher rpm. You most likely would not see an mpg increase going to 3.55 or 3.73, if you did it would be so minor that it would take an extremely long time to pay for itself. If you did not see an mpg increase, you would be kicking yourself for a now even more gutless setup.

60s and 70s vehicles are not really relevant. Things were different back then, V8s were often the engine of choice and everything was carbureted. Almost nothing had overdrive and so tall axle ratios were the way things went.

You would actually probably get better mpg by going back to 205/75R15 or 215/75R15, despite that turning higher rpm than you're turning now. That was stock, after all. For the record, 3,000 rpm is not "screaming" either, unless a loud muffler is installed and making a bunch of racket. 3,000 isn't specifically sucking the fuel either, it might in some cases but some of my best mpg has been at 3000 around 65-70 getting 18-19 mpg.

Best thing for fuel economy is low speed, and small tires. 60-65 mph on a bone stock 4 cylinder would probably do 20 mpg easy unless something is wrong. But nobody wants to drive 65 (myself included). When you push 70-75, mpg drops off due to wind, not rpm. Wind is not linear, you get a lot more of it at higher speed and it really kills fuel usage unless the wind is pushing you.
 
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machoheadgames said:
I would highly suggest scrapping this idea and possibly recommend going the opposite direction with smaller tires and higher (stock) rpm. Taller gearing/lower rpm often does not equate to better fuel mileage. Fuel mileage is tied directly to load, which is how much throttle you need to overcome the load and keep the vehicle moving. In many cases, the lower gearing is better because you need less pedal to maintain speed, despite the higher rpm. You most likely would not see an mpg increase going to 3.55 or 3.73, if you did it would be so minor that it would take an extremely long time to pay for itself. If you did not see an mpg increase, you would be kicking yourself for a now even more gutless setup.

60s and 70s vehicles are not really relevant. Things were different back then, V8s were often the engine of choice and everything was carbureted. Almost nothing had overdrive and so tall axle ratios were the way things went.

You would actually probably get better mpg by going back to 205/75R15 or 215/75R15, despite that turning higher rpm than you're turning now. That was stock, after all. For the record, 3,000 rpm is not "screaming" either, unless a loud muffler is installed and making a bunch of racket. 3,000 isn't specifically sucking the fuel either, it might in some cases but some of my best mpg has been at 3000 around 65-70 getting 18-19 mpg.

Best thing for fuel economy is low speed, and small tires. 60-65 mph on a bone stock 4 cylinder would probably do 20 mpg easy unless something is wrong. But nobody wants to drive 65 (myself included). When you push 70-75, mpg drops off due to wind, not rpm. Wind is not linear, you get a lot more of it at higher speed and it really kills fuel usage unless the wind is pushing you.
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Thank yall for the help!! I drive almost 25 miles to work and 25 miles back home. I'm barely getting 14 mpg. The motor has decent power, and it's only got 12k miles on it since I swapped it. Is there anything other than tires I could do for fuel economy on the 4cyl? If not it's ok, I'll just keep towing it with my truck places lol
 
i agree with machoheadgame,keep it stock as much as possible, a good basic tune-up, a tire change, and drive at a speed that meets your condition will save you some money, time, good luck and safe driving.
 
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