3.73 vs 4.10 - Page 2 - JeepForum.com
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post #16 of 20 Old 04-21-2013, 07:06 PM Thread Starter
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Thanks... I think I'm going with 3.73s... I realize my 258 was not built for power and running my RPMs close to 3000 while on the hwy is not very smart or suitable for my +30 year old motor.

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post #17 of 20 Old 04-21-2013, 07:56 PM
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Originally Posted by firzout View Post
Thanks... I think I'm going with 3.73s... I realize my 258 was not built for power and running my RPMs close to 3000 while on the hwy is not very smart or suitable for my +30 year old motor.
You'd be spinning 2500 rpm @ 70 mph with 4.10 gears. With 3.73 gears it would be 2250 rpm. Not alot of difference there and not drastic enough to affect that sweet spot for cruising. But thats just my $0.02.

'84 CJ-17: 17" stretch, locked Toy axles, 5.5" lift, FI, AX15, D300 w/twin sticks, boatsides & junk.
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post #18 of 20 Old 04-21-2013, 09:03 PM
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I'm running 4:10, automatic, 4.2L, and unfortunately, lockers front and rear, I do off road, but don't care for lockers, rather have regular posi.. anyway, 33" tires get me right down the road, not sure of the RPM at any given speed, but.... I just bought a TH700RE that will give me a lower first gear and overdrive last gear..

I want to die in my sleep like my grandfather, not screaming in terror like the passengers in his JEEP!...
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post #19 of 20 Old 04-21-2013, 09:58 PM
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I just installed 4.10's and have 31's. Power is great. no pushing the throttle to go up hills. at 75 at 2800 rpm. I do go off road but 90% is on road.... since I love my CJ so much. So I do like the 4.10s I would recommend them for future upgrades. I havent noticed any real change in fuel economy since i went from a 3.08 to the 4.10's If you got to 33's, it would run perfect

Some people are like slinkeys, good for nothing but bring a smile to your face when pushed down a flight of stairs
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post #20 of 20 Old 04-21-2013, 09:59 PM
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Originally Posted by Ripper3494 View Post
Yep. Depending on where your engine gets its power though 4.10s could potentially give you better MPGs. The engine has a sweet spot that it likes to run at
This is correct. And when you run the gear ratio calculator remember that 33" tires are not 33" in diameter. Use 32.5" in the calculator. And a T5 came in two flavors. The most common one had a 0.86 ratio 5th gear but some of them had a 0.76 ratio 5th gear. I had one of the latter for a while. If you lug an engine (where it is running so low in the rpm range that it can't push the vehicle) you can definitely lower your gas mileage. I ran 4.30 gears with my .76 ratio T5 and 33s. If I had gone any lower numerically with the gears I would not have been able to use 5th gear. But then I live at 7000 ft.
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