Gear ratio

[etexjeep]

So I've got the inline 6 with roughly 3.5 inches of lift and 33's along with 3.73 gears. What would be the best gear ratio for 40% off road use and a little more pep to her?
Thanks in advance!


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[Lumpy Grits]

I'm run'n 4:88 with a 5-speed, & 33's.
Couldn't be happier!
With your auto, I'd say 4:10 is as 'deep' as you want to go.
LG

 

[DC712001]

I have a '79 with 3.73 ratio and 33-inch tires and mine has plenty of Pep, but, then again,...

I have a AMC 304 V8 with Headers, a moderate aftermarket Cam, 4-BBL Holley Carb and Edelbrock Intake.

Have you tried using a Tire Diameter/Gear Ratio/RPM Calculator:

Calculators

You plug in the proposed Gear Ratio and Tire Diameter and determine what Engine RPM and Speed are your Result of various combinations before you make a change and to help you select.

 

[etexjeep]

Any idea what it would do to my gas milage if I switch to 4.10?


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[gutthans]

It might improve...Depending upon where your torque band is, the 4.10 (as Lumpy suggested) might place you in the 'sweet spot'.

Remember, a stock 3.73 is a 'performance' 6 cyl. gear, at the top of the factory curve. The 4.10 was a mandatory stock gear with the 4 cylinder because of reduced mass (torque) in the driveline...with larger 31-33" tires it replaces the 3.73 when moved over to the stock 6 cyl. So basically, it's likely the best compromise between mileage and power with a 6 cyl and slightly (31 - 33") larger than stock tires.

 

[IOPort51]

when you are running highway speed at 1 to 1 final drive you are about as close to the sweet spot as you can hope for, if like most, your AMC 258 i6 / 4.2l torque peek is 2500-3000.

If you are looking for fuel economy from a CJ I wish you the best of luck, many have tried and many have failed. If, by some chance you do succeed we are all ears and waiting hopefully.

 

[PaRenegade]

So I've got the inline 6 with roughly 3.5 inches of lift and 33's along with 3.73 gears. What would be the best gear ratio for 40% off road use and a little more pep to her?
Thanks in advance!

I have pretty much the same setup, thought you didn't say what tranny, I'll assume it's a T-5 or T-4 like mine. It depends on how you define "pep", low end or high end. I have good low end pep, going thru the gears fairly quick. But at on the highway it's screaming at 65mph. Acceleration isn't too bad at high speeds but it's because your at the higher side of the power curve. My wife also had an 84, same setup except with 3.54 gears and it was a great cruiser on the highway and got great gas mileage. But she also had the T-5 where mine was the T-4. If mine had the OD it might be the perfect combo.
As for low end, I think the 3.73's are right on the edge for 33" tires but work fine. I kinda wish I'd have went with 4.10's but I would suffer even more on the highway (unless I had the T5). So being that your using it 60% on the road, you may have as good as it can be, especially if you have the T5. Maybe you should look more into performance enhancements for the engine rather then changing gears. It's still only a AMC 258 i6 / 4.2l so it will never be a neck snapper, but it can be made to run better. Have you done anything to the stock engine so far?

 

[etexjeep]

I have pretty much the same setup, thought you didn't say what tranny, I'll assume it's a T-5 or T-4 like mine. It depends on how you define "pep", low end or high end. I have good low end pep, going thru the gears fairly quick. But at on the highway it's screaming at 65mph. Acceleration isn't too bad at high speeds but it's because your at the higher side of the power curve. My wife also had an 84, same setup except with 3.54 gears and it was a great cruiser on the highway and got great gas mileage. But she also had the T-5 where mine was the T-4. If mine had the OD it might be the perfect combo.
As for low end, I think the 3.73's are right on the edge for 33" tires but work fine. I kinda wish I'd have went with 4.10's but I would suffer even more on the highway (unless I had the T5). So being that your using it 60% on the road, you may have as good as it can be, especially if you have the T5. Maybe you should look more into performance enhancements for the engine rather then changing gears. It's still only a 258 so it will never be a neck snapper, but it can be made to run better. Have you done anything to the stock engine so far?

I haven't done anything to the engine but mine has the 3 speed auto which I think is T999? It just lugs down when climbing small stuff and I don't care about going super fast.


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[Lumpy Grits]

I stand by my post(#2)and your mileage may go up some.
I know your performance will.
These 6's aren't rockets--
LG

 

[Dan77CJ7]

I haven't done anything to the engine but mine has the 3 speed auto which I think is T999? It just lugs down when climbing small stuff and I don't care about going super fast.


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time for a T-18 ......:drool::drool:

 

[Lumpy Grits]

time for a t-18......:drool::drool:

As long as the crank is drill'd for a pilot bushing.
Seen a couple that weren't---
LG

 

[Saddle Tramp]

As long as the crank is drill'd for a pilot bushing.
Seen a couple that weren't---
LG

I’ve not heard of an AMC I-6 where the crank wasn’t drilled for the pilot bushing but know that pre 1972 AMC V-8s may not be drilled or are a small hole. Maybe the not drilled I-6s are left over cranks from when Rambler was making the motors. (Pre AMC)