Recommended Ring and Pinion Gears (1 Viewer)

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G

Gearhead

Joined
Jan 8, 2013
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Location
Pleasant Hill OR.
Hello All,

I have a 71 FJ40 with a 2UZ and an H55f on 35's. The truck drives fantastic but 5th gear is almost unusable, nobody needs to go 100mph in a spring over 40! The current ring and pinions are 4.10. What would you recommend? And since everyone likes a picture...

1690398943599.png
 
4.88s is what I'd do.
 
Tigerstripe40 said:
4.88s is what I'd do.
Click to expand...
What is your thought process behind 4.88's? I was thinking 4.56 or 4.88 would be about right but would like to know if there is a mathematical formula? Sweet spot for engine RPM HP and Torque, transmission transfer case ratio, ring and pinion and finally tire size. What's right for an F or 2F may not be ideal for 2UZ? I'm just trying to understand the best fit. Thank you.
 
Gearhead said:
What is your thought process behind 4.88's? I was thinking 4.56 or 4.88 would be about right but would like to know if there is a mathematical formula? Sweet spot for engine RPM HP and Torque, transmission transfer case ratio, ring and pinion and finally tire size. What's right for an F or 2F may not be ideal for 2UZ? I'm just trying to understand the best fit. Thank you.
Click to expand...

Those formula are out there and I am sure you can google them.

But in ~25 years of doing this, nearly everyone I have encountered that did 4.56's, be it with an F/2F, SBC, LS, or UZ almost always regretted running 4.56's instead of 4.88s.

And, while you're in there, add at least a rear ARB, if not ARBs F/R. That will help with offroad ability and resale down the road if you ever decide.
 
So on your rig currently at 80mph in 5th gear, you're at 2660 rpm. Peak torque on the 2UZ is farther up at 3400 rpm. With 4.88s at 80mph you're a bit closer at 3166 rpm. 5.29 would get you right to 3400, but that gets to be more a preference than anything. At 4.88, I'd be happy. If going through all this work and wanting a bit deeper gearing for crawling, 5.29 might be the ticket
 
You can find a rpm calculators all over the internet, for potential highway rpms and speed and actual measured tire size. Then I'd suggest do the math for what you currently have in all gears 1st thru 5th in high and low range and make a chart. You're not going to be concerned with speed and rpms for off road. Then do the same for the diff ratios you're considering. Comparing what you currently have to the potential ratios is helpful. You know what gears you currently like in high and low range when trail riding. My trail 40 is runs 85:1 in 1st low range and 4 wheel disc's can't stop it at idle. It has a sm420 with a 7.05 1st gear, 2.46 low range and 4.88s in the diffs. I run a sbc 350. At 60mph it's around 2800rpms. To me it's comfortable. I built my street, light trail 40 runs around 1800rpm at 65mph for fuel mileage, with a sbc, nv4500, 3.70:1 diffs and 33" tires. 1st low range is 46:1, which is barely adequate.
 
Tigerstripe40 said:
Those formula are out there and I am sure you can google them.

But in ~25 years of doing this, nearly everyone I have encountered that did 4.56's, be it with an F/2F, SBC, LS, or UZ almost always regretted running 4.56's instead of 4.88s.

And, while you're in there, add at least a rear ARB, if not ARBs F/R. That will help with offroad ability and resale down the road if you ever decide.
Click to expand...
This will be used as a light trail rig and I'm leaning to the 4.88. I really appreciate the response and opinions!
 
AgentOrange said:
So on your rig currently at 80mph in 5th gear, you're at 2660 rpm. Peak torque on the 2UZ is farther up at 3400 rpm. With 4.88s at 80mph you're a bit closer at 3166 rpm. 5.29 would get you right to 3400, but that gets to be more a preference than anything. At 4.88, I'd be happy. If going through all this work and wanting a bit deeper gearing for crawling, 5.29 might be the ticket
Click to expand...
As I noted, this will be a light trail rig and 4.88 should be good enough. But I will still play with the calculator and change my mind a few times :rolleyes:
 
Gearhead said:
This will be used as a light trail rig and I'm leaning to the 4.88. I really appreciate the response and opinions!
Click to expand...
UZ + H55F is actually one of the directions I would like to go with my FJ40.
I have a 2000 tundra to act as a donor rig for the UZ, and my FJ40 already has 4.88s.

The other option I am thinking about is a 1HD-FT with a Yanmar pump.
 
Tigerstripe40 said:
UZ + H55F is actually one of the directions I would like to go with my FJ40.
I have a 2000 tundra to act as a donor rig for the UZ, and my FJ40 already has 4.88s.

The other option I am thinking about is a 1HD-FT with a Yanmar pump.
Click to expand...
A guy needs two 40's at least! One diesel, one gas, daily driver hard-core ect.....
 
Gearhead said:
A guy needs two 40's at least! One diesel, one gas, daily driver hard-core ect.....
Click to expand...

I want to build what Toyota should have built as the FJ Cruiser.
One 40 to rule them all. :D
Take a look at a FJ Company GRJ-43 and that gives an idea.
 
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