Final Drive Ratio (1 Viewer)

[thetoyotaman]

My '82 FJ40 with 3.73's has a final drive rpm of about 2500 @55mph stock. My engine rebuilder has said that he's wouldn't be comfortable running sustained rpms beyond 2800 rpm. That being the case, would a 2F comfortably drive at 75mph at 2800rpm?

Would my clutch hold up to such a tall final drive with the 4 speed? I'm thinking starting off would be harder on the clutch possibly.

 

[Fuzzy Logic]

Up grade to a H55 5spd. (problem solved)

 

[Josie'sLandCruiser]

Hi All:

If the 2F is only turning 2800 RPM at 75 mph I would not be worrying about the engine, but about the steering and brakes!

If you are worried about the first gear ratio being too high, the H41 four-speed would be an easy swap for your rig. The H41 features a 4.9 to 1 first gear, versus the 3.55 to 1 first gear of the H42.

Good luck!

Alan

 

[Mark W]

You have no worries either for your clutch or your engines ability to sustain those rpms...


none whatsoever


Mark...

 

[thetoyotaman]

So, if 2800 rpm is a good target to hit for 75 mph I wonder if it would have a tough time going over the mountain passes here in Montana.

 

[FF LC FREAK]

You need a different engine rebuilder if he is worried about 2800 RPMs. Like I posted in another post yesterday, the max HP is rated at 3600 RPMs.

 

[Rice]

You have no worries either for your clutch or your engines ability to sustain those rpms...


none whatsoever


Mark...

... X2!

 

[ken_79-fj40]

I ran mine at 2700-2900 for extended periods just about every time I drove it. My commute to work is 1/4 mile from my house to 65-75 MPH traffic for 40 miles and then another 5 or so at around 40. Upon teardown of my 2F which I am currently rebuilding it has been discovered that my head had a huge crack in the # 5 combustion chamber, probably the whole time i've owned. So if a tired engine with essentially no ring sealing in one cylinder burning water can turn these rpm's without blowing up I wouldn't worry about a fresh one. I can't wait to get mine going again fully balanced with a shaved head and a 262 duration Delta cam. It's gonna be sweet.

 

[thetoyotaman]

I've been thinking through some off these issues of final drive ratio, tires, and rpms. My engine builder didn't push the idea of 2800 rpm on me, I asked him what he thought would increase durability from his experience if I wanted to drive it all day long on the highway. I don't know that I will, probably wont, but just want to know. He's a great guy with 35 years of experience, working from the ground up and then buying the business. From his experience he has rebuilt F's, 2F's, 3FE's running around in Montana that have failed from excessive sustained rpm on the highway that he has attributed to the massive rotating assembly not being so well balanced from the factory and basically vibrating to death. I'm just looking for the best ways of operation to maximize durability since I hope not to do this again for a very long time. I'm certainly going to have fun with the rebuld though. Balanced assembly, shaved head, Delta cam. Thanks!

 

[Mark W]

He is wrong on this issue.


These engines fail from inadequate oiling, not from vibration... the balancing could be better, and on any one at a time build, (as opposed to a productionline build) it should be.

But vibration does not cause problems in these engine series. I have build more than a few of these myself... at one time I had 1O engines on hand which had failed due to lubrication issues... I have seen about a half dozen which grenaded due to failed rop boltsd (too high an RPM). I have a few modified 2 and 3Fs in rigs now scattered around the country, and more running locally.

Keeping the RPM low will help any engine last longer... stresses climb geometrically with RPM increase, not linearly. But I and many others have run 2Fs at and over 3000 for hours at a time for years... they will take it just fine... an FJ60 on stock tires is gonna run 3000 at abut 65mph... LOTS of people run these ring at this speed on the highways of America for years... and faster.

FWIW, the diffs are 3.70:1 in Cruisers, not 3.73:1 (37 teeth on the ring and 10 on the pinion)


Anyway, I would not worry to much about your engine standing up to this rpm range so long as you have good bearing clearances and decent oil.


Mark...

 

[thetoyotaman]

Cool! Thanks for the heads up. Anything I should do on the oiling system while rebuilding? What do you feel then is the best highway rpm @75?

By the way, do you like 3B's and H55F's? Do you run them?

 

[Brian in Oregon]

I thought concerns about sustained RPM's in the 2800 to 3000 RPM range on an I-6 went away when flatheads became extinct.

 

[Vicm]

75 MPH is roughly 130 km/hr,
I would be concerned more about my life than the life of my engine....
3B with 5sp , are you joking?? Who wouldn't like that.

 

[Mark W]

A 3b with an H55F would be cool.... in a country where you could get parts.... where the parts stores or the dealership even have the correct parts listed.

That is not the USA.


There is a a number of things that you can do to the oiling system... but in a late model 2F like yours... I would simply make sure your pump is in good shape and that your bearings are overly loose.


You are limited in any chasing of ideal cruise RPM.... you already have the tallest gears you can get... Tires of about 35 inches are the most i would run with these gears for acceptable performance on the road. With the splitcase T/C you will do okay for all around general offroad use too. but no taller for either use IMHO.

This rig was never designed with North American high speed highway use in mind. Just the nature of the beast.

Really 75 MPH for routine use... I would find another rig... you are asking the '40 to do a job it can do, but was never meant for.


Mark...