1978 FJ40 Transmission Swap

[POPO AGIE]

Since my build is not running yet I have no way to prove the Cummins rpm calculator. I do have experience with the 4 speed and 4:11 axle gears with both the F and 2F motors and it was terrible. I did get it up to 80 a few times when I was late for work out at the Jim Bridger Power Plant. I had installed a tach on the steering column sometime in the late 70s so I have first hand experience with the rpms with F motors.

Once I get the DD gauges installed and the truck can be driven I will see how everything works with the R2.8 and new drive train.

 

[POPO AGIE]

Rpm calculator, 4000 rpm, 4.11 and 35's you would have been going 101 mph.

When it was my daily driver I was running a lot smaller tires then I have installed now. It came with H78R15s and the largest tire I had on it then was a N78-15 Ground Hawgs which was maybe 31" diameter. I never did any calculation for the difference in tire diameters.

I even had a set of Armstrong Norseman's that were 9.50 30R15s it seem to preform all about the same at over 6000 feet pretty poorly.

 

[pb4ugo]

The calculations have nothing to with the engine, it's rpms. There are many calculators. Search rpm calculator, Try randy's . You need to measure your tires. Use a level across the top of the tire and a tape measure. I looked 4.11, 35's 1:1 4th gear at 55mph is 2150rpms. If the h55 is 20% reduction plug in .80.

 

[POPO AGIE]

I will wait and see what it will be when I can drive it.

It wont go anywhere right now with out drive shafts.

 

[EWheeler]

The calculations have nothing to with the engine, it's rpms. There are many calculators. Search rpm calculator, Try randy's . You need to measure your tires. Use a level across the top of the tire and a tape measure. I looked 4.11, 35's 1:1 4th gear at 55mph is 2150rpms. If the h55 is 20% reduction plug in .80.

This one's pretty good.

Gear Ratio Calculator

 

[pb4ugo]

When ever I do major changes to my driveline that effect highway driving i always check rpm calculators for speed, tire size and rpms. I then make charts of all the individual tranny gear ratios and tcase high and low range ratios including ring and pinions. My 1st chart is for what I'm running now. The other charts are for what I'm considering. That way I can compare the results to what I'm already running, especially off road. Like my crawl ratio, 7.05x2.46x 4.88=84.6:1. Imo, the more important ratios are the gear you like to be in for general trail cruising, and what i call my racing gear, which is the abilty to turn the tires under a relatively heavy load. It usually offer great acceleration and deacceleration.

 

[pb4ugo]

This one's pretty good.

Gear Ratio Calculator

Thats great. Yrs ago I did the same thing long hand.

 

[pb4ugo]

I will wait and see what it will be when I can drive it.

It wont go anywhere right now with out drive shafts.

You want to make sure the engine is running within in its power band rpms.

 

[POPO AGIE]

You want to make sure the engine is running within in its power band rpms.

I have a degree in Industrial Maintenance and work on the most powerful engines in the world. I have been a Field Engineer for almost 30 years and have worked on gas, steam and nuclear turbines up to 1500 MWs and as small as being able to lift the rotor with another Millwright in a paper mill.

I have worked on other pieces of mechanical equipment in heavy industry. I have a grasp of engines working in there most efficient power band,

Because of my mechanical knowledge I have worked all over the world.

 

[BullHab]

I'm searching the forums/Google quite a bit and while I know my questions are vague, I'm gaining a lot more knowledge as I go (in no small part because of the helpful responses I've been getting here as well). I've actually changed my plan to be some what like you suggested; use a different car for any trips and work on the FJ in my spare time.

Right now one of the FJ's I'm looking at has had its engine replaced with GM 350 crate engine. I've searched the forums and found plenty of people who put a Chevy V8 and was wondering if this was a common engine replacement, or something I should avoid.

Very common. Works well with the FJ40.

 

[BullHab]

You can find rpm calculators on the internet. If you want accurate info, be sure to physically measure your tires. They are usually shorter than advertised.

I absolutely agree. My 285/75-16 spec out at 32.8 inches. They measure out at 31.75 inches with 32 psi.