MPG difference with 2F engine between 4 speed and h55f 5 speed (2 Viewers)

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

what other reasons?
For a 5 speed conversion? I believe the reasons would be that it allows for a higher top speed and provides a lower first gear.
Are you saying that you have an FJ40 that got 28MPG? If so, was it a diesel, or did you have to push it over a 8% grade for 30 miles to get that?
"Other rig". No Land Cruiser gets 28 mpg, especially a 40!
 
No, don't assume the transmission will improve fuel economy. It's only better for driveability and reduction of rpm at freeway speeds. Note that it is essentially an overdrive, you don't have much oomph in 5th.

Great for folks on the freeway, otherwise the lower 1st is nice on-trail. I think one should weigh the true benefits as many times the H55 isn't needed for many. H42 with 33s (and 35s) is decent tradeoff. I love(d) mine cruising on the interstate very long distance (10+ hour stretches)....but I've done those same stretches with H42 and it did just fine.
 
Last edited:
The best I ever got with the 4 speed in 4 hi was 18 coming home from Jackson Hole, Wyoming most of the time I got 11 which sucked with a 16 gallon tank. In a head wind I could not do 55 unless a truck passed me and blocked the wind.

With the same gears in the axles, R2.8, H55F and the new 29 gallon tank I will be happy with a 600 mile range.
Right forgot about the 2.8. Was thinking you had a magical 2F
 
With 31" tires, 3.70 gears and a H55, the gearing calculator says I'm at 2050rpm in 5th gear at 60mph. Which sounds close enough to reality

My 2F was anemic at best, I'd get 11-13mpg typically.

With the Chinese cummins I get between 20-21 no matter how I drive.
.
A 40 series is a lost cause for milage. You're just plowing through the air.
 
With 31" tires, 3.70 gears and a H55, the gearing calculator says I'm at 2050rpm in 5th gear at 60mph. Which sounds close enough to reality

My 2F was anemic at best, I'd get 11-13mpg typically.

With the Chinese cummins I get between 20-21 no matter how I drive.
.
A 40 series is a lost cause for milage. You're just plowing through the air.
Hold on a second... Chinese Cummins???
 
As mentioned earlier in the responses, lugging too low while cruising will drop you below the efficiency range of the engine and eliminate any fuel savings. BUT... since the stock engine makes peak torque at 1800 rpm, you'd be hard pressed to be keeping your rpm below that on the highway. Unless maybe you were just taking a nap on the shoulder? ;)

The biggest fuel mileage gain I have personally seen was with a customer years ago who drove like an old lady and was meticulous about logging his fuel fills/mileage and everything else. After a "power build" which included a compression bump, headers, intake and small 4bbl carb AND most importantly a longer duration/higher lift camshaft, he saw his highway fuel consumption for his (stock geared on stock tires FJ60) drop from 13mpg to just over 16mpg. A 25% gain!

I attribute that primarily to the change in camshaft. The factory camshaft is well beyond it's efficiency range when cruising at North American highway speeds. The camshaft bumped the efficiency range upward into a more appropriate area for how the rigs gets used here. Mr Toyoda and friends expected the old F engines to spend their lives creeping around back roads, fields and village streets in the third world, not running down multilane highways in the US. To the best of my knowledge they never changed the camshaft specs over the years. If they did it was still not enough.

To your original question... around town You will almost certainly not see any improvement. For pure highway runs if you drive gentle, just relaxing in the right hand lane, I would hopefully expect to see about 10% or so gains in the long term. In flat country. In the hills and mountains, all bets are off. If you push the rig in terms of speed/acceleration/"sportiness", you will never see any difference with the 5 speed.

Mark...
 
Last edited:
Hold on a second... Chinese Cummins???
The blocks are made and bored in China then sent to Indiana and finished machining and assembly. They install service sleeves so it is not the same 2.8 sold in the Asian market. The 4bt, 5.9 or 6.7 do not have service sleeves. The 2.8 was used in F250s in Latin America.

Check out the Ultimate Adventure videos they had several rigs powered by the R2.8 and no failures. Look up Dirt Every day video where Fred installed the R2.8 in his Tube Sock jeep and drove under water twice. Big tire garage has a square back Wagoneer with wrangler front clip that has video in Moab.
 
Last edited:
Consensus appears to be that an FJ40 is not an economy vehicle. As for cool, it’s over the top
 
My switch from 4.1 to 3.7 gears netted me about 10% increase in fuel economy. To put it another way, about 1 mpg.

A modern Chevy V8 will do “better”…but not “good”.
 
My switch from 4.1 to 3.7 gears netted me about 10% increase in fuel economy. To put it another way, about 1 mpg.

A modern Chevy V8 will do “better”…but not “good”.
16 mpg once or twice at 60 - 65 mph with fuel injected vortec 350 in front of an NV4500 and narrow 33" Toyo M-55s. 1975 4.11s

Usually 13-14, and 12 mpg in town.
 
As mentioned earlier in the responses, lugging to low while cruising will drop you below the efficiency range of the engine and eliminate an furl savings. BUT... since the stock engine makes peak torque at 1800 rpm, you'd be hard pressed to be keeping your rpm below that on the highway. Unless maybe you were just taking a nap on the shoulder? ;)

The biggest fuel mileage gain I have personally seen was years ago with a customer years ago who drove like an old lady and was meticulous about logging his fuel fills/mileage and everything else. After "power build" which included a compression bump, headers, intake and small 4bbl carb AND most importantly a longer duration/higher lift camshaft, he saw his highway fuel consumption for his (stock geared on stock tires FJ60) drop from 13mpg to just over 16mpg. A 25% gain!

I attribute that primarily to the change in camshaft. The factory camshaft is well beyond it's efficiency range when cruising at North American highway speeds. The camshaft bumped the efficiency range upward into a more appropriate area for how the rigs gets used here. Mr Toyoda and friends expected the old F engines to spend their lives creeping around backroads, fields and village streets in the third world, not running down multilane highways in the US. To the best of my knowledge they never changed the camshaft specs over the years. if they did it was still not enough.

To your original question... around town You will almost certainly not see any improvement. For pure highway runs if you drive gentle, just relaxing in the right hand lane, I would hopefully expect to see about 10% or so gains in the long term. In flat country. In the hills and mountains, all bets are off. If you push the rig in terms of speed/acceleration/"sportiness", you will never see any difference with the 5 speed.

Mark...
My son is driving it back and forth from college in Central Texas and it's quite flat. The highest thing we have here is an overpass
 
4 cyl diesel?
Dual-spark ignited gasoline 4 cylinder, Datsun / Nissan Z24 with a 32/36 Weber. Any of the efficiency that I observed is likely because I'm making more NOx, as the factory set-up used retarded spark timing to make gains with the exhaust. My O2-sensor suggests that I'm really lean when I'm running EGR, like beyond the gauge-range. I'm lazy and I run the engine with vacuum controls instead of the computer, as I can't figure out how to fix the computer-controlled carb with enrichment solenoid.

The thing that I like about my Datsun is it has a 5-speed, and it has awesome compression-braking. The 40 with 4.11s, 215/75/R15s, H42 is essentially slowing down with the brake pedal, combined with some down-shifting, but, I can really dial-in the Datsun without using friction brakes, as the brakes get hot (smoke), driving at altitude in the mountains.
 
The blocks are made and bored in China then sent to Indiana and finished machining and assembly.

Knowing what I know now, I'd go another direction. It's fine. But it wouldn't be my first choice.
 
Even diesels won’t give you much of an economy bump. They are just tractors with awful aerodynamics and like to rev low. You will never see mpg money back on a 5spd swap and for sure never on a diesel swap u less you get the stuff very very cheap.

I’ve got a 1988 BJ74, (like a “modern” FJ40) 4cyl turbo diesel, H55f and I’ve averaged 20mpg for over 5 years of tracking and 60k miles. Best almost all highway was 24mpg. That’s city/hwy winter summer etc. most of the time it’s 44-60mph and back roads. That’s 6-8mpg better than a 40 on average with the added cost of diesel.


Cheapest way to improve your mpg? Buy a Corolla 😂.
 

Users who are viewing this thread

Back
Top Bottom