how much of a difference will you see?
MPG difference with 2F engine between 4 speed and h55f 5 speed (1 Viewer)
- Thread starter cvan1971man
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Unfortunately I don’t think you will see much or any at all. It depends I guess on your tire size and what kind of driving you do interstate vs around town. Maybe for long trips when you are in 5th gear for long periods of time you might see something. I’m only driving around town with very little interstate driving so 5th would pretty much be useless for me. I’m on 31” tires and stock gearing. Maybe 33” one day. I kinda gave up on mpg a long time ago and just enjoy the truck for what it is. It’s about smiles per gallon right!
Jason
Jason
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You will have to drive like grandma to see a gain. And then it begets the question of whether you would have got the same result just driving the four speed in eco mode?
If you lug the engine below optimum torque, then you’re losing efficiency. And if you try to drive fast enough with an overdrive to reach optimum torque, the increased wind resistance against the vertical wall of a 40 windshield kills mpg.
I wrote an article in Toyota Trails about this almost twenty years ago.
If you lug the engine below optimum torque, then you’re losing efficiency. And if you try to drive fast enough with an overdrive to reach optimum torque, the increased wind resistance against the vertical wall of a 40 windshield kills mpg.
I wrote an article in Toyota Trails about this almost twenty years ago.
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Changes, such as overdrive, 3.7-pinon ring gear changes, that puts the rpm on the chopping block. H55 isn't a stand-alone mod.
I'm not sure that we have solid baseline data on the 2F FJ40 for mpg. The smiles-per-mile is just wishful thinking. Mudders install fuel cells, hacking up the truck just to not carry a Jerry can for added range. MPH, MPG how long until the truck or driver needs a break? I measure mpg to determine the tune of the engine, as part of its preservation and maintenance. A lean-running carb can't be good for power-output or longevity of the engine.
With a static compression ratio of 7.8:1, the 2F isn't burning fuel like the higher compression ratios of modern engines. Perhaps the combustion cycle is best performed within a narrower-range of rpm than an engine with higher compression, variable valve timing, etc.? The long-stroke of the 2F means that there is more parasitic loss of energy by recripricating engine parts, like rods and pistons.
I'm not sure that we have solid baseline data on the 2F FJ40 for mpg. The smiles-per-mile is just wishful thinking. Mudders install fuel cells, hacking up the truck just to not carry a Jerry can for added range. MPH, MPG how long until the truck or driver needs a break? I measure mpg to determine the tune of the engine, as part of its preservation and maintenance. A lean-running carb can't be good for power-output or longevity of the engine.
With a static compression ratio of 7.8:1, the 2F isn't burning fuel like the higher compression ratios of modern engines. Perhaps the combustion cycle is best performed within a narrower-range of rpm than an engine with higher compression, variable valve timing, etc.? The long-stroke of the 2F means that there is more parasitic loss of energy by recripricating engine parts, like rods and pistons.
I had consider this mod… @wngrog gave me the best advice I could find. It’s a bigger modification to the tunnel cover and my best option in his thinking was to swap the 4.11 gears in the diff to 3.70. I have acquired these differentials and will be making that swap this summer.
It should have been finished by now but an option popped up for another project that took 6 months to finish so I’ll document the before and after stats when it gets completed. Hoping to start early April ‘25
It should have been finished by now but an option popped up for another project that took 6 months to finish so I’ll document the before and after stats when it gets completed. Hoping to start early April ‘25
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- #8
I’m not expecting a huge change beyond dropping the cruising rpm a few points. Currently at 60mph I think it’s around 2900-3000 rpm. Honestly, my 1974 FJ40 was a highway ride when I was living near the Canada border in Vermont and would make frequent trips to New Jersey and Delaware. This 9-11 hour one-way rides were fun but I was 21… 50 years later I no longer have that “Goggles Paisano” (1) driving mentality.
I am a mellowed driver now, my Land Cruiser is in spectacular condition and I enjoy working on it. I take it off-road (so to speak) but only on a few dry dirt trails, and my own dirt driveway. I am not wheeling it through rocky crevasses or washed out creek beds. so this mod just seemed like the next link in the chain.
I will document the data so keep an eye open later on…I have a gps iPhone speedometer and the tachometer on the Holley Sniper handheld. I’ll photograph all of it for you
(1) Goggles Paisano was a Fred Flintstone character. I am old enough to have seen the original episode.
flintstones.fandom.com
I am a mellowed driver now, my Land Cruiser is in spectacular condition and I enjoy working on it. I take it off-road (so to speak) but only on a few dry dirt trails, and my own dirt driveway. I am not wheeling it through rocky crevasses or washed out creek beds. so this mod just seemed like the next link in the chain.
I will document the data so keep an eye open later on…I have a gps iPhone speedometer and the tachometer on the Holley Sniper handheld. I’ll photograph all of it for you
(1) Goggles Paisano was a Fred Flintstone character. I am old enough to have seen the original episode.
Indianrockolis 500
"Indianrockolis 500" is the thirteenth episode of the fifth season of the original series, The Flintstones. It aired on December 10, 1964. Fred hopes to win an auto race to pay for the kids' higher education, but he's having all sorts of problems with the racing car that Barney built. Barney's...
1911
chupacabra
I am running (stock for my year) 3.70 diffs, 33" tires, and an H41 transmission (same 1:1 4th gear as the stock H42). It gets 11-13 mpg combined local & highway driving. One tank on a long trip, going a fairly steady 65 mph with a consistent tailwind, I got 14 mpg.
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- #11
Wow, I was hoping for better. This is my son's daily driver. He gets about 13-14 doing 65. Doing 75 he gets 11-12.I am running (stock for my year) 3.70 diffs, 33" tires, and an H41 transmission (same 1:1 4th gear as the stock H42). It gets 11-13 mpg combined local & highway driving. One tank on a long trip, going a fairly steady 65 mph with a consistent tailwind, I got 14 mpg.
I honestly don't know what diffs are in our FJ. It is a 1973 body, but 78 2f, tranny and tcase
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- #12
Jason,
Wow, I would have thought that with as high as the engine is revving with the 4 speed at 65 MPH, by adding a taller gear in the 5 speed, there would be a huge rpm reduction, thereby increasing fuel efficiency.
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- #13
what other reasons?
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- #14
that is crazy - I would have thought that with as high as the engine is revving with the 4 speed at 65 MPH, by adding a taller gear in the 5 speed, there would be a huge rpm reduction, thereby increasing fuel efficiency.
1911
chupacabra
3.70 diffs came with U.S.-market 40's beginning in 1979, so yours are probably 4.11.
"Avoid excessively high speeds. The difference between 50 mph and 70 mph may save 15 to 20 percent on your fuel bill." - 1975 Land Cruiser Owner's Manual.
I get as much as 14 or 15-mpg with 2F, 4.11s, and 215/75/R15 during summer. It was on a switchback highway up and down the mountain (35-mph max speed posted). A non-USA OEM 2F carb that I installed scored about one-mpg more than the richer-jetted OEM '75 Aisan. If I had the 2F-EGR hooked up it would probably buy an mpg or so? My other rig was specified as 28-highway EPA-estimates, but, I did as much as 33, with a partial emissions delete. This is at 7,000-ft. plus - your location is more efficient for internal combustion engines.
I get as much as 14 or 15-mpg with 2F, 4.11s, and 215/75/R15 during summer. It was on a switchback highway up and down the mountain (35-mph max speed posted). A non-USA OEM 2F carb that I installed scored about one-mpg more than the richer-jetted OEM '75 Aisan. If I had the 2F-EGR hooked up it would probably buy an mpg or so? My other rig was specified as 28-highway EPA-estimates, but, I did as much as 33, with a partial emissions delete. This is at 7,000-ft. plus - your location is more efficient for internal combustion engines.
1911
chupacabra
I think you are overestimating the overdrive 5th gear in the H55, it's a modest reduction - 0.85:1, i.e. only 15% higher than 4th gear.
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- #18
THanks for educating me!
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- #19
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?
POPO AGIE
SILVER Star
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.
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.
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