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MPG vs HP Compromise

coachgeo

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Just my 2 cents,
I believe my m1078 is far from being geared correctly. Last night I tested gps speed and checked engine rpm.
2645 rpm at 61 mph, level grade. Cat recommends for the best balance of performance and fuel mileage
2000 @ 60 with a max cruuse speed of 65. Also a recommended minimum cruise speed of 55 @ 1800.
Makes me wonder if the military designed the vehicle with a top speed as a primary consideration.
The torque and horsepower drops very fast as the rpms are pushed above 2400. My 1078 is 274hp
with 3:90 gears….
I owned a Hawkins class A with a 3116 and it had plenty of power, it blocked more wind and was much heavier
than a 1078. At cruise 65mph it was only turning 1650 rpm. I pulled a 27’ enclosed trailer most of the time.
The fuel mileage was great, 9 to just over 10 mpg. I drove with the flow of traffic mostly 70 mph.
One of the local construction companies has a tri axle dump with a 3126 and regularly weigh in at
70000 lbs when moving there excavator from job to job. He did say it a turd with that kind of load
but it will pull it to road speed.View attachment 890541View attachment 890542View attachment 890543
Bingo you are correct (sorta) - these trucks were geared correctly..... for their military task...... which is NOT correct for our commercial or camper task as your examples show very well.
 

Awesomeness

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Just my 2 cents,
I believe my m1078 is far from being geared correctly.
It's not like they didn't have access to this information when they designed it. They geared it exactly how they wanted it geared, for their specs/needs. If it's "far from being geared correctly" for your needs, change it, but you didn't discover some mistake or anything.
 

Mullaney

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Just my 2 cents,
I believe my m1078 is far from being geared correctly. Last night I tested gps speed and checked engine rpm.
2645 rpm at 61 mph, level grade. Cat recommends for the best balance of performance and fuel mileage
2000 @ 60 with a max cruuse speed of 65. Also a recommended minimum cruise speed of 55 @ 1800.
Makes me wonder if the military designed the vehicle with a top speed as a primary consideration.
The torque and horsepower drops very fast as the rpms are pushed above 2400. My 1078 is 274hp
with 3:90 gears….
I owned a Hawkins class A with a 3116 and it had plenty of power, it blocked more wind and was much heavier
than a 1078. At cruise 65mph it was only turning 1650 rpm. I pulled a 27’ enclosed trailer most of the time.
The fuel mileage was great, 9 to just over 10 mpg. I drove with the flow of traffic mostly 70 mph.
One of the local construction companies has a tri axle dump with a 3126 and regularly weigh in at
70000 lbs when moving there excavator from job to job. He did say it a turd with that kind of load
but it will pull it to road speed.View attachment 890541View attachment 890542View attachment 890543
.
Gotta remember that this "Woke" crap has been around a long time. It just wasn't called that back then... Regulating speed was a consideration when these trucks were built. Private Snuffy could only go so fast as long as he was regulated.

An awful lot like "back in the day" when Carolina Freight had their tractors governed to 55 when our peanut farmer president was regulating speed to save gas (fuel). The drivers and mechanics called them "Yellow Dot" trucks when regulated that way (spot of yellow paint).

The military regulated with gears though because Private Snuffy would figure out a way to bypass a roadspeed governor...
.
 

chucky

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Now this will get me beat down but I AINT SKEEERD ! SO it is what it is
A. For the exception of a small few on this forum we dont use these trucks for hire theyre our hobby / were not on a timeline and if your honest we dont put any miles to speak of on these trucks that would make a rabbits dam about fuel mileage in the big picture and if so just keep your foot out of it and dont drive it like a fire truck !
B. If you stay off the interstate most all of this becomes a mute point ! I get the hwy gears to drop rpms thats great! If were quibleing over fuel cost the money spent on hwy gears will never be recooped anyways in fuel savings and the part that most seem to forget with these trucks is the mfg of these tires say/said 55mph tops so in my hillbilly logic computes to stay under 55 so stay off the interstate cause you are in the way and end of the day we are dangerous at those speeds and 99 percent of you have never blown a steer tire at 70 wth 80.000 lbs behind you and especially back when power steering wast on most big trucks ! Its an awful feeling to maybe have a bus load of kids beside you when she blows NOW how are you gona bring all this truck to a stop without killing someone ! Cause you wanted to go 60 65 70 when youve been warned these tires arnt made to turn this fast ! Your grand children will still be feeling the effects of the lawsuits against you long after your gone !
C. Get on the skinny roads thats where the treasures are ! 2 and a half million miles i was always in a rush or make an appointment and so wanted to have time to stop and look and scrounge thru all the treats sprinkled all over the country on the little roads and little towns you never herd of maybe in your own backyard ! Every exit on the interstate look the same have the same 10 major names within a half mile and its all ugly as sin itself ! ENJOY YOUR HARD WORK YOUVE PUT INTO YOUR TRUCKS let them be what they were designed to be for the most part and slow down ! Your missing all the good stuff !
 

Mullaney

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Now this will get me beat down but I AINT SKEEERD ! SO it is what it is
A. For the exception of a small few on this forum we dont use these trucks for hire theyre our hobby / were not on a timeline and if your honest we dont put any miles to speak of on these trucks that would make a rabbits dam about fuel mileage in the big picture and if so just keep your foot out of it and dont drive it like a fire truck !
B. If you stay off the interstate most all of this becomes a mute point ! I get the hwy gears to drop rpms thats great! If were quibleing over fuel cost the money spent on hwy gears will never be recooped anyways in fuel savings and the part that most seem to forget with these trucks is the mfg of these tires say/said 55mph tops so in my hillbilly logic computes to stay under 55 so stay off the interstate cause you are in the way and end of the day we are dangerous at those speeds and 99 percent of you have never blown a steer tire at 70 wth 80.000 lbs behind you and especially back when power steering wast on most big trucks ! Its an awful feeling to maybe have a bus load of kids beside you when she blows NOW how are you gona bring all this truck to a stop without killing someone ! Cause you wanted to go 60 65 70 when youve been warned these tires arnt made to turn this fast ! Your grand children will still be feeling the effects of the lawsuits against you long after your gone !
C. Get on the skinny roads thats where the treasures are ! 2 and a half million miles i was always in a rush or make an appointment and so wanted to have time to stop and look and scrounge thru all the treats sprinkled all over the country on the little roads and little towns you never herd of maybe in your own backyard ! Every exit on the interstate look the same have the same 10 major names within a half mile and its all ugly as sin itself ! ENJOY YOUR HARD WORK YOUVE PUT INTO YOUR TRUCKS let them be what they were designed to be for the most part and slow down ! Your missing all the good stuff !
.
Well said!
A lot of truth in those few words too...

.
 

Xengineguy

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It's not like they didn't have access to this information when they designed it. They geared it exactly how they wanted it geared, for their specs/needs. If it's "far from being geared correctly" for your needs, change it, but you didn't discover some mistake or anything.
I didn’t say it was a mistake or am I claiming a new discovery…. Yes I am changing mine. Not 3:07 gears. Will report the good or bad.
Should be done in a week or so.. Wouldn’t it be nice to cruise 60/65 mph @ 1500/1650 rpm?? So much less noise and heat and fuel.
.
Gotta remember that this "Woke" crap has been around a long time. It just wasn't called that back then... Regulating speed was a consideration when these trucks were built. Private Snuffy could only go so fast as long as he was regulated.

An awful lot like "back in the day" when Carolina Freight had their tractors governed to 55 when our peanut farmer president was regulating speed to save gas (fuel). The drivers and mechanics called them "Yellow Dot" trucks when regulated that way (spot of yellow paint).

The military regulated with gears though because Private Snuffy would figure out a way to bypass a roadspeed governor...
.
 

Mullaney

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I didn’t say it was a mistake or am I claiming a new discovery…. Yes I am changing mine. Not 3:07 gears. Will report the good or bad.
Should be done in a week or so.. Wouldn’t it be nice to cruise 60/65 mph @ 1500/1650 rpm?? So much less noise and heat and fuel.
.
Best to you on your gearing change.

I would like to offer up the idea of balancing your driveshafts if you haven't already done that. You have to remove them to re-gear, so now is a prime time to do that job. And maybe replacing the universal joints as well since they will be spinning faster than ever before.
 

chucky

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It seems like a lot of that rant is predicated on the line above, but it's not correct. The Michelins are rated low, but the Goodyears are either 68MPH or 81MPH, depending on the load range you get.
View attachment 890567
RANT !!! LMAO thats funny coming from you ! I like many many others in here run MICHELIN tires on their trucks and their website plainly state MAX speed on 395s to be 55mph so how is that not correct ? A little common sence has to slip between the cracks ever once in a while GOODYEAR also make a Y rated tire for the Corvette rated at 186 mph so by your interpitation does that mean everyone with y rated tires should drive at 186 mph cause GOODYEAR says so ! Call it a rant if you want but if it sinks into 1 head i would do this every day ! As far as the hwy gears i dont have a problem at all with them at all if the owners use some common sense with the higher speeds because didnt you just have to move from colorado that outlawed military surplus veh off the road ????? You just let some of these MODIFIED trucks wind up killing some folks our ability to travel on the roads will be over ! Cause we wanted to go faster !!!0309719D-1A28-44D4-8586-39C2EA022EF6.jpeg38088E8E-427C-414F-8161-0833172FA3D4.jpeg
 

Awesomeness

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RANT !!! LMAO thats funny coming from you ! I like many many others in here run MICHELIN tires on their trucks and their website plainly state MAX speed on 395s to be 55mph so how is that not correct ? A little common sence has to slip between the cracks ever once in a while GOODYEAR also make a Y rated tire for the Corvette rated at 186 mph so by your interpitation does that mean everyone with y rated tires should drive at 186 mph cause GOODYEAR says so ! Call it a rant if you want but if it sinks into 1 head i would do this every day ! As far as the hwy gears i dont have a problem at all with them at all if the owners use some common sense with the higher speeds because didnt you just have to move from colorado that outlawed military surplus veh off the road ????? You just let some of these MODIFIED trucks wind up killing some folks our ability to travel on the roads will be over ! Cause we wanted to go faster !!!View attachment 890586View attachment 890587
You're arguing that nobody intended these trucks to go that fast, and they aren't rated to, so it isn't safe, but some versions were explicitly designed to go that fast, and had tires to do it safely. I conceded that the Michelins were rated low in my previous post, so I'm not sure why you're swooping back in like you're proving something with the picture above. All you have to do is switch to the Goodyears when you regear the axles and you've mitigated the problem. The 3:07:1 gears are out of MRAPs, so the MRAPs (which are just an FMTV with a different, even heavier body) will go that speed too.

If you want to see the ratings for all of the tires, several years ago this chart was online.
TireComparisonChart.png
 

Xengineguy

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.
Best to you on your gearing change.

I would like to offer up the idea of balancing your driveshafts if you haven't already done that. You have to remove them to re-gear, so now is a prime time to do that job. And maybe replacing the universal joints as well since they will be spinning faster than ever before.
I’m Confused?? I don’t disagree that balancing a driveline is a good idea. However, why would my driveshafts be going faster???
When you re-gear the engine and driveline slows down for the same road speed….
 

Mullaney

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I’m Confused?? I don’t disagree that balancing a driveline is a good idea. However, why would my driveshafts be going faster???
When you re-gear the engine and driveline slows down for the same road speed….
.
Just my assumption.
Figuring higher speed - depending on how fast and the gear ratio.
I haven't done the math on that.
.
 

Awesomeness

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Yes the 3.07 swap lowers the engine, trans and driveshaft RPM for a given highway speed.
Not disagreeing with this, however, one thing that is overlooked is that it's not just as simple as that. People need to look at the transmission shift points, and what speed ranges are for each gear. Now that I run the 3.07:1 gears, I find that my LMTV cruises nicely at 65MPH on the highway (low RPM in 7th gear), but is frustratingly screaming at 45 and 55MPH (it's high RPM, just before the shift point) on common roads.

Not the "slam dunk" it seems to be on paper. It just moves the problem around.
 

98G

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Not disagreeing with this, however, one thing that is overlooked is that it's not just as simple as that. People need to look at the transmission shift points, and what speed ranges are for each gear. Now that I run the 3.07:1 gears, I find that my LMTV cruises nicely at 65MPH on the highway (low RPM in 7th gear), but is frustratingly screaming at 45 and 55MPH (it's high RPM, just before the shift point) on common roads.

Not the "slam dunk" it seems to be on paper. It just moves the problem around.
I have a similar experience with my M925. Changing the tire size changed the effective final drive ratio to the point that I need to control upshifts and downshifts manually. I only see 5th gear on the interstate.
 

98G

Former SSG
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AZ/KS/MO/OK/NM/NE, varies by the day...
Not disagreeing with this, however, one thing that is overlooked is that it's not just as simple as that. People need to look at the transmission shift points, and what speed ranges are for each gear. Now that I run the 3.07:1 gears, I find that my LMTV cruises nicely at 65MPH on the highway (low RPM in 7th gear), but is frustratingly screaming at 45 and 55MPH (it's high RPM, just before the shift point) on common roads.

Not the "slam dunk" it seems to be on paper. It just moves the problem around.
I have a similar experience with my M925. Changing the tire size changed the effective final drive ratio to the point that I need to control upshifts and downshifts manually. I only see 5th gear on the interstate.
 

Ronmar

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It would be nice to be able to reprogram the shift points, or manually upshift on the Allison. Awesomeness, have you ever checked/calibrated your TPS?
 

Awesomeness

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It would be nice to be able to reprogram the shift points, or manually upshift on the Allison. Awesomeness, have you ever checked/calibrated your TPS?
Yeah, I've recalibrated it. Even got a new Throttle Position Sensor. Mine is one of the harder-shifting trucks, which only makes the shifting more annoying.
 

Elijah95

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I’ve got a 7 ton MTVR, and drove it home across the nation from Cali to Georgia wide open with a M989 Hemat trailer in tow with a Gama Goat on the deck averaging 2-3mpg in town and 5.7mpg banging on the governor 65mph/2120rpm

Factory the truck was tuned to 370/425horse with the latter putting out 1550 torque, also known as a “multitorque tune” marketed by cat, able to switch back and forth via weight selection on the CTIS controller reserving high output for anything beyond 0-2 ton cargo selection. I was stuck in the 0-2 mode due to a ECM issue.

Nowadays, I’ve retuned the truck with a custom written file by a well known caterpillar tune author, and with supporting mods I’m around 570 horse and 1800 torque coming in at 32,000ibs. Driving the truck full tilt, I’m averaging 5.3mpg highway and still 2-3 around town, however economizing I can eek out nearly 7.5mpg at 50mph. I can’t bear to go any slower, but peak economy comes in at 43mph in my truck. The Allison 7 speed transmission is a double overdrive, but the 1.36 under drive transfer case and geared hubs severely handicap highway economy.

The single greatest tool to increase fuel efficiency is a pyrometer and boost gauge, for any given speed if you’ll back your throttle down to get EGT and boost as low as humanly possible to barely maintain speed will save you substantially in fuel because less fuel=less exhaust gas temp


Sent from my iPhone using Tapatalk
 

Ronmar

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Yeah, I've recalibrated it. Even got a new Throttle Position Sensor. Mine is one of the harder-shifting trucks, which only makes the shifting more annoying.
Yours is a WTEC2, i have seen some screenshots of the trans controller programming, and it appears that auxiliary hold was possibly enabled on non winch trucks as a default auxiliary input function(Wire 153 to signal ground 161B). When enabled this overrides the normal shift parameters and holds the trans in its current gear. you would still need to get it into 7th gear, but once there it would hold it there as you backed off to the lower cruise speed…
 
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