gear ratio query
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5th Wheeling
Joined: Nov 2012
Posts: 35
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gear ratio query
I am building a 78 F150. It is a work truck ( not a race truck) I am confused about how to determine the correct third member ratio.
rear tyre size ; 235/70/15 giving a diameter of 27.95" I'm using a stock FE360 motor. I would like to pull the hill with a load at a reasonable speed. So ....... what would be a good ratio for hi end torque without tacking out my motor? and still be able to chug around on the dirt roads where most of my jobs are? I al also thinking about a posi read spool again, not for speed but rather so when it gets soupy on the dirt roads I'm paddling with both rear tyers and not just one with the standard rear end. any input appreciated.
rear tyre size ; 235/70/15 giving a diameter of 27.95" I'm using a stock FE360 motor. I would like to pull the hill with a load at a reasonable speed. So ....... what would be a good ratio for hi end torque without tacking out my motor? and still be able to chug around on the dirt roads where most of my jobs are? I al also thinking about a posi read spool again, not for speed but rather so when it gets soupy on the dirt roads I'm paddling with both rear tyers and not just one with the standard rear end. any input appreciated.
Lead Driver
Joined: Oct 2018
Posts: 7,862
Likes: 2,359
As with everything it's always about trade offs. there is no perfect all around gearing unless you have an overdrive.
Since you don't you have to look at what you do most. you don't have much power so there's that, you say you want to pull a hill at reasonable speed, what transmission do you have and how heavy? would you rather pull it in a lowwr gear so you can get better MPG the rest of the time? or do you want a better towing set up screaming down the road at 3000 rpm ?
My opinion is whatever gears you have are the right ones. just deal with it the factory already made the compromises for you. assuming you have stock gear still.
Since you don't you have to look at what you do most. you don't have much power so there's that, you say you want to pull a hill at reasonable speed, what transmission do you have and how heavy? would you rather pull it in a lowwr gear so you can get better MPG the rest of the time? or do you want a better towing set up screaming down the road at 3000 rpm ?
My opinion is whatever gears you have are the right ones. just deal with it the factory already made the compromises for you. assuming you have stock gear still.
Fleet Mechanic
Joined: Feb 2004
Posts: 1,508
Likes: 332
From: Arlington,Wa
78 F150 and a stock FE360?? Was that swapped in? Should have a 351M. To which in my opinion, would be a step up and can be slightly modded to get a bit more oomph out of it. At least enough to accomplish what you're doing anyway. If your not sure of what what engine you have ...snap a pic and post it here.
Lead Driver
Joined: Oct 2018
Posts: 7,862
Likes: 2,359
360,351,400, they're all gutless so the gearing should be the same.
These pickups did their job in the day and they did it well. but if you're wanting to use one today as a daily driver or work rig you simply have to accept the limitations and the fuel economy . your best effort and massive amounts of money invested won't give you a vehicle as good as a $5000 pickup made in the 90's. people really need to think about what their end game is and how much they really want it before they get too deep.
I say run the gears you have there is no magic bullet you have to compromise. the engineers were well aware of this when they built it.
These pickups did their job in the day and they did it well. but if you're wanting to use one today as a daily driver or work rig you simply have to accept the limitations and the fuel economy . your best effort and massive amounts of money invested won't give you a vehicle as good as a $5000 pickup made in the 90's. people really need to think about what their end game is and how much they really want it before they get too deep.
I say run the gears you have there is no magic bullet you have to compromise. the engineers were well aware of this when they built it.
Fleet Mechanic
Joined: Feb 2022
Posts: 1,370
Likes: 706
If you proceed with the swap, here's a good calculator to tell you the engine speed you'll be turning.
https://spicerparts.com/calculators/...rpm-calculator
https://spicerparts.com/calculators/...rpm-calculator
Hotshot
Joined: Feb 2004
Posts: 10,785
Likes: 2,595
From: The Shenandoah Valley
I am building a 78 F150. It is a work truck ( not a race truck) I am confused about how to determine the correct third member ratio.
rear tyre size ; 235/70/15 giving a diameter of 27.95" I'm using a stock FE360 motor. I would like to pull the hill with a load at a reasonable speed. So ....... what would be a good ratio for hi end torque without tacking out my motor? and still be able to chug around on the dirt roads where most of my jobs are? I al also thinking about a posi read spool again, not for speed but rather so when it gets soupy on the dirt roads I'm paddling with both rear tyers and not just one with the standard rear end. any input appreciated.
rear tyre size ; 235/70/15 giving a diameter of 27.95" I'm using a stock FE360 motor. I would like to pull the hill with a load at a reasonable speed. So ....... what would be a good ratio for hi end torque without tacking out my motor? and still be able to chug around on the dirt roads where most of my jobs are? I al also thinking about a posi read spool again, not for speed but rather so when it gets soupy on the dirt roads I'm paddling with both rear tyers and not just one with the standard rear end. any input appreciated.
I have used 4wd in lo without front hubs engaged just for a slow pull.
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5th Wheeling
Joined: Nov 2012
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Friends,
lots of good feedback. I have not opened the rear as of yet to count splines and find out what is in there now. it is 2wd that is why i am wanting a posi rear to help in the mud. the trailer I pull is a service bed truck trailer with a 10k generator on the tongue. I do off grid construction and have ladders and saws and the like... probably 2500lb or less, never really weighed it.. would like to keep it at 50ish going up hills on hardtop.
I do have a yard full of these older ford trucks; I have always loved the twin I-beam front end(less moving parts) I have;
1969 F-350 dually with factory 10'flatbed fe 390
1971 F-100 fe360
1978 F-150 super cab 351w but changing to fe361
1978 F-250 (son's truck) 351M
1979 F-600 with 1000gal. water tank 370
I would like to thank everyone for all there input you are a collective wealth of knowledge and experience.
lots of good feedback. I have not opened the rear as of yet to count splines and find out what is in there now. it is 2wd that is why i am wanting a posi rear to help in the mud. the trailer I pull is a service bed truck trailer with a 10k generator on the tongue. I do off grid construction and have ladders and saws and the like... probably 2500lb or less, never really weighed it.. would like to keep it at 50ish going up hills on hardtop.
I do have a yard full of these older ford trucks; I have always loved the twin I-beam front end(less moving parts) I have;
1969 F-350 dually with factory 10'flatbed fe 390
1971 F-100 fe360
1978 F-150 super cab 351w but changing to fe361
1978 F-250 (son's truck) 351M
1979 F-600 with 1000gal. water tank 370
I would like to thank everyone for all there input you are a collective wealth of knowledge and experience.
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5th Wheeling
Joined: Nov 2012
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it started with a 300 il6 I put the 351w from an 85 bronco into it and remain unimpressed with the performance. seems that the 71' with the 360 has more pull to it.i got a 361 that the book says has more torque to it so that is my motivation for yet another swap.
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