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 > Ford super duty 3.31 rear end. Will it be a big mistake. ?

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4x4ord

Alberta

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Posted: 01/30/21 08:53am Link  |  Quote  |  Print  |  Notify Moderator

The standard tires on the higher trim trucks are 34” diameter. I can’t imagine a situation where 3.55 gears would be nicer to have pulling a 16000 lb rv vs 3.31 gears. When do you think you would notice an advantage?


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4x4ord

Alberta

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Posted: 01/30/21 10:15am Link  |  Quote  |  Print  |  Notify Moderator

Lantley wrote:

I 'll take slightly better over slightly worse every time.
I'm not sure why some feel the need to go through a lot of mumbo jumbo and tech speak to reach the slightly better conclusion.
The higher ratio will always tow better.
3.31 and 3.55 are pretty close to start with but the higher ratio still performs better when towing. Calculating a performance standard that uses 30" tires is misguided and misleading. Very few are towing RV's with 30+" tires


Consider this: To get your trailer moving your current truck starts out in 1st gear and with 3.73 rear gears the 910 lbft of engine torque is multiplied:

3.73 x 3.094 = 11.54 times giving you potentially 910 x 11.54 = 10,500 lbft to the rear wheels.

The torque to the rear wheels of the new Ford with its ten speed transmission and a 3.31 rear end looks something like this
3.31 x 4.615 = 15.28 which could potentially put 15.28 x 1050 = 16,044 lbft of torque to the rear axle.

To get 16,044 lbft of torque to the rear axle of your 2019 GM you would need a 5.70:1 rear end.

My point is that 3.31 gears with a ten speed is far more than slightly better than what you are used to. When we are only pulling 16,000 to 18,000 lb rvs 16,000 lbft of torque is tremendous. Having 10 gears to choose from is really kind of over kill while pulling loads that the SRW trucks are capable of. Realize that 9th with 3.31 final drive is near identical to 10th with 3.55 gears. So the 3.31 equipped truck has tremendous capability to get our relatively light trailers moving in 1st gear, has more than enough gears to keep the engine at it's peak operating range while towing heavy or in the hills and has a 10th gear that can be utilized for optimum fuel economy when towing on flat ground or not towing. People are free to choose a 3.55 gear ratio for their SRW diesel and they will be happy but they are giving up a little economy to gain nothing.

StirCrazy

Kamloops, BC, Canada

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Posted: 01/30/21 10:39am Link  |  Quote  |  Print  |  Notify Moderator

blofgren wrote:



If you Ford guys towed with a Cummins you would be absolutely amazed.....I usually have to give my truck some throttle when descending BC passes when pulling my 16k fiver loaded for a 3 week trip. And no cruise control or automatic braking of the service brakes.


but then we would be seen in a Dodge [emoticon] when I bought my 2014 (in 2016) I tried out all the big three, dodge was actoula on the bottom of my list. rode rouch, and felt very enimic driving around town. I am sure it pulls like a freight train but it just wasnt a fun or nice driving experiance to me.

the biggest thing is the fords never had an "exhaust brake" untill the 2015 model, before then it was just using the VV turbo which works but not near as good as a real exhaust brake. My VVT will hold 14000lbs of 5th wheel going down the coq and I only have to tap the brakes two or three times at the big hill before the tunnels traveling from kamloops to van. my buddy has a 2017 and a bit heavier of a trailer and he sets his cruise and doesnt touch his brakes all the way unless trafic is slower.

Steve


2014 F350 6.7 Platinum
2016 Cougar 330RBK

cummins2014

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Posted: 01/30/21 12:35pm Link  |  Quote  |  Print  |  Notify Moderator

StirCrazy wrote:

blofgren wrote:



If you Ford guys towed with a Cummins you would be absolutely amazed.....I usually have to give my truck some throttle when descending BC passes when pulling my 16k fiver loaded for a 3 week trip. And no cruise control or automatic braking of the service brakes.


but then we would be seen in a Dodge [emoticon] when I bought my 2014 (in 2016) I tried out all the big three, dodge was actoula on the bottom of my list. rode rouch, and felt very enimic driving around town. I am sure it pulls like a freight train but it just wasnt a fun or nice driving experiance to me.

the biggest thing is the fords never had an "exhaust brake" untill the 2015 model, before then it was just using the VV turbo which works but not near as good as a real exhaust brake. My VVT will hold 14000lbs of 5th wheel going down the coq and I only have to tap the brakes two or three times at the big hill before the tunnels traveling from kamloops to van. my buddy has a 2017 and a bit heavier of a trailer and he sets his cruise and doesnt touch his brakes all the way unless trafic is slower.

Steve



There is no tapping brakes with a Cummins , and I am towing the same weight . I spend nearly 16 years in a Ford Superduty, I know all about them ,they are okay, they got nothing on the Cummins .

4x4ord

Alberta

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Posted: 01/30/21 12:45pm Link  |  Quote  |  Print  |  Notify Moderator

^^^^Somehow we need to communicate to our trucks so that the engine brake will only brake the necessary amount. How do you communicate your wishes to the Cummins exhaust brake?

Lantley

Ellicott City, Maryland

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Posted: 01/30/21 02:26pm Link  |  Quote  |  Print  |  Notify Moderator

4x4ord wrote:

Lantley wrote:

I 'll take slightly better over slightly worse every time.
I'm not sure why some feel the need to go through a lot of mumbo jumbo and tech speak to reach the slightly better conclusion.
The higher ratio will always tow better.
3.31 and 3.55 are pretty close to start with but the higher ratio still performs better when towing. Calculating a performance standard that uses 30" tires is misguided and misleading. Very few are towing RV's with 30+" tires


Consider this: To get your trailer moving your current truck starts out in 1st gear and with 3.73 rear gears the 910 lbft of engine torque is multiplied:

3.73 x 3.094 = 11.54 times giving you potentially 910 x 11.54 = 10,500 lbft to the rear wheels.

The torque to the rear wheels of the new Ford with its ten speed transmission and a 3.31 rear end looks something like this
3.31 x 4.615 = 15.28 which could potentially put 15.28 x 1050 = 16,044 lbft of torque to the rear axle.

To get 16,044 lbft of torque to the rear axle of your 2019 GM you would need a 5.70:1 rear end.

My point is that 3.31 gears with a ten speed is far more than slightly better than what you are used to. When we are only pulling 16,000 to 18,000 lb rvs 16,000 lbft of torque is tremendous. Having 10 gears to choose from is really kind of over kill while pulling loads that the SRW trucks are capable of. Realize that 9th with 3.31 final drive is near identical to 10th with 3.55 gears. So the 3.31 equipped truck has tremendous capability to get our relatively light trailers moving in 1st gear, has more than enough gears to keep the engine at it's peak operating range while towing heavy or in the hills and has a 10th gear that can be utilized for optimum fuel economy when towing on flat ground or not towing. People are free to choose a 3.55 gear ratio for their SRW diesel and they will be happy but they are giving up a little economy to gain nothing.

You may have a point in terms of getting things rolling. There were a few Dodge guys complaining their Cummins were a bit lacking when it came to getting started a few few years ago. Maybe 2014 model years, I not that familiar with Ram trucks.
But overall I'm less concerned about getting things rolling vs. climbing the grade.
I never wished I had pulled away from that light faster, But I will always want more power climbing the grade.


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Lynnmor

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Posted: 01/30/21 03:13pm Link  |  Quote  |  Print  |  Notify Moderator

cummins2014 wrote:



There is no tapping brakes with a Cummins , and I am towing the same weight . I spend nearly 16 years in a Ford Superduty, I know all about them ,they are okay, they got nothing on the Cummins .


Perhaps you never owned a 6.7 Ford diesel or didn't drive one enough to appreciate how they work. Since my rear tires wear faster than the front now, I don't want a pair of tires doing even more work. Yes, I know you have more tires than me. Would sliding the rear tires to slow down satisfy your need for considerable exhaust braking?





cummins2014

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Posted: 01/30/21 03:20pm Link  |  Quote  |  Print  |  Notify Moderator

4x4ord wrote:

^^^^Somehow we need to communicate to our trucks so that the engine brake will only brake the necessary amount. How do you communicate your wishes to the Cummins exhaust brake?


For me cruise control works the best , on steep grades I set it usually for 5 mph less then I want to go it gains that much before it holds . Gradual grade whatever speed I want to go . I find with the Cummins even on steep grades it works too well just letting off the pedal .

* This post was edited 01/30/21 03:37pm by cummins2014 *

cummins2014

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Posted: 01/30/21 03:36pm Link  |  Quote  |  Print  |  Notify Moderator

Lynnmor wrote:

cummins2014 wrote:



There is no tapping brakes with a Cummins , and I am towing the same weight . I spend nearly 16 years in a Ford Superduty, I know all about them ,they are okay, they got nothing on the Cummins .


Perhaps you never owned a 6.7 Ford diesel or didn't drive one enough to appreciate how they work. Since my rear tires wear faster than the front now, I don't want a pair of tires doing even more work. Yes, I know you have more tires than me. Would sliding the rear tires to slow down satisfy your need for considerable exhaust braking?


You lost me on whatever you are trying to say . I only have four tires . My comment was simple the Cummins is second to none as far as how well the exhaust brake works, if the Ford now works as well , that’s great . As far as the Fords go there was a day the exhaust brake on their Powerstroke was non existent, I’m sure they have improved .

4x4ord

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Posted: 01/30/21 03:36pm Link  |  Quote  |  Print  |  Notify Moderator

^^^^^ If you need more torque climbing a grade the transmission will drop a gear. Say you are pulling in some hilly terrain. With the 3.31 equipped truck you might feel 10 gears is too many so you lock out tenth. Now the 3.31 is in ninth running almost identical rpms to the 3.55 equipped truck. You come to a hill and both trucks require full throttle. Both trucks are going to drop a gear at the same time. At 60 mph the 3.55 will drop to ninth and the engine will be at 1446 rpm. The 3.31 will drop to 8th and be running at 1668 rpm. If pulling the hill requires more mower than the engine can deliver at 1446 rpm the 3.55 will downshift to 8th. The 3.31 may or may not need to shift. If they both drop another gear the 3.55 will be in 8th running 1789 rpm ... the 3.31 equipped truck will be in 7th at 1963 rpm. Again the 3.55 is more likely to require an additional shift than is the 3.31 equipped truck but say the both drop another gear. The 3.55 will be in 7th at 2105 rpm and the 3.31 equipped truck will be in 6th at 2506 rpm. At this point you are on a fairly significant hill if all you're pulling is 16k lbs. More than likely the 3.31 is going to pull the hill the 3.55 equipped truck might need to downshift again.

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