No harm...

Yes, I am old north of 65... been wrenching on cars since I was 13...

 

I was wondering Chuck, what kind of milage did you see with your rig setup in general? I ask because I have a buddy that tows his 5th around the us quite a bit and he has purchased a 2016 6.7 cclb srw. He recently upgraded his 5th to a triple axel and when he did about 4k round trip from Oregon to somewhere back east he averaged 11.5 with a truck and trailer combined weight of 27,200 when he scaled it.

Not a gas vs diesel question here. Just pondering what milage you get vs what my buddy got recently, plus the fact that the op didn't give more specifications on trailer size and such. Might also give him a better idea of he wants to look at a 6.7 or if regearing his 6.2 would be a better option for him.

 

You are correct in your assumptions and calculations.

I ignore power ratings generally; that concept (while we all recognize the core intent) is really only torque rated at a particular rpm. Rather than saying "My truck has xxx Ft-Lb at yyyy rpm", it's just a mathematical formula of .... (T x rpm) / 5252. We could just as easily make up a new standard called "toothpaste power" or "elephant power" or "camera power"; as long as we define at what rpm the criteria would measured it, it's all relative.

What moves a vehicle (or makes it resistive to movement) is force. Force is mass x acceleration.

To move the truck forward the "thrust" (measured in pounds of force) needs to be greater than the resistant force of it sitting still. There is static force (a steady state) or dynamic force (acceleration).


Bottom line is this: the quote above (reasonably ignoring the parasitic loss topics) does exactly show how the torque is multiplied.

All you have to do to figure the "force" is divide that rear wheel torque by the diameter of the tire.


Simple HS physics math.

 

Sorry guys I didn't think this would spark such a lively debate! The new to us Fifth wheel is a 2011 Open Range 337 rls. While on paper it doesn't weigh that much empty , around 9,000lbs, when loaded up it probably approaches 10,500 plus lbs for cross country touring. We go from Ontario Canada directly south to the Southern U.S across to Arizona & California and then up the west coast and into B.C and return in under a month. This is a journey we do once a year, round trip of 7,000 miles plus many more journeys in Ontario during the rest of the year, the truck is rarely unhitched from the rv. A weekend getaway for us is 600 miles (Ontario is huge). Our previous fifth wheel was a light model with a low profile front. I didn't calculate that wind resistance would be such a factor in the towing but it definitely is. So my concern is the long journey and western mountains with the heavier, loaded up rv and added wind resistance plus larger waste and water tanks, & a full fuel load, could make what was a pleasant experience into a chore. The 15% increase in torque is it correct to say that max 400 ft lbs of torque the 6.2 has now it would increase it by an equivalent of adding 60ft lbs?

 

maybe 50 ft lbs... 400 + 50 = 450

diesel is like 800 ??????

as for Lively... that has been going on since the 1940's. maybe the 30's.
I remember the debates in high school Shop class in like 1965...

Gas/diesel/ high gears/low gears/ tall wheels/low wheels.

 

Brickman,
Remember, you asked for how much torque and power would increase. So if you put your truck on a chassis dyno with the 3.73 gears and then again with the 4.30 gears you should measure about a 15% increase in torque and power as measured by the chassis dyno. This is done with the engine at wide open throttle. When pulling a camper, a perhaps better way to look at it is the stress on your engine and tranny will be about 15% less. Though I guess it's okay to think of it as having 15% more engine torque...6 of one...half a dozen of the other....

 

Essentially, it would be the equivlant; yes.

We presume you understand that modifying the gears does not alter the engine's ability to produce torque. It's actually modifying the drain-train ability to multiply torque.

Again, what moves the object is force. The formula to determine this "thrust" (force) is taking the available torque at the rear wheel tire surface, and then dividing by the tire radius (the moment arm). Presuming all other things are not changed (engine stays the same, tranny stays the same, tires stay the same), then the change in rear-diff gearing will produce a relative ratio of change. Going from 3.73 to 4.30 is (roughly) equivilant to a 15% torque multiplier.

If you want to think of it as "engine" multiplication, then it would be essentially the same as adding 60 Ft-LB at the engine, but still having the 3.73 gears. If this helps you understand the relative effect, then so be it.

 

Thanks everyone for their helpful input. After looking into getting the 4:30 gear set proved difficult to find a shop in my area that could do the work, and looking at how I use the truck, I have decided to order a 2017 F350 SC Lariat dually with 6.7 I can't say enough good things about the 6.2, a superb drivetrain and I hope this 6.7 will be as reliable.

 

Congrats Brickman I'm so glad you are getting a dually they feel like you are on a rail when you drive them.