Towing with 6.4 hemi

[HEMIMANN]

Well I suppose truck configuration plays a part. But this is why I love my 3.21 for towing. Because it wants to tow in 6th at 2200 RPMs and loves that spot. It's that perfect balance of having power in reserve, but not revving too high. It would often upshift into 7th if I let it, but it's not all that happy there with frequent downshifts, and in 7th it's in OD and I'm certain that is hard on the transmission.

If I had the 3.92 and locked it down to 6th, I'd be needlessly over revving at like 2800 or whatever it would be, so then I'd lock it down to 7th to get that same balance of power and low rpms, but then I'd be towing in OD for hours and I just don't think that's good for it. Whenever I tried letting my truck upshift into 7th I'd see transmission temps go up a little.

Would that matter? Your net rpm would be near the same engine through transmission and torque would be equal.

What you'd have is another drop down gear for higher grades.
But maybe 8 gears is enough so as to be able to drop to 3.21 axle so max mileage when dead heading?

 

[ramffml]

Would that matter? Your net rpm would be near the same engine through transmission and torque would be equal.

That's a good question, I don't know to be honest. I just note the little increase in temps when I upshift to 7th and let it chew on that for a few mins.

What you'd have is another drop down gear for higher grades.
But maybe 8 gears is enough so as to be able to drop to 3.21 axle so max mileage when dead heading?

So for my trailer/load I only use 6 gears for towing, and it's plenty for me. Probably heavier loads in a 2500 might be a different story, but the gear ratios are quite close already.

Really what the 3.92 gives you is a deeper first gear, like a granny gear, but the 3.21 with a 5:1 first gear is already very deep, even deeper than (say) the old tundra with a 6 speed and 4:30 rear end (I just remember that because I got into an argument with a guy on reddit once and did the math for him). 3.92 and 5:1 first gear is even more deep but I don't need more power off the line from a stop. I can use a bit more in 3rd or 4th when I'm on the onramps trying to get up to speed but the 3.92 doesn't offer more ratios at those speeds, the advantage of its first gear is long gone.

 

[HEMIMANN]

It's a great issue to ponder compared to those of us milking our RFE's lol.

I am thankful for being invited to this group to learn how to maximize longevity from the marginally designed components on these trucks. And still the most comfortable truck I've ever owned.

 

[Ribtipram]

I pull a 13000# fifthwheel . 6.4 373 gears. It's no diesel but I feel it hauls fine.

 

[Ribtipram]

6 speed also