2018 Dodge 3500 dually gas motor row ratings

RoyJ wrote:
Here's an EXTREME example of startability - getting 141,000 lbs rolling:

https://www.youtube.com/watch?v=13hBEX0ANVk

As soon as he's rolling in a stead gear, a gasser of equal hp could do euqally as well. Let's say a 640 big block pumping out 600+ hp.

But now we're talking gradability, not startability.

So you kinda disproved your own point. Torque gets you up hills. HP decides how fast.
If the 600hp big block is pulling a load that requires less than full torque input to maintain speed (i.e. Able to accelerate), it will be able to accelerate faster, in general than the 400 hp diesel. Once the grade or load requires more than the 500-600 ft lbs that the gasser is able to produce (assuming right rpms for top of torque curve), the 400 hp diesel will walk it because it's still able to maintain speed.
Remember without torque, there is no horsepower.

That's an impressive pull for that pickup though.

ib516 wrote:
That's the first I've heard of TM on a 6.4L Hemi, got a link to a source? I'm not challenging you, just curious as I plan to buy another.

In any case, I think we can agree a diesel is a better choice when "how it performs when towing a heavy load" is the only parameter you measure the trucks' worthiness by. When you add in initial cost, short commuting driving, winter cabin heat in extreme cold, maintenance cost, payload, and a few other parameters, it's not so black and white.

I don't have OEM proof at this point, but safe to say every modern car has torque management. Maybe not necessarily de-rating the peak torque output like the diesels, but they'll delay torque ramp-up off the line.

Even assuming the 6.4 can put 100% of its torque off the line, the Cummins would have to be de-rated to 400 lb-ft to be as weak. And I highly doubt that! So that aside, can you think of any other reason Ram would lower the 6.4 towing capacity that much?

And just so you know, I'm a huge proponent of modern gas powertrains, ever since the 2007 diesel emissions nightmares. I've read nearly every one of your past towing experiences with the 6.4, and even stole your photos to prove to other the coil springs can handle pin weight just as well as leafs.

But I'm making one exception this time because I truly believe gas engines can match a diesel's off the line startability.

RoyJ wrote:

ib516 wrote:
Unfortunately, your calculation completely leaves out the fact that all modern high torque diesels in pickups with auto transmissions are equipped with the transmission saving TORQUE MANAGEMENT (torque reduction) feature in the lower gears. There's no way you're getting anywhere near 930 lb-ft in gear 1 and 2.

I have actually tested it. In the real world. I used my previous 6.4L Hemi/4.10 vs a friends 3500 SRW Cummins/3.42. The trucks were identical with the exception of the transmission (66RFE vs 68RFE), rear axle ratio, rear suspension, and engine. We did 0-60 mph towing his 14k 5er. Guess who was faster to 60 mph? My Hemi was.

Unsurprisingly, I was faster 0-60 empty as well. That only makes sense. Lighter truck, 4.10 gears, and more hp.

It's a good point you brought up, but BOTH the Hemi and Cummins has torque management.

But a 0-60 run is not a good measurement of startability. You're well into the meat of the power band where raw HP, rather than torque, does the work (see my post above). Your HEMI was faster because it has more HP, my little 5.7 can easily out pull a stock 24V Cummins on highway grades.

A better test would be finding a steep hill and test it at full GVW.

Even if my numbers aren't 100% true to life, it still brings up an area where diesels are superior to gas. As we step into 8 or 10 speed transmission, this gap will shrink.

That's the first I've heard of TM on a 6.4L Hemi, got a link to a source? I'm not challenging you, just curious as I plan to buy another.

In any case, I think we can agree a diesel is a better choice when "how it performs when towing a heavy load" is the only parameter you measure the trucks' worthiness by. When you add in initial cost, short commuting driving, winter cabin heat in extreme cold, maintenance cost, payload, and a few other parameters, it's not so black and white.

Here's an EXTREME example of startability - getting 141,000 lbs rolling:

https://www.youtube.com/watch?v=13hBEX0ANVk

As soon as he's rolling in a stead gear, a gasser of equal hp could do euqally as well. Let's say a 640 big block pumping out 600+ hp.

But now we're talking gradability, not startability.

ib516 wrote:
Unfortunately, your calculation completely leaves out the fact that all modern high torque diesels in pickups with auto transmissions are equipped with the transmission saving TORQUE MANAGEMENT (torque reduction) feature in the lower gears. There's no way you're getting anywhere near 930 lb-ft in gear 1 and 2.

I have actually tested it. In the real world. I used my previous 6.4L Hemi/4.10 vs a friends 3500 SRW Cummins/3.42. The trucks were identical with the exception of the transmission (66RFE vs 68RFE), rear axle ratio, rear suspension, and engine. We did 0-60 mph towing his 14k 5er. Guess who was faster to 60 mph? My Hemi was.

Unsurprisingly, I was faster 0-60 empty as well. That only makes sense. Lighter truck, 4.10 gears, and more hp.

It's a good point you brought up, but BOTH the Hemi and Cummins has torque management.

But a 0-60 run is not a good measurement of startability. You're well into the meat of the power band where raw HP, rather than torque, does the work (see my post above). Your HEMI was faster because it has more HP, my little 5.7 can easily out pull a stock 24V Cummins on highway grades.

A better test would be finding a steep hill and test it at full GVW.

Even if my numbers aren't 100% true to life, it still brings up an area where diesels are superior to gas. As we step into 8 or 10 speed transmission, this gap will shrink.

dodge guy wrote:

Roy J wrote:
Normally, I always correct people on the "torque vs HP" argument - as it's hp that pulls you up grades, not torque.

So you mean to say an engine with 200HP and 250lbft of TQ will get up a hill better than one with 200HP and 400lbft of TQ?

With a perfect CVT - absolutely identical. No better, no worse.

In a real life example: 5.7 HEMI with 395hp / 409 lb-ft, 8 spd ZF, will beat a Gen 2 Cummins with 250 hp / 505 lb-ft, any day, any time, any where.

When was the last time we saw a GE locomotive rated in torque of their prime movers? a 6000 hp locomotive out pulls a 4400 hp, regardless of torque.

I'm in a weird spot. For the weights that I'm pulling now and in the near future, I don't need a diesel. My packed weights on the TT are a usually 9k and I'm not pulling more than 13k with other trailers. However, for the weights I'm often carrying I need a dually.

I ended up with a 18' 6.4 Mega Cab Dually Laramie. It's a pretty rare truck and had to put in an order for it. I wanted a 4.10's, but it came with 3.73's. I'm doing fine with the 3.73 and not thinking of swapping gears. I'm coming up on the year mark and it's got a little over 24,000 miles on it. So far I haven't been disappointed with anything about the truck.

RoyJ wrote:
Normally, I always correct people on the "torque vs HP" argument - as it's hp that pulls you up grades, not torque.

However, this is one exception where the TORQUE of the Cummins allows it for the much higher tow rating. An important spec in tow rating is startability - ability to pull away from a steep grade.

Cummins / Aisin: 930 lb-ft x 3.75 (1st gear ratio) x 4.10 = 14,299 lb-ft rear axle torque. With 33" tire gives 10,400 lbs of tractive effort.

6.4 HEMI / 66RE: 429 lb-ft x 3.23 x 4.10 = 5,681 lb-ft axle torque. With 33" tire gives 4,132 lbs of tractive effort.

The gas engine has only 40% of the starting tractive effort of the Cummins!

This means even with a 15,600 lbs trailer (23,400 GVW), the 6.4 gets beat off the line by a Cummins / Aisin towing 30,320 lbs trailer (39,100 GVW).

Simple math tells us the HEMI can only start out on a 17.7% grade, while the Cummins can pull away from a 26.6% grade!

In real life, the Cummins would perform even better as its torque peak (1700rpm) is much closer to the converter stall than the HEMI (4000rpm).

Unfortunately, your calculation completely leaves out the fact that all modern high torque diesels in pickups with auto transmissions are equipped with the transmission saving TORQUE MANAGEMENT (torque reduction) feature in the lower gears. There's no way you're getting anywhere near 930 lb-ft in gear 1 and 2.

I have actually tested it. In the real world. I used my previous 6.4L Hemi/4.10 vs a friends 3500 SRW Cummins/3.42. The trucks were identical with the exception of the transmission (66RFE vs 68RFE), rear axle ratio, rear suspension, and engine. We did 0-60 mph towing his 14k 5er. Guess who was faster to 60 mph? My Hemi was.

Unsurprisingly, I was faster 0-60 empty as well. That only makes sense. Lighter truck, 4.10 gears, and more hp.

RoyJ wrote:
Normally, I always correct people on the "torque vs HP" argument - as it's hp that pulls you up grades, not torque.

However, this is one exception where the TORQUE of the Cummins allows it for the much higher tow rating. An important spec in tow rating is startability - ability to pull away from a steep grade.

Cummins / Aisin: 930 lb-ft x 3.75 (1st gear ratio) x 4.10 = 14,299 lb-ft rear axle torque. With 33" tire gives 10,400 lbs of tractive effort.

6.4 HEMI / 66RE: 429 lb-ft x 3.23 x 4.10 = 5,681 lb-ft axle torque. With 33" tire gives 4,132 lbs of tractive effort.

The gas engine has only 40% of the starting tractive effort of the Cummins!

This means even with a 15,600 lbs trailer (23,400 GVW), the 6.4 gets beat off the line by a Cummins / Aisin towing 30,320 lbs trailer (39,100 GVW).

Simple math tells us the HEMI can only start out on a 17.7% grade, while the Cummins can pull away from a 26.6% grade!

In real life, the Cummins would perform even better as its torque peak (1700rpm) is much closer to the converter stall than the HEMI (4000rpm).

Nice explanation.

I have ended up starting out on some fairly steep grades towing 33-35k combined with the AISIN/4.10/Cummins combo. Not a single bit if shudder or axle bounce, it simply took off!

Roy J wrote:
Normally, I always correct people on the "torque vs HP" argument - as it's hp that pulls you up grades, not torque.

So you mean to say an engine with 200HP and 250lbft of TQ will get up a hill better than one with 200HP and 400lbft of TQ?