I am not sure I agree with the above statement. I believe all diesel motors make peak torque and peak hp at about the same spots in the rpm range. I also believe that the rev limiter for a stock diesel is about 3250 for all 3 brands of diesel trucks. So if the trucks have about the same hp and torque and none of the trucks rev higher than the other one, the one with the most gears and the least amount of weight ought to pull to the top of the hill the fastest.

 

The stock 6L PSD rev limits around 3850. Peak HP/TQ is higher in the PSD. That's good for highway pulling, but weaker for starting out. 'Course you only start once, but haul down the highway all day long.

The point I'm trying to make is since the V8s can rev higher and still produce power, they have a gearing advantage. For example, pulling a big load up the steepest hill, ALL the big 3 trucks would need to downshift. When the V8's downshift, they are still in the powerband and can maintain speed. When the I6 downshifts, it drops out of it's powerband, loses speed, etc.

All I'm saying is for highway hauling in a light duty pickup frame, a V8 is superior. But for low rpm tractor work (or if you have a gazillon gears available), an I6 beats a V8.

 

I am not sure that I follow your logic here.

Torque is a measure of work. Power is the time rate of delivering torque.

In simple terms, torque is a measure of how much of a load a truck can pull. HP is a measure of how fast the truck can deliver that torque, or get it up to speed.

High torque/low HP = can pull stumps, but not very fast

Low torque/high HP = can't pull very big stumps, but can do it in a hurry.

OK. This is an over-simplification, I know. But it does illustrate the point.

So, at 65 mph, my 7.3 turns about 1750 rpm. Smack at the peak of the torque curve. HP, however, doesn't peak until 2700-2800 rpm, so the engine is not putting out much HP.

So what does this mean to me? Going down the road, my X can hold 65 mph up some decent hills, even when pulling a 9000 lbs. trailer. But if I slow down to 60 mph on a hill, I probably cannot accelerate back up to 65 mph, and definitely not without downshifting and getting the revs up.

So, is this consistent with what you are saying? Are we agreeing? Because I am not sure that we are.

BTW - my '05 CDI can walk away from my 7.3, so I don't know that being an I6 has handicapped it that much, and the 7.3 being a V-8 doesn't help it much

 

i never realized that the stroker had such a high rev. holy cow the dmax is hitting a rev limiter at the same spot as the cummins. about 3200-3300.

 

I dunno.

All the trannies of the big3 have very similar gear ratios. We all are about the same rpms/speed. So on the steepest of hills, everyone is going to have to downshift pulling a large load (similar engine ratings). I'm saying the V8s can still maintain speed because their powerband is higher in the rpms. The I6s will rev up beyond the optimal powerband and have to slow down to get rpms in the powerband.

To keep up with the V8s, an I6 needs more gears so that downshift will keep the rpms in the powerband. The problem is there isn't enough room under our light-duty pickups. Mopar's is currently only a 4 speed. A 6-speed should help of course. But I don't know if it'll be enough to overtake the V8s.

 

OK. The V-8s tend to produce max HP at higher RPMs than I6's.

But I am not sure that HP has as much to do with maintaining speed as torque.

 

It doesn't.


Since the Powerstroke has its "power" in higher in the powerband, it would need to downshift when going up a hill whereas the Cummins can stay in gear and chug right along afforded by its lower powerband.
Sounds like by his logic since a V8 has a Higher power band that it needs more gears to downshift into so the engine can rev higher and maintain peak "Power".

 

That's the flexibility of the PSD. They can downshift and maintain speed as TQ stays on at higher rpms. When CTD downshifts, it'll fall sorely behind. There are better applications for I6's, but in the light duty truck market they fall behind. That's why 2 of the big 3 use V8's. There's only so many gears you can fit under the truck. Flexibility and cost savings.

 

I don't know... Driving around Oregon, especially through the Mt. passes, I'm hard pressed to see ANY new diesel pick up "fall sorely behind" even while hauling fully loaded 5th wheels. Now I do see plenty of new F-150s struggle keep at 45 towing their TT or boats up the same hills, but thats another topic.

 

OK. Now you lost me.

You see, my CDI has never had to downshift, even when pulling almost 11,000 lbs.

 

Flatlander.

 

Good thing I have my salt shaker handy. Need a grain or two.

 

Dodge is waking up very soon. The 5.9L Will run until December. They will be switching to a 6.7L Cummins in Jan 07. 350 HP, 650 Tq, available with a 6 Speed AUTO. Finally.

 

This should help you:

Diesel Towing Competitions.

2003 MY:

http://www.fourwheeler.com/roadtests...el/index3.html


2004 MY (yes with the HO cummings...and Ford STILL wins):

1) http://dieselpowermag.com/features/0411dpm_shootout/
"The competition is fierce, but Dodge and GMC have a little more homework to do if they want to top our diesel hauler winner, the '04 Ford Super Duty."

2005 MY

1) https://www.ford-trucks.com/news/idx...rst_Drive.html

"With the diesels, the Dodge/Cummins pulled off the line the quickest, the GMC Duramax next and the Ford Power Stroke last. The Dodge's narrow power band quickly revealed itself and both the Ford and GMC pulled ahead before 30 mph was reached. The Ford and GMC stayed nearly even until about 30 mph and then the Ford started pulling ahead, winning by a full truck/trailer length by the time it hit 60 mph."

 

Hopefully by that time, the dmax will have 400 and 700. LOL

I see both sides of the arguement on teh I6 vs the V8. if it gets to the point were the cummins has to go down a gear and can't lug the hill, the powerstroke in theory should pull the hill at a high speed.