gas vs. diesel hauling

[DirtFarmer]

Let's take a look at GM's 8.1. It is making 400lbs-ft @ about 1100 to a Peak of 450@3200 back down to 400lbs-ft @ 4500 RPMS. 3400 RPMS of above 400lbs-ft. Not many Stock diesel pickups are over 400lbs-ft for 3400 RPMs.

This is good info, but to me, I really don't care what an engine will do at 4500 rpm or even 3200 rpm because I don't want to run at those rpms! Big numbers at high rpm will give you good acceleration, but once I'm up to speed, I want to run somewhere around 2000 rpm.

To me, the diesel's ability to pull a big trailer down the road in OD is it's #1 advantage over a gasser.

To answer the original question:

A small block gasser will tow a few thousand pounds very easily. It'll do OK with 5 or 6 thousand (in straight gear, not OD). Beyond that, it'll start to suck wind. Any small incline or strong headwind and you'll be downshifting again and the rpm will be high and the road speed aggravatingly low.

As was said above, if you don't tow very often, you can live with some pain from being under-motored.

Do it everyday and it'll make you

 

[tgatch]

You missed the point. Pull a 6% grade where you need the dig. I promise you, you will NOT be at 2,000 RPMs. I pull a long 6% grade and my truck is humming along at 2500 RPMS at about 55MPH with my 13,000lbs 5th wheel in tow. I promise you that the big block from GM will be right there with me while my truck is in a stock tune.

At 2,000 RPMs you are making somewhere in the ballpark of 200HP IF your are running wide open throttle with your 7.3. The 8.1 would be making about 160HP at the same rpm IF it is being run wide open. Problem is you have 235 HP while the 8.1 has 330 HP, so it can and will pass you on a long grade assuming you are stock.

Let's look at it another way. Say we are pulling a 6% grade with a 12' tall x 8' wide trailer with a running clearance of 12" and a GCW of 20,000lbs. Say we want to pull that hill at 60 mph. Using a spreadsheet that was built from calcualations for equiping a MDT truck it requires ~369HP. Guess what, your 235 HP diesel is NOT enough to maintain 60 MPH up a 6% grade. But the 330HP 8.1 will walk away from you and be much closer to that 60MPH. 45 mph will be about it for a 235HP 7.3 while the 8.1 will be about 56MPH. BTW, the spreadsheet has been pretty accurate in predicting the behaviors I have seen when towing with my 5.4 F150 and my Powerstroke F350.

I have towed with an 8.1 it will pull along at 2,000 RPMS just fine for most of the flat towing. Get in the hills and stock for stock an 8.1 will hang with and walk away from most of the diesels that are out there in the pickup truck ranks. The difference? The 8.1 will be in single digit mileage while us diesel owners will be in double digit mileage. Considering that 87 Octane is 2.90 a gallon here and diesel is 3.50 a gallon, I'd say that the $$ spent per mile is pretty dang close.

I will leave it at this as nothing I am going to say is going to convince you that the facts are what they are. No one tows a 6 or 7% grade at 2000 RPMS. Either engine will pull in OD at 70 MPH on the flats. The 8.1 has more HP so it WILL be able to pull a grade faster than most stock diesel pickups. The 8.1 will get less mileage, but at $0.60 more a gallon for diesel here in Idaho that is almost a wash. No I am not trying to convince you to trade in your 7.3 on an 8.1 Big block gas engine. Just pointing out the facts.

 

[RKOCH]

But my 7.3 will get better millage than that 8.1 any day of the week. This I know and have seen with my own eyes.

 

[tgatch]

But my 7.3 will get better millage than that 8.1 any day of the week. This I know and have seen with my own eyes.

And that I will not argue. The question posed was when does it make sense to go to diesel over gas when it comes to weight. I stated that it is more a mileage thing than it is a weight thing.

Someone pointed out that all OTR trucks are diesel. I merely pointed out that those trucks are diesel because they are more fuel efficient and they generally last longer. I would say that a 14 liter gas engine could hold its own against a 14 liter diesel engine. It just won't last as long and it would not get the same mileage.

Like I said, the facts are what they are.

Please notice, I DO own a diesel not a gas pickup.

 

[DirtFarmer]

I will leave it at this as nothing I am going to say is going to convince you that the facts are what they are..... Just pointing out the facts.

There's nothing for you to convince me of because we're in 100% agreement.

By your numbers, the PSD has 25% more torque at 2000rpm than the 8.1. That supports my butt-O-meter from pulling similar trailers with 460 (two of mine) 454 (one of mine) and 8.1 (buddy).

To overcome the lower torque, I've often had to downshift once (relative to PSD) in the gas burners. You point out that if the gas burner downshifted twice instead of once and charged up the hill (at a bazillion rpm), he'd actually be the first one to the top. I don't doubt that.

I simply stated that given a choice, I'd pick the truck that can run in a higher gear - and that is inevitably a diesel.

Mark

ps: Do you pull a 13,000lb trailer with a SRW pickup?!?

 

[Batman]

Back a few years ago, I towed an EMPTY 16 cargo trailer from Rhode Island to Arizona. The truck was a99 Dodge Ram with a 318 auto. It had around 36k miles on it. I had bought it new, and treated it well, properly maintained, etc.
I didn't to at excesive speeds. However, the engine had a rod knock in it when I reached Arizona.

From that point, it was diesel all the way with no turning back.

I know there could have been more than just that one long tow to cause the enigne problem, However, as stated on previous responses, there is a reason the big rigs run diesel.

Additionally, the new truck I got in AZ has training wheels, which to me, is more safe when towing.
HTH
George

 

[tgatch]

There's nothing for you to convince me of because we're in 100% agreement.

By your numbers, the PSD has 25% more torque at 2000rpm than the 8.1. That supports my butt-O-meter from pulling similar trailers with 460 (two of mine) 454 (one of mine) and 8.1 (buddy).

To overcome the lower torque, I've often had to downshift once (relative to PSD) in the gas burners. You point out that if the gas burner downshifted twice instead of once and charged up the hill (at a bazillion rpm), he'd actually be the first one to the top. I don't doubt that.

I simply stated that given a choice, I'd pick the truck that can run in a higher gear - and that is inevitably a diesel.

Mark

ps: Do you pull a 13,000lb trailer with a SRW pickup?!?

Just remember turning 2500RPMs in a a PSD is like turning 3200 to 3500 in a Big Block Gas engine. So the RPM idea has to be kept in context. Sure it will spin a few K higher, but that is what it is designed to do.

And yes I tow 13,000lbs with a SRW truck. I rolled over the scales recently loaded up for a trip with a full tank. Steer had 4100 on it, Drive had 5700 on it, and the trailer axles were at 10,400. The truck with my 180lbs but in has weights as follows, 4220 Steer and 2880 drive. I'm under my GVWR and GAWR. I am about 300 over my GCWR which I would be even more with a dually as a Dually would weigh in at about 400lbs more than my truck.

And Batman, a 318 is no fair comparisson to a diesel truck. If you are going to pull Dodge engines out like that, lets look at the old 440. My dad had one in a 10,000lbs Class C that could light the tires on demand from a stop.

 

[DirtFarmer]

And yes I tow 13,000lbs with a SRW truck. I rolled over the scales recently loaded up for a trip with a full tank. Steer had 4100 on it, Drive had 5700 on it, and the trailer axles were at 10,400. The truck with my 180lbs but in has weights as follows, 4220 Steer and 2880 drive.

13,000 sounds very borderline for a SRW pickup. I would have expected that you'd be over GVWR (and very close to, if not over GAWR) when fully loaded but I guess different trailers are balanced more towards the rear. What is the GAWR on your SRW SD? I was thinking that it was less than 6000lbs?

I'm under my GVWR and GAWR. I am about 300 over my GCWR which I would be even more with a dually as a Dually would weigh in at about 400lbs more than my truck.

Are you implying that SRW is the best/safest choice to tow 13,000lbs?

Generally, the GCWR is considered the "least important" of the ratings. Axle, tire and GVWR ratings can be found on the vehicle. GCWR is only found in Ford literature.

I'd rather cheat a little on the GCWR if that is the price to pay to give me capacity to spare in GVWR, GAWR and tire ratings.

 

[tgatch]

RAWR on my truck is 6830. The weight I listed above was fully loaded.

I am just a hair under the GVWR. And I agree that being over on the GCWR is better than being over on any of the other ratings. The fact is, I am under on everything BUT my GCWR.

I was not implying that a SRW was a safer choice. I have the truck that I need and what will fit with what I use it for most of the time. I am sure that a DRW would feel a little more secure with the load. If I was towing more than I do I would probably go to a DRW or maybe even a Medium Duty Truck. Heck for about $10,000 I could buy a Single axle big rig with about 500K in the odometer and have way more than enough truck.

 

[DirtFarmer]

RAWR on my truck is 6830. The weight I listed above was fully loaded.

That's cool. I guess those numbers have crept up over the years.

I am just a hair under the GVWR. And I agree that being over on the GCWR is better than being over on any of the other ratings. The fact is, I am under on everything BUT my GCWR.

Sounds good. I guess my figures were out of date.

Happy towing!

 

[TheBAT]

I bought my diesel for the mileage, the sound, and the cool factor...

 

[BigSix]

We tow 10,040 lbs of high profile 5th wheel with our small block gasser. Not a problem around th southeast. With our previous Cummins powered Rams, we towed in O/D at 2100rpm and direct at 2900rpm on the steeper uphills. With the Hemi, we tow in direct at 2800rpm and 2nd gear at 4200rpm on the steeper uphills. On flat ground with no wind, it'll drop into 4th (.75 O/D). The Cummins got 10.5~mpg towing 68mpg and the Hemi gets 8.5mpg towing 68mph. The Cummins could last a million miles but I don't plan on keeping a truck 40yrs. The Hemi could last 300k miles but I won't keep it 12yrs either. Both are great engines and are both listed in the top ten engines.
If I'm ever in the market for an OTR commercial tow vehicle to put 2500 miles a week on and tow 70,000+ GCW, I'll definately consider diesel. But mine is a pickup truck. Either engine does a fantastic job.

 

[Brickman]

Back to the topic. An 8.1 from GM or the V-10 from Ford will pull just as well as a diesel. Anyone that says different hasn't driven them, or they are at much higher altitudes.

At least that is how I would look at it.

If you are talking stock you maybe close to right. But all the diesels are much easier to gain HP and torque out of them with a few mods than what a gasser will. And then there is NO comparison.

 

[tgatch]

If you are talking stock you maybe close to right. But all the diesels are much easier to gain HP and torque out of them with a few mods than what a gasser will. And then there is NO comparison.

I never argued that. As a matter of act I did mention "stock for stock" a couple times. There is no close about it... I know I am right. I have seen two GMC trucks that were about as identical as it gets pulling identical toyhaulers up Baker Grade on I-15. They were both stock one diesel the other an 8.1. Both were very close in weight. The Duramax got the initial jump when they started, but the 8.1 stretched its legs on the top end and pulled right on past the Duramax. Why? 300HP vs 340HP. The Duramax got the intial jump because of the torque on the bottom end. Now if we were comparing who holds OD longer on a climb, the Duramax wins over the 8.1.

The question at the beginning of this thread was:

At what weight does it simply make more sense to pull with a diesel rather than a gasser, either economically or the truck itself?

I stated that weight isn't so much the issue. (Save for the new tow boss F350). The 8.1 has the same GCWR as the Duramax. Up until 2005 the V-10 had the same GCWR as the Powerstroke (7.3 or 6.0). What I said was that it is more an economy of miles. Tow 10,000lbs for 5,000 miles per year and either will do the job and do it well. Tow 10,000lbs for 50,000miles per year, diesel wins hands down. Why? The stops at the fill up station will answer that.

I guess that is about as clear as I can state it.

 

[RLDSL]

A couple of years ago My car broke down in upstate NY and I had to rent a Uhaul truck and car trailer to get it home. All they had was a big truck with a V10 gasser. While I was downright impressed at the power( I honestly had a hard time telling that there was a car behind the thing ) the fuel milage was deplorable. That beast had a huge tank, but I had to stop and fill the thing more often than I needed to stop to ***. I just about had wallet failure feeding that thing. Maybe 5 mpg on flat stretches with a tailwind.The truck only had about 20k miles on it and it ate oil.

My old '92 7.3 diesel f350 gets 2-3 times or better the fuel mileage.

For me it's no contest, but then, I drive a diesel car too

-------Robert