Towing with a 6.2?

[noahrob]

Good stuff, the simple version is that torque is how hard it spins and horsepower is how fast it spins (RPM). This is especially important on a motorcycle. I will always take a twin over an inline four becasue of the torque...how fast can it get going v. how fast can it go.

Of course a GSXR is faster than an RC51, but that RC51 can fly off the line.

And then to the point of gearing, you can change the powerband all over teh place.

So, for towing, I want torque to get my trailer etc..moving, but I need that engine to keep spinning as I climb the hill...through gearing I can keep my truck in the sweet spot at a given speed.

This is a great thread.

For a given torque, the equivalent power may be calculated. The standard equation relating torque in foot-pounds, rotational speed in RPM and horsepower is:

 

[6.2Blazer]

While MaxPF's technical information is not necessarily wrong per se, he's leaving out several details that are pretty important in the real world situation. He keeps mentioning the amount of work engines with the same horsepower can perform, okay, okay, get a calculator out and you can prove this (basically the amount of mass you can move some "x" distance vertically). However he leaves out the whole idea of how fast the work is performed. Sure, a 4-banger Honda engine could pull an 80,000 lb. semi up a 6% grade, and yes you could gear it to provide the same torque at the wheels as a typical big rig engine...he's just leaving out the fact that you would be spinning the little 4-banger at 7,000 rpm while you traveled at 10 mph (I'm just throwing those numbers out to get the point across, so please refrain from the "well, my Honda redlines at 6,750 rpm" or "I did a bunch of calcuations and you would be going 17 mph" comments ).

There is a direct relationship between the engine rpm and the gearing. You can add more gearing to get the same torque, but you will correspondingly lower the speed of the vehicle. If engine "A" has half the torque as engine "B", you will need twice the gearing for the same torque at the wheels. So the choices are either:
1. vehicle with engine "A" runs half the speed as "B"
2. run engine "A" at twice the rpm as engine "B"
(assuming the torque curves per rpm were the same)

And come on now, don't go try to justify your point with "I'm only talking about the later 6.2's with 165 hp, and not the old ones with only 155 hp (6% BTW ), or "you said similiar, not exactly the same weight"...I'm talking about a 6,500 lb. K5 on a 2,500 lb. trailer behind a 7,000 lb. truck = 16,000 lb. Even if the other truck was 1,000 lbs. lighter (which I doubt) you are talking 5-6% difference and that is NOT enough of difference to fly by the other truck on the grade.

Not sure what you consider "decent towing gears" behind a 6.2, but get any lower than what was commonly found under factory 3/4 and 1-ton trucks and you can't even run the speed limit with one.

 

[MaxPF]

While MaxPF's technical information is not necessarily wrong per se, he's leaving out several details that are pretty important in the real world situation. He keeps mentioning the amount of work engines with the same horsepower can perform, okay, okay, get a calculator out and you can prove this (basically the amount of mass you can move some "x" distance vertically). However he leaves out the whole idea of how fast the work is performed.

How fast work is performed is called HORSEPOWER! Please read those links again.

Sure, a 4-banger Honda engine could pull an 80,000 lb. semi up a 6% grade, and yes you could gear it to provide the same torque at the wheels as a typical big rig engine...he's just leaving out the fact that you would be spinning the little 4-banger at 7,000 rpm while you traveled at 10 mph (I'm just throwing those numbers out to get the point across, so please refrain from the "well, my Honda redlines at 6,750 rpm" or "I did a bunch of calcuations and you would be going 17 mph" comments ).

I never compared a Honda to a big rig engine. The big rig engine has more HP than the Honda, hence it can perform more work in a given amount of time.

There is a direct relationship between the engine rpm and the gearing. You can add more gearing to get the same torque, but you will correspondingly lower the speed of the vehicle. If engine "A" has half the torque as engine "B", you will need twice the gearing for the same torque at the wheels. So the choices are either:
1. vehicle with engine "A" runs half the speed as "B"
2. run engine "A" at twice the rpm as engine "B"
(assuming the torque curves per rpm were the same)

IF engine A has half the torque as B at twice the RPM, then both will move the vehicle at the same speed with appropriate gearing. See my above example of exactly that case.

And come on now, don't go try to justify your point with "I'm only talking about the later 6.2's with 165 hp, and not the old ones with only 155 hp (6% BTW ), or "you said similiar, not exactly the same weight"...I'm talking about a 6,500 lb. K5 on a 2,500 lb. trailer behind a 7,000 lb. truck = 16,000 lb. Even if the other truck was 1,000 lbs. lighter (which I doubt) you are talking 5-6% difference and that is NOT enough of difference to fly by the other truck on the grade.

I have to specify the engines - obviusly an engine with less HP won't tow as fast as one with more. IT's also apparent that the gearing in the DMax truck was closer to optimal than your 6.0 gasser. I also asked what RPM you were running with your 6.0. You gotta spin the snot out of that motor to make power. Trying to chug along at 3-4k rpm like the DMax isn't going to work with the 6.0.

Not sure what you consider "decent towing gears" behind a 6.2, but get any lower than what was commonly found under factory 3/4 and 1-ton trucks and you can't even run the speed limit with one.

4.10's at a minumum with a stick. 4.56's are better. OD will be needed to keep RPMs reasonable at highway speeds. 3.73's or 4.10's with a TH400's 2.48 1st and 1.48 2nd gear aren't going to work well. You also can't be afraid to spin the 6.2 when climbing a hill. It's power peak is at 3400rpm, so you gotta wind it up a bit tight if you want the goods from it

 

[camok5]

Anyone know what a mid 90's Ford 7.3 diesel gets for fuel mileage?

 

[rjfguitar]

Anyone know what a mid 90's Ford 7.3 diesel gets for fuel mileage?

Important....is it a '95-97 or '94?

Depends on the truck, but should get about 15 average.

 

[6.2Blazer]

I'm obviously not going to convince MaxPF otherwise, so go ahead and keep believing that two engines with the same HP rating will pull the same load up a grade at the same speed.

It's a good thing I don't have an engineering degree, or work at an automotive research facility, and that I don't work directly with engineers from both light and heavy truck manufacturers everyday. It's also a good thing I haven't owned a 6.2 truck for 13 years and I've never driven any other trucks pulling trailers.

 

[MaxPF]

You can lead a horse to water.....

Anyway, back to the OP's question, I think we all agree a 94-98 CTD Dodge would best serve his needs, and that a mid 90's Ford 7.3 or GM 6.5TD would work OK as well.

 

[Hogback Fabrication]

2. run engine "A" at twice the rpm as engine "B"
(assuming the torque curves per rpm were the same)

This is exactly what Max is saying. The gasser is probably capable of spinning twice the RPM that the diesel can and hence the same amount of work is performed.

 

[6.2Blazer]

This is exactly what Max is saying. The gasser is probably capable of spinning twice the RPM that the diesel can and hence the same amount of work is performed.

Think what you want, but for an example a 6.0L gas GM motor does not spin twice the RPM as the Duramax, and a 6.2 does not spin twice the RPM as a Cummins. I'm really starting to wonder if you guys have ever towed a trailer before. This is a pretty simply concept that is proven everyday in the real world.

MaxPF - Not sure what the "you can lead a horse to water" comment is all about, but I can see through all of the technical garbage you are throwing out pretty easy.

Regarding my comment about foot to the floor in 2nd gear, I was maybe running 4,500 rpm...the engine did not have the power to go higher. Sure, you could theoretically slightly lower the gearing to get to 5,500 rpm.. but the lower gearing pretty much cancels out the slight gain in engine rpm in regards to overall vehicle speed.

 

[Hogback Fabrication]

This argument is really getting mixed up between theory and the real world.

In theory, two engines of the same hp (regardless of torque) will be able to tow the same load up the same hill at the same speed if geared correctly. Period.

In the real world, the diesel (turbo ones, anyway) will make a joke of the gassers while towing (I did say that in a previous post).

 

[Mikey von]

I do not know the answer except that my low HP 6.2 feels better towing than my 5.3L did.

If your theory does not match up to real world testing, it is time to start wondering about your theory. Real world driving/testing/experiments do not somehow bend the laws of physics. Your theory must be incorrect.

 

[Hogback Fabrication]

Theories aren't wrong just because they don't always work in real life. That's why they're called "theories" . There are lots of variables that may make one truck pull better than another.

If anyone thinks horsepower doesn't matter, think of it this way:

Lets say I can put 200 pounds of force on a one foot lever attatched to the transmission input of a car (i.e. my force is replacing the force the motor would put out). That may be more torque than the cars engine could put out but I can't spin the transmission input very fast (maybe only a couple RPM). That sure as hell wouldn't move the car down the freeway at 80 mph. I can put out 200 ft.lbs. of torque but at only 3 RPM I am only worth ~1/10 of a horsepower and the car isn't going anywhere.

Engines aren't really capable of producing much torque, the reason they are useful is because they produce torque at high speeds. This allows you to use gear reduction to multiply the force output by the motor and put significant power to the ground.