You are correct here(sorry 95 dually). If you are at the same rpm and have more tq, you have to have more hp. 100% correct here. The point i was arguing is that my 5.4 has 70 more hp at 3500 rpm than my 7.3 has at 2k rpm, but my 7.3 will walk off and leave my 5.4 when both are hauling 10k lbs and i gun it at those rpms. And that's with my 5.4 in 3rd gear and my 7.3 in 4th(5.37 to 4.10 gearing advantage for the 5.4). So even with the gearing advantage and the 70 hp advantage it can't keep up. Why? Because it doesn't have the tq to keep the rpms up and the load moving.

For those that are saying gearing doesn't give it an advantage, that it just puts it in its powerband, look at it this way. Take two identical v10 trucks and hold them at 3500 rpm. They are going to be making the exact same hp and tq. Put them in some kind of space age tunnel that only allows air to go into the engine(to eliminate the wind resistance argument for the extra 5-10 mph). Give one truck 4.30's and the other 2.73's. Which one is going to accelerate faster when you floor them both at 3500 rpm? They are making the same exact power, turning the same exact rpm, have the same wind resistance, but one of them will snap your head back and the other will crawl like a turtle. That extra acceleration comes from the gearing, not the hp. That's why giving the v10 4.30's and letting it run in 3rd gear isn't a fair comparison to the 3.73 diesel in 5th gear.

 

But in your example, they are the EXACT SAME ENGINE with the EXACT SAME TRUCK with the EXACT SAME RPM.

That's not the same comparison as comparing a V10 and a PSD.

Your example should be about two engines, one that produces "X" mount of torque at 3500RPM, the other that produces 2*X torque at RPM/2 (twice the torque at half the RPM), and one is geared at 4:1, the other at 2:1.

They would accelerate at the same speed. Theoretically.

 

All this with a 4.10 rear end? Amazing...

If the trucks and loads weigh the same, and starting from the same speed the 7.3 walks away from the 5.4, I've got news for you: The 7.3 is making more horsepower at that moment.

Well, technically, they will produce zero torque, and thus zero HP, until you put a load on them.

They will NOT be making the same power. The truck with the 4.30's will be going considerably slower, and the driveshaft torque will be much lower, so the HP number will be lower, even though the engines are turning the same RPM. The 4.30 truck, going much slower, is doing much less work.

Yes, when you step on both of them, the 4.30 truck will accelerate faster, because the gearing advantage will allow substantially more rear-wheel torque to be generated, but ALSO because the engine is not yet operating anywhere near its horsepower capacity.

Say that both trucks weigh 7,000 lbs, and they are both going up a 5% grade, both are in 3rd gear (1:1) and we are still ignoring wind resistance:

Tractive force required for both trucks: 350 lbs. (amazing what ignoring wind resistance will do for you). Assuming a 33" tire, that would be 481 lb. ft. of torque at the axle. So:

2.73 truck:

3500 RPM / 2.73 = 1282 wheel RPM.
(1282*481) / 5252 = 117 RWHP.


4.30 truck:

3500 RPM / 4.3 = 814 wheel RPM
(814*481) / 5252 = 75 RWHP

The truck with the 2.73's is using 56% more horsepower!

Now since we're ignoring wind resistance, let's also ignore gearing losses. Thus we can transfer the rear-wheel HP directly to the crankshaft:

2.73 truck:

(117 HP * 5252) / 3500 RPM = 176 lb.ft.


4.30 truck:

(75 HP * 5252) / 3500 RPM = 113 lb.ft.

(Someone please check my math)

The slower truck is using less HP. When you stomp on the gas, it has more to spare, and will thus accelerate faster. Of course, the difference between the two trucks will become more and more noticeable the closer you get to the HP limit.

 

thats my point exactly. its the same truck, same rpm, same every last little detail except for gearing and one of them will out accelerate the other one and pull more weight. thats how much having better gearing can help you. all everyone(gassers) in here are arguing about is hp this and hp that. there is a lot more that goes into it than just hp. my point is that the better acceleration of the v10 or the ability to pull more weight(with 4.30's and in 3rd gear compared to 3.73's and 5th gear) was not due to just having more hp. youre giving it more hp AND a 2 to 1 gearing advantage. in my example one truck with the same hp would blow the other one off the road simply by having a 1.5 to 1 gearing advantage. so it cant be just about hp.

lets just use my truck(225 hp at 3k rpm) as an example to simplify it even more. take out every variable like wind resistance and all that. i am back on my infinite hill again and you are going to keep adding weight as i go up the hill until i bog down. do you think i can pull more weight up the hill in 5th gear(3.12 final drive ratio) at 3k rpm and 225 hp or in 2nd gear(9.72 final drive ratio) and 3k rpm and 225 hp? in theory(like gassers like), if i can maintain that 3k rpm i should be able to pull the same amount of weight since i am making the exact same power. but in reality(what diesel guys like), the more weight you add the more i am going to struggle to maintain the 3k rpm and i am going to bog down much faster. why? because i dont have the gearing to keep the rpms up and i am relying solely on hp to keep me moving. in 2nd gear i get to rely on both gearing and hp to keep my rpms up and keep me at my peak power. in my example that is the same hp and a 3 to 1 gearing advantage, but it will yield totally different results. thats the same advantage the gasser gets when you all give it its 3 to 1 gearing advantage "just to get it in its powerband."

 

ill be more than happy to run a tank out if you want to come along for a ride. all i ask is that you buy me a tank of fuel when i prove you wrong and buy me a nice steak dinner somewhere to make up the time i wasted proving it.

 

In my previous post above, I think I got the definition of the "grade" wrong, but you can still use the rear-wheel torque numbers regardless, since they're the same in both examples..

I wasn't challenging you or expecting to prove you wrong, just expressing amazement (and envy).

 

He was stating an average mileage for empty and towing, which I think 14 is a fair number to figure.

If you are consistantly getting 22 mpg you must be in the flat lands. My dad and I both had OBS psd w/ 3.55 rears and rarely saw 20. 18-19 was standard. You must be 2wd.

 

im not doing the same speed. there was maybe 10 mph difference(7.3 going faster, so more wind resistance according to the gassers). in my test i took an 8-9k lb trailer on a pretty good hill and got both to the start of their powerband. 4th gear and 2k for my 7.3 and 3rd gear and 3500 for my 5.4. i floored them and then watched what happened. the 5.4 could maintain speed but would not accelerate at all. the 7.3 had no problem hitting 5th gear and continuing to accelerate in 5th gear. i tried it with my 7.3 in 3rd gear too and it embarrassed the 5.4. thats why i did it in 4th the next time.

according to my numbers the 5.4 was making 232 hp at 3500 rpm and my 7.3 was making 162 hp at 2k rpm. at no point does my 7.3 make 232 hp, so it couldnt have been making more hp than my 5.4.

 

its a 1997 f250, regular cab, 4.10 gears, 5 speed and 4wd. and no, i dont live in the flatlands. i live in tennessee and do my driving all over southwest va, west virginia and tennessee. honestly, ive found that i get better mpg with 4.10's than i do with 3.55's. with 3.55's, at the same speeds, my rpms are much lower, so im having to fight the wind resistance while making less power. which means i have to run it harder to maintain speed or go up hills. which also means more downshifting. i just dont run the dog***** out of it and i keep it below or as close to 2k rpm as i can. im sure if i drove it like a stole it i could get it down in the 15's, but why would i want to?

a lot of people snicker when i tell them my mpg, so i assumed you were presenting me with a challenge anything i say on here, i dont have one problem backing it up to anyone that wants to come along for a ride. whether it be mpg or the ability of my 7.3 to outpull my 5.4 even though its making much less hp.

 

I think you are not even reading what I (and others) have posted, over and over again.

A truck of the same weight, going faster up the same hill, is PRODUCING MORE HORSEPOWER. Just do the numbers on rear-wheel HP for the two trucks, and then tell me where this extra HP came from, if your 7.3 can't produce it.

 

according to the dyno, at 2k rpm my 7.3 makes 162 hp and at 3500 rpm my 5.4 makes 232 hp. thats where im getting my numbers. whether im doing 20 or 120 at 2k rpm my 7.3 is making 162 hp(at the crank). you can do all those calculations with the gearing and forumulas and all that, but im going by actually driving the trucks. i can give you the numbers for my trucks(except speed, because i dont remember my mph's) if you want to run the numbers.

5.4 was turning 3500 rpm(232 hp and 350 tq) and was in 3rd gear(1.61 tranny ratio) with 4.10 rear end(6.6 final drive ratio).

7.3 was turning 2k rpm(162 hp and 425 tq) and was in 4th gear(1.0 tranny ratio) with 4.10 rear end(4.10 final drive ratio).

run the numbers on those and tell me what you get. what i get sitting in the seat is the 5.4 will not hit 4th gear and the 7.3 hits 5th no problem.

 

also, i am reading what you are posting. what i am saying is at the crank, at those two rpms, my 5.4 is making 70 more hp than my 7.3. thats a fact. not a theory or formula. but a fact. my 5.4 was in a lower gear and had the same rear end, so in theory it should be putting more hp to the ground than my 7.3. right? i understand the drivetrain and gearing loss to the rear wheels, but that shouldnt come into play here because the engine that is making more hp at the crank also has the gearing advantage. i could see your point if the higher hp engine at the crank had less gearing. like if i had the 5.4 in 4th gear with 2.73's at 3500 rpm and the 7.3 at 2k rpm in 3rd gear and 4.10's. but the 5.4 has the hp advantage at the crank AND the gearing advantage. but it still wont keep up.

both trucks also have the same size tires. 265/75 16's. both are regular cab long beds. i would say the weight is even too.

 

That is the problem with trying to figure out the difference all on paper. Real world results do not always equal the perfect world on paper.

 

OK, maybe someone can check my math. Using your numbers above, this is what I get:

On the 5.4, the rear wheels are turning 530 RPM, which is 49.9 MPH, and are producing 2308 ft.lb. of torque.

On the 7.3, the rear wheels are turning 488 rpm, which is 45.9 MPH, and are producing 1743 ft.lb. of torque.

Since you like to talk in terms of torque rather than HP, please explain to me how the 7.3 is producing 565 ft.lb. (24%) less rear-wheel torque at very close to the same speed, and can still out-accelerate the 5.4.

Truthfully, I don't doubt that your 7.3 is outpulling your 5.4, I just think the 5.4 is producing less horsepower than you think it is.

 

I checked your math and the only difference I have is the axle torque for the 5.4. I came up with 2310 vice 2308, but who's counting.

The only thing I would add is that you solved for axle torque and I would just add in tractive force so the tire size will be included. In this case, both tires are the same so it doesn't matter for comparison purposes but it does show the amount of force the tires are actually exerting on the ground to move the truck. In this scenario, I came up with 1,751 for the 5.4 and 1,321 for the 7.3.