Since Marty (rightfully) locked down the hijacked Horsepower thread, I thought I'd revive it in another thread as he suggested. So, here goes....
Ken,
Rob ol buddy your are confusing the hect out of yourself. You seem to think the formula is what we are burning not fuel.
I think you're arguing against something I'm not saying.
A internal combustion engine such as a diesel or gasoline motor or your heart operates by burning fuel. The amount of power it produces is a function of how much fuel it burns and how much energy is contained in that fuel.
I never disagreed with that. I only stated that fuel has no bearing on the relationship between torque and horsepower. Now the burning of fuel may well produce torque, but it ends there.
a diesel ... producer more TQ at a given RPM then a gasoline motor of the same displacement and operating pressure.
That's not necessarily true -- it depends on the RPM. A gasoline engine typically produces far more torque (and power) at 5000 RPM than a diesel does. But 5000 RPM is far from ideal for the typical towing application. Diesels produce more torque (and power) low in the RPM range. That's why they're typically better for towing.
If you have a gasoline motor you can equal the TQ of the diesel by increasing size, rpm, or operating pressure.
Increasing RPM does not (necessarily) increase torque. It increases power. Torque and power are not the same thing.
I'm glad you know the formula, but if you understood it better then you would realize that it just is a mathematical model of what I have been telling you.
I understand it well. But what you're telling me does not fit with the laws of physics. Your explanation intermixes the concepts of torque and power -- they are definitely NOT the same.
To move a bigger load you need more power/time.
No. You need more power, not power/time. Power is defined as work per time. Power/time is thus work per time per time, i.e. the time derivative of power. You may think I'm picking nits, but there's a big difference between power and the time derivative of power.
To get more power/time you got to turn the crank faster.
Again, no. To get more power (not power/time), you can either increase torque, or you can turn the crank faster (i.e. increase RPM).
To turn the crank faster you got to make it go boom more.
To turn the crank faster, you must apply torque. Note that I did not disagree that the application of this torque would require the burning of fuel, nor that more fuel burned would produce more torque, nor that a more efficient engine would produce more torque by burning the same amount of fuel. I simply said that torque is what turns the crank.
The burning of fuel produces torque. That torque induces an acceleration, which causes RPMs to rise. That, in turn, results in more horsepower. This cycle continues as long as the torque remains constant (or increases). But at some RPM, torque will begin to drop off. At that point, the RPMs will begin to build more slowly. Horsepower will still increase, but not as quickly. But as RPMs continue to increase, torque begins to drop off more rapidly. At some point, the dropoff in torque will be more than the associated increase in RPM -- this RPM is where maximum HP is reached.
-- Rob
* This post was
edited 01/13/05 05:08am by bimbert84 *
There you go again, looking at peak numbers. If only you'd learn to quit doing that, maybe we could discuss this more intelligently.
Well if people would stop the BS about about small block gas HP will tow the same as a Turbo diesel given the right gearing I will stop posting 345HP Hemi vs 325HP Cummins etc.
We can discuss this inteligently only if we can agree what is meant by "tow the same," or "tow better."
By "tow better," do you mean "accelerate faster"? That's probably what most of us mean. If so, no doubt the Cummins will win. Why? Because it has more torque (and thus more horsepower) in the low RPMs. When I pull away from a stoplight, I'm at low RPMs. Or when I'm in OD climbing a hill, I'm at low RPMs.
Or do you mean "pull load X at a faster top speed"? If so, the Hemi will win. Why? But at some point, high in the RPM band, that Cummins is going to run out of steam. It simply does not produce enough torque (and thus horsepower) that high in the RPM range to go any faster. The Hemi, however, has enough strength to keep going. It will take the Hemi a helluva lot longer to get up to speed, but at the top end, it's going to win out.
Rob,
I am giving you a challenge here. Get two drivers, take a hemi powered 3/4 ton Dodge and a Cummins powered 3/4 ton Dodge and hook 12,000 pounds to each of them and find a 7% grade (that should limit the top speed somewhat to almost legal speeds), start at the bottom at 65 mph with the trucks side by side and run them at full throttle to the top(at least 3 miles) and see which one gets there first. I know, you are going to use the wrong gearing excuse right? I think you will find a gear in there where you can run close to your horsepower peak rpm in the hemi if you try. Then report back with the results.
This will save a lot of theoretical BS and wasted time and tempers here on the forum that doesn't prove anything.
Oh, by the way, tests somewhat similar to this are done every day on roads across the country by owners of Cummins and Hemi powered pickups, and if you look at some past threads you might come up with the answer without having to do the test.
My grandfather always told me torque gets you moving, horsepower keeps you going. That's all I need to know. When I'm climbing up those hills a 4000RPMs I remember what Grampy said and say go little engine go!
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Ooooh no not this thread again.This has been beat do death with a stick.Do a search should have enough reading for a few days.
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My old 2000 4x4 7.3 235HP PSD Excursion towed my 41 ft TT great so do you think I should have gotten the 255HP 5.4 V8 instead and with 20 extra HP it should out tow the 235HP 7.3 PSD.
take a hemi powered 3/4 ton Dodge and a Cummins powered 3/4 ton Dodge and hook 12,000 pounds to each of them and find a 7% grade, start at the bottom at 65 mph with the trucks side by side and run them at full throttle to the top (at least 3 miles) and see which one gets there first.
I know, you are going to use the wrong gearing excuse right?
Not at all. Any meaningful comparison must assume all other things are equal, including the gearing.
But the problem here is that you're limiting the test to a fixed speed. That defeats the purpose. You have to let them go until they can't go any faster. That's what peak HP defines. The engine producing more HP, whichever one that is, will go faster at the top end. Note that it says nothing about how long it will take to get up to that speed!
The Hemi may not even be able to get up to peak HP in 3 miles. But it will get there eventually, and when it does, it will be moving faster than the Cummins. Note that is NOT the same thing as seeing which one gets to the top first! A 747 has a higher top speed than a dragster. Which one do you think would be the first to complete the quarter mile?
This will save a lot of theoretical BS and wasted time
The only problem with the theory is that many people interpret it to say something it doesn't. And that's precisely what happens in almost all of these HP/torque threads.
Torque defines rate of acceleration; HP defines top speed. You choose which is more important to you. For towing, I think it's fair to say rate of acceleration is more important than top speed. That's what makes the Cummins a better choice for that particular application.
My old 2000 4x4 7.3 235HP PSD Excursion towed my 41 ft TT great so do you think I should have gotten the 255HP 5.4 V8 instead and with 20 extra HP it should out tow the 235HP 7.3 PSD.
Why would I say that? There you go again, making up something that nobody said, and then arguing against it.
Quote: The Hemi may not even be able to get up to peak HP in 3 miles. But it will get there eventually, and when it does, it will be moving faster than the Cummins.
If you are running 65 mph at the bottom of a 7% grade just how much faster do you think you would be going 3 miles later at the top pulling 12,000 pounds? I think your hemi will probably reach its top speed much before it gets to the top.
'edited to put out the flames'
* This post was
edited 01/12/05 08:47am by JPhelps *
Watch yourself boys and girls, this could go sideways real quick too!
Keep the name calling/flaming etc to a minimum
Marty
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