DuraMax really 300hp?? and 520lb torque?

Lastly if TQ. is irrelevant, why do all of the manufactures quote it?

Torque is most certainly relevant. Anyone who tells you otherwise is blowing smoke. It's a major part of the horsepower equation.

The other part is rpm.

Torque by itself, without rpm, is pretty irrelevant, though, at least for evaluating performance. As is rpm without torque. Each one only tells half the story. So either one is meaningless without the other.

Don't believe me?

Do you want 2,626 ft/lbs of torque in your truck? In my very first example, I show you how to do it with a handheld electric drill motor. If torque by itself is meaningful, yank that Duramax and stick a drill motor in there.

Just be prepared to go reeeeeaaaal slow.

To have a meaningful number, you have to consider both the torque and the rpm it's made at.

The parameter that describes the combination of both torque, and the rpm it's made at, is called horsepower.

Within the context of the manufacturer's claims, a high torque rating means it's power is made with a combination of higher torque and lower rpm than other motors.

But, the fact that it's power is made with higher torque and lower rpm does not mean it can pull a trailer up a hill or accelerate faster than another truck with lower torque at higher rpm and the same horsepower.

Ultimately, the motor with the highest COMBINATION of torque and rpm (aka "horsepower") will put maximum torque to the rear wheels for any given speed. This is because more gear reduction can be applied to the lower torque/higher rpm motor and still get to the same ground speed. That extra gear reduction multiplies the lower torque and makes up for the deficit. Refer to the 6 facts above.

What's so cool about a high torque/low rpm motor is that it lasts a long time and it's fuel efficient. Not that at out-tows a properly geared low torque/high rpm motor of the same horsepower. It doesn't.

There, I did a whole post without any math.

Man, if someone doesn't get this by now, they probably never will.

[This message has been edited by ZFMax (edited 01-19-2002).]

I will probably get death threats for revisiting this topic, but I think this is a great post and it taught me a bunch!

There are just a couple of things I'm unclear on.

1. Does the manufacturer state the torque levels in a motor specifically to illustrate where in the RPM range (how low) the engine is making it's torque? This would support the low RPM / engine longevity argument well. Aside from that, I see no real benefit in publishing those numbers if gearing can mitigate nearly any engine's torque shortcomings. This question was addressed well by Hoot, I just want to see if I understand correctly.

2. What design characteristics does a diesel engine possess that enable it to produce gobs of torque at such low RPMs. (Rookie question)

3. If the max torque could be slid to the right along the RPM band, wouldn't you realize an exponential increase in HP? I realize this would lead to higher RPMs while towing, but moving the max torque up 1000 RPMs doesn't seem too excessive and would give you a substantial HP increase. What factors limit a diesel's ability to produce more torque 'up high'?

Thanks to ZFMax for the physics lesson! I guess I never really understood the proper relationship between HP & TQ (probably still don't!)

Kevin

[ 06-01-2002: Message edited by: 2K2AD ]</p>

Aaaaaaaaarrrrrrgggggghhhhh! I can't believe this topic has come back!

Oh well ...

1) I'm not certain about their motivations, although I wouldn't be surprised if they're not just a little bit taking advantage of people's misconceptions (which as we can see run rampant). What I know for sure is how to interpret the number ... when they advertise a high torque figure with a more modest power figure (i.e. our Duramaxes), they're saying it makes it's power with a combination of relatively high torque and low rpm. They may well be hoping people interpret a high torque figure as somehow meaning higher performance, which of course, it doesn't.

2) Now THAT'S a great question! I'm not a motor designer, but as I understand it, two things create torque in an engine: the combustion pressure and the mechanical advantage it has on the crank, aka stroke.

Diesels basically run on ping, which as I understand it, means the fuel doesn't so much burn as explode. And this explosion causes a lot of pressure, hence creating more torque. But, for reasons I don't fully understand, there are limits to how fast you can repeat this process (rpm), possibly related to heat? I'm not sure, someone on here probably knows.

3) Ah-ha, finally a question I can answer. You got it, Toyota. A good motor tuner looks at his torque curve, because he knows it's showing the cylinder fill. Various parameters of the motor are optimized for maximum cylinder fill at a certain rpm, for example, the intake tract length, the valve timing (in particular the intake valve close event), and the exhaust design. Changing these parameters such that the torque peak moves to the right is the whole idea when you're going for max power. Move the torque peak to the right and the horsepower comes up!

I think you understand this stuff good.

Oh hey, I heard a GREAT analogy awhile back about torque, rpm, and hp ...

horsepower is like your paycheck. Torque is your pay rate and rpm is the number of hours you work.

Just like it does you no good to have rpm without torque, it does no good to work 100 hours a week if you're only getting paid $1 an hour, right? Your paycheck (horsepower) is small.

Likewise, torque without rpm isn't useful. It does no good to make $100 per hour if you only work 1 hour a week, right? Your pay (horsepower) is small.

What matters is the COMBINATION of pay rate (torque) and hours worked (rpm). That's what gives you a fat paycheck (horsepower).

With a diesel, we get a good paycheck (300hp), and we manage to get it without putting in a lot of hours (rpm) because we make a good rate of pay (torque). Thus, we don't work ourselves to death. Gassers make good money too but they have to put in a bunch more hours than us to do it, hence they don't last as long.

Another good analogy is the hammer and nail. Say you've got 10 seconds to drive in a nail. You can do it with 10 whacks of a 1lb. hammer, at 1 second per whack. That's high rpm and low torque. Or you can do it with two whacks of a 5lb hammer at 5 seconds per whack. That's high torque and low rpm. Both are the same horsepower, they got the same amount of work done in the same amount of time.

[ 06-01-2002: Message edited by: ZFMax ]</p>

Now, how about a lesson on air density, power loss and turbos?

What great answers! I must have read parts of this post 50 times. Just when I thought I had a handle on it, someone would retort with what seemed like a valid contradiction.

I think I've got a good handle on it now. I'll second the misconception of the public part, before this post that is what I believed as well.

Thanks again!
Kevin

After reading about 12-15 post, I decided that if I were to learn something here I would have to read ZFMax post only. I think I learned a little.

I think my head hurts from reading all of the above ... but right now,I'm not even sure of that... called my wife to read these post (she's only taught high school physics for over 37 years (yes 37) and she says ZF seems to have a pretty good handle on things :confused:

Keep the posts coming!!!

This is my attempt at a record setting topic, almost 4 pages now.

What a Monday morning!!! I normally start out my work day reviewing the forums I frequent. Little did I know I'd stumble on this jewel and spend 4 count'em 4 hours going over it. Digging out the Machinery's Handbook and other sources, and pouring over notes I made to decipher the thread. So like it or not after that much time I'm gonna post!!!!!

ZFMAX, you did a good job with the torque vs horsepower comparision. I spent 7 years in the industrial clutch and brake field and this made me dust off stuff I haven't used for a couple years.

Thanks for the positive comments, guys, I appreciate it.

Sorry, I don't really know the answer to the question on turbo's and altitude. I would *guess* that it depends on whether the wastegate operates on relative or absolute pressure, but that's just a guess. There's probably more to the story.

I must be living right, I filled my truck at lunchtime today and got a new high, 19.9mpg, and yes, I topped it off good. I haven't seen 19's since I first got the truck last fall, all winter long it was 17's with a few 18's popping up this spring. Not sure if I just got a great tank of fuel or if the motor just likes hot weather, this last tank was run through with temps in the 90's.

My squeaky clutch pedal is fixed, the 900rpm vibration noise is fixed, and the SES light from using the block heater is fixed (not that I use the block heater this time of the year). If I can just get that !@#$% steering rattle fixed, I'll be in truck heaven.

Speaking of which, stopped by the Ford dealer today to pick up some parts for the wife's Expedition. Looking at a new F350 on my way out, a salesman approached. Did you know they have an 18% failure rate on Duramax engines? Yepsiree, they break left and right. At least a couple hundred folks have brought their Duramaxes in, BEGGING the Ford dealer to take'em in trade, they're so bad! Unbelievable. This sales guy claimed 34 years in the business, he's "in-the-know"! 'Course, when I asked him the GCWR on the F350 I was looking at, he proceeded to describe GVWR. "No, GCWR", says I. "Never heard of it, I don't think Ford rates that." Uh-huh. I found it in his book and showed it to him. 34 years in the business, what an expert. 20K in case anyone cares.

[ 06-03-2002: Message edited by: ZFMax ]</p>

My air density/turbo comment was kinda leaning towards comparing gas engines to diesels. I agree that horsepower is horsepower, but in a gasser horsepower can drop significantly with altitude AND temperature. So, before anyone thinks a 6.0 (or even 8.1) might whip a Duramax--that would be at sea level on a cool day.

So you're saying the wastegate works on absolute pressure? Instead of pressure relative to the current atmospheric pressure?

If it works relative to the current atmospheric pressure, the real boost pressure will drop with altitude, and therefore, uncorrected horsepower will drop as well. But, it may well work on absolute pressure as you say, I'm not denying that, I honestly don't know.

It'd be interesting to dyno one of these trucks at sea level and then at altitude and see the difference.

Okay, here's my hat. (don't make me eat it)

I just spent a ton of time figuring out dyno's, HP, torque, RPM, gearing and on and on. Here's what I can tell you about what I've learned.

There are basicly two types of dynos. Inertial and retarder (brake type).

When you use an inertial dyno to measure power, you are using a given rotational mass and accellerating it (Dynojet). Based on the accelleration curve, speed of the drum, time, and mass of the drum you can calculate HP. It takes a certain amount of work (HP) to move that mass. This type of test measures HP only and torque is calculated based on the above formula (HP=T*S/5252).

Then there is a brake (retarder) dyno. There are several types of brakes and it really doesn't matter what type of brake it is (unless you really want to split hairs). These dynos are used by labs, engine builders, manufacturers, etc. The reason being that the control conditions can be duplicated quite accurately. Not to mention, it gives a more ture reading of an engine's performance.
The way they work is that an engine is brought to a given speed and held there. Then the brake is used to put load on the engine until the engine starts to lose against the brake (full throttle on the engine at that speed). The brake requires a certain amount of force to resist the engine. That force causes the brake to deflect (Torque). There is a strain gauge that measures the amount of deflection of the brake. This deflection is converted to ft-lbs. You take these data points and plot them and voila, you have your graph.
Now in this dyno, torque is measured. But you have RPM so you can calculate HP. Typically, the dyno run consists of running the engine up to the governor and bringing the engine down with the brake and then allowing it to come back up to the governor taking data readings on the way back up.

Now advertised readings for an engine are usually taken at the flywheel (as measured by the latter dyno). The Dmax gives 300 HP and 520 ft-lbs as peaks. Being that torque is a measure of force, torque is usually stable through the drive train (give or take). You can multiply this force with gearing as was stated above. The drivetrain takes a certain amount of work to function (approximately 20% but that varies widely). I heard around 60 HP for the Dmax. So a HP reading at the rear wheels for a stock D/A should be around 240 HP. I think this is reasonable.

As for the gearing to match performance between gassers and diesels. It's not really gonna happen. The reason being that, you can only modify torque through gearing. HP won't change. If you raise the torque by gearing, you will lower speed (RPM) proportionately. That means that HP will be constant. The benefit of a diesel over a gasser is that it takes less RPM to make the same amount of HP that a gasser can. That means that torque (force the engine can make) is higher.
Torque is what makes the truck move. HP is how fast it can move it. For example, a gasser and a diesel with the same HP ratings (gearing, tranny, everything being the same) will take the same amount of weight and move it the same distane (or to the same ultimate speed). A diesel, because of it's torque, will do it faster (or get to it's ultimate speed faster).

I surely hope that I didn't muddy the waters any. If I did, sorry. If you have more questions, or if I wasn't really clear about something (it happens), post it and lemme know. I'll try to explain it better.

Okay, here's my hat. (don't make me eat it)

I just spent a ton of time figuring out dyno's, HP, torque, RPM, gearing and on and on. Here's what I can tell you about what I've learned.

There are basicly two types of dynos. Inertial and retarder (brake type).

When you use an inertial dyno to measure power, you are using a given rotational mass and accellerating it (Dynojet). Based on the accelleration curve, speed of the drum, time, and mass of the drum you can calculate HP. It takes a certain amount of work (HP) to move that mass. This type of test measures HP only and torque is calculated based on the above formula (HP=T*S/5252).

Then there is a brake (retarder) dyno. There are several types of brakes and it really doesn't matter what type of brake it is (unless you really want to split hairs). These dynos are used by labs, engine builders, manufacturers, etc. The reason being that the control conditions can be duplicated quite accurately. Not to mention, it gives a more ture reading of an engine's performance.
The way they work is that an engine is brought to a given speed and held there. Then the brake is used to put load on the engine until the engine starts to lose against the brake (full throttle on the engine at that speed). The brake requires a certain amount of force to resist the engine. That force causes the brake to deflect (Torque). There is a strain gauge that measures the amount of deflection of the brake. This deflection is converted to ft-lbs. You take these data points and plot them and voila, you have your graph.
Now in this dyno, torque is measured. But you have RPM so you can calculate HP. Typically, the dyno run consists of running the engine up to the governor and bringing the engine down with the brake and then allowing it to come back up to the governor taking data readings on the way back up.

Now advertised readings for an engine are usually taken at the flywheel (as measured by the latter dyno). The Dmax gives 300 HP and 520 ft-lbs as peaks. Being that torque is a measure of force, torque is usually stable through the drive train (give or take). You can multiply this force with gearing as was stated above. The drivetrain takes a certain amount of work to function (approximately 20% but that varies widely). I heard around 60 HP for the Dmax. So a HP reading at the rear wheels for a stock D/A should be around 240 HP. I think this is reasonable.

As for the gearing to match performance between gassers and diesels. It's not really gonna happen. The reason being that, you can only modify torque through gearing. HP won't change. If you raise the torque by gearing, you will lower speed (RPM) proportionately. That means that HP will be constant. The benefit of a diesel over a gasser is that it takes less RPM to make the same amount of HP that a gasser can. That means that torque (force the engine can make) is higher.
Torque is what makes the truck move. HP is how fast it can move it. For example, a gasser and a diesel with the same HP ratings (gearing, tranny, everything being the same) will take the same amount of weight and move it the same distane (or to the same ultimate speed). A diesel, because of it's torque, will do it faster (or get to it's ultimate speed faster).

I surely hope that I didn't muddy the waters any. If I did, sorry. If you have more questions, or if I wasn't really clear about something (it happens), post it and lemme know. I'll try to explain it better.

I would like to thank everyone who has posted under this thread. The effort to provide extended technical information in a manner that can be understood by all commendable. A greater understanding of torque vs. horsepower and how the figures are developed has been rewarding to all. Unfortunately, I am just not that mechanically inclined. I will remember the basics though:
1. Press with right foot and go.
2. With diesel press right foot and tow.

Thanks for all the hard work. [img]smile.gif[/img]

Philip

Amianthus: OK, you invited questions, I'm gonna lay'em on ya ...


&gt;&gt;&gt;&gt;Being that torque is a measure of force, torque is usually stable through the drive train (give or
take).&lt;&lt;&lt;&lt;

At ANY point in the powertrain, anywhere you select, the formula hp = (torque x rpm) / 5252 has to apply, right? Crank, inside the tranny, driveline, rear wheels, whatever, that relationship between horsepower, torque, and rpm is always true, for any rotating shaft. The formula defines it that way.

So if drivetrain losses are eating horsepower, don't they also have to eat torque and/or rpm? How can I keep torque and rpm the same and have less horsepower?


&gt;&gt;&gt;&gt;Torque is what makes the truck move.&lt;&lt;&lt;&lt;

Is it torque at the engine that makes the truck move? Or torque at the rear wheels?

If it's torque at the rear wheels, doesn't gear reduction between the engine and the rear wheels affect that number?

If the engine's rpm is higher, can't more gear reduction be applied for a given rear wheel speed?

If more gear reduction is applied, doesn't that increase the torque at the rear wheels?

Ultimately, doesn't the highest *combination* of torque and rpm at the engine determine the torque at the rear wheels for any given speed?

Isn't the *combination* of torque and rpm called "horsepower"?


&gt;&gt;&gt;&gt;A diesel, because of it's torque, will do it faster (or get to it's ultimate speed faster).&lt;&lt;&lt;&lt;

Wait, doesn't the highest rear wheel torque accelerate the fastest?

And didn't we just show that highest rear wheel torque at any speed come from the highest combination of torque and rpm (horsepower) at the engine?

So let's say I've got two trucks side by side, one a torquey diesel, the other a peaky gasser. Both are the same weight and have the same size tires Both are at full throttle and making 300hp and going the same speed. The diesel has a whole bunch more torque than the gasser.

Which will accelerate faster?

Both have 300hp at the rear axle, right? And they're going the same speed, right? So the rear wheel rpm is the same, right?

Well, if the hp at the rear wheels is the same, and the rpm at the rear wheels is the same, doesn't the torque at the rear wheels have to be the same, too? Doesn't the formula say so?

So why would the diesel accelerate faster?

[ 06-05-2002: Message edited by: ZFMax ]</p>

Quote:

---

&gt;&gt;&gt;&gt;Being that torque is a measure of force, torque is usually stable through the drive train (give or
take).&lt;&lt;&lt;&lt;

At ANY point in the powertrain, anywhere you select, the formula hp = (torque x rpm) / 5252 has to apply, right? Crank, inside the tranny, driveline, rear wheels, whatever, that relationship between horsepower, torque, and rpm is always true, for any rotating shaft. The formula defines it that way.

So if drivetrain losses are eating horsepower, don't they also have to eat torque and/or rpm? How can I keep torque and rpm the same and have less horsepower?

---

That's a very good question. Yes, you will lose torque as based on that equation which applies throughout the driveline. I should've chosen my wording a little better. Actually, I don't know what I was thinking. You are right on this point. Drivetrain losses amount to around 20%. Now this varies from vehicle to vehicle, and there is a super complicated formula that will allow you to accurately determine driveline losses. But I just stick with 20%.

Quote:

---

&gt;&gt;&gt;&gt;Torque is what makes the truck move.&lt;&lt;&lt;&lt;

Is it torque at the engine that makes the truck move? Or torque at the rear wheels?

If it's torque at the rear wheels, doesn't gear reduction between the engine and the rear wheels affect that number?

---

Torque at the engine is what makes the truck move. Yes, gear reduction does affect torque at the rear wheels. So does OD in your transmission. What also comes into play is wheel speed (RPM). If you take the torque at the rear wheels and the rpm of the rear wheels, you can calculate HP. You will see that a 3.0 rear will have the same HP as a 6.0 rear end ratio. The 3.0 will spin faster and thus have less torque to the ground. The 6.0 will have greater torque but spin slower. They will both have the same HP (all other things being equal).

Quote:

---

If the engine's rpm is higher, can't more gear reduction be applied for a given rear wheel speed?

If more gear reduction is applied, doesn't that increase the torque at the rear wheels?

Ultimately, doesn't the highest *combination* of torque and rpm at the engine determine the torque at the rear wheels for any given speed?

Isn't the *combination* of torque and rpm called "horsepower"?

---

Yes. More torque would be made, but at the sacrifice of wheel speed (RPM). RPM is independent of torque.
So no. Combinations only apply when HP is being calculated. We are assuming that HP is a constant in this discussion (aren't we?).
Yes, the combination is used to determine HP.

Quote:

---

&gt;&gt;&gt;&gt;A diesel, because of it's torque, will do it faster (or get to it's ultimate speed faster).&lt;&lt;&lt;&lt;

Wait, doesn't the highest rear wheel torque accelerate the fastest?

And didn't we just show that highest rear wheel torque at any speed come from the highest combination of torque and rpm (horsepower) at the engine?

So let's say I've got two trucks side by side, one a torquey diesel, the other a peaky gasser. Both are the same weight and have the same size tires Both are at full throttle and making 300hp and going the same speed. The diesel has a whole bunch more torque than the gasser.

Which will accelerate faster?

Both have 300hp at the rear axle, right? And they're going the same speed, right? So the rear wheel rpm is the same, right?

Well, if the hp at the rear wheels is the same, and the rpm at the rear wheels is the same, doesn't the torque at the rear wheels have to be the same, too? Doesn't the formula say so?

So why would the diesel accelerate faster?

---

That's a very good question. After looking at my post, I realized that I should've chosen my wording much better (again, don't know what I was thinking). I should've stated that a diesel will get to it's peak HP faster than a gasser. That would've been more accurate.

It goes like this. The diesel makes it's peak HP at about 2700 RPM (mine, not yours). So I hit peak HP pretty fast. Where a gasser hit's it's peak HP at around 4500 RPM. It would take the gasser longer to hit peak HP because it has less torque. In this example, my diesel would be making 584 ft-lbs torque at peak HP. The gasser would be making 350 ft-lbs at it's peak HP. So for the same amount of HP, the diesel makes more force to move it's load.
Now assuming a 1:1 transmission in both and a 1:1 rear end in both, the diesel would be only turning the wheels at 2700 RPM at peak HP. That's not nearly as fast as the gasser that will turn it's wheels at 4500 RPM. The diesel just gets there faster. If you were to leave the diesel alone and give the gasser a 1:1.66 ratio, the gasser and the diesel would have the same wheel speed and torque. The engines would be the same, but the gear reduction would equalize the performance between the two.
The statement you made about the HP, and wheel speed being the same therefore torque would be the same is not quite right. RPM wouldn't be the same. It couldn't because the RPM at which both engines make peak HP are different.

The diesel accelrates faster because it hit's it's peak HP faster. Because of more torque for a given RPM. Yes, gear reduction will help the gasser with torque at the sacrifice of wheel speed (RPM).

The biggest benefit to the diesel is it's torque. We know this. This is the force that is generated by the engine (not the work). If it takes 250 ft-lbs to move the load, then both would be able to handle the work (although the gasser would be working harder to maintain it). Then you encounter a hill and it now takes 400 ft-lbs to keep the load moving. The diesel will be able to resist slowing down more efficiently than the gasser, because now the gasser engine has to slow down until it hits an equilibrium RPM when torque matches 400. Downshifting will help accomplish this, but you sacrifice speed. But the diesel can still move the load as it does not have to downshift because the available torque to move the load is higher than is required at 300 HP.

I hope this cleaned things up a little. If you have more questions (or catch another bad choice of wording), post it.

Sigh. Okay, Let's try again.

&gt;&gt;&gt;&gt;Torque at the engine is what makes the truck move&lt;&lt;&lt;&lt;

'Scuse me? You're saying the torque at the engine is more significant for making the truck move than the torque at the rear wheels? Seriously?

So why do we need all these gears in our tranny and rear axle? I mean, if that engine number is all that matters, why do we try so hard to change it before it gets to the rear wheels?

&gt;&gt;&gt;&gt; Yes. More torque would be made, but at the sacrifice of wheel speed (RPM). RPM is independent of torque. So no. Combinations only apply when HP is being calculated. We are assuming that HP is a constant in this discussion (aren't we?).&lt;&lt;&lt;&lt;

You missed where I said "at any given speed".

Look, this is really a very simple concept. Let's take an example.

We have a diesel that's turning 2000rpm and making 400ft/lbs of torque. That's 152hp, right?

We have a gasser that's turning 4000rpm and making 200ft/lbs of torque. Again, that's 152hp, right?

Let's say we gear the diesel 5:1 overall (trans x rear end). Therefore, the rear wheels are turning 400 rpm, right? 2000rpm divided by 5 = 400rpm. What's more, the rear wheels have got 2000ft/lbs of torque, right? 400ft/lbs times 5 = 2000ft/lbs, right?

Let's say we gear the gasser 10:1 overall (trans x rear end). Therefore, the rear wheels are turning 400 rpm, right? 4000rpm divided by 10 = 400rpm. What's more, the rear wheels have got 2000ft/lbs of torque, right? 200ft/lbs times 10 = 2000ft/lbs, right?

So both of these trucks are going the exact same speed (400 rear wheel rpm) and have the exact same torque at the rear wheels (2000 ft/lbs) right? Assuming they're the same weight, and have the same size tires, the acceleration has to be identical, right? I mean, f=ma, that's the first thing they teach you in physics.

So if performance is identical, what in the world does it matter, performance-wise, whether the motor is making 400ft/lbs or 200ft/lbs?

Answer: it doesn't. What the gasser lacks in engine torque, it makes up for in engine rpm. Because it has more rpm, it can be geared deeper and still be going the SAME GROUND SPEED. The driver can be running a gear or two lower, or the rear end may have a shorter ratio, or some combination thereof, but the fact is, at any given ground speed, if it's making the same horsepower, it'll have the same torque at the rear wheels, regardless of the fact that it's only got half the torque at the engine.

&gt;&gt;&gt;&gt;I should've stated that a diesel will get to it's peak HP faster than a gasser. That would've been more accurate.&lt;&lt;&lt;&lt;

&gt;&gt;&gt;&gt;It goes like this. The diesel makes it's peak HP at about 2700 RPM (mine, not yours). So I hit peak HP pretty fast. Where a gasser hit's it's peak HP at around 4500 RPM. It would take the gasser longer to hit peak HP because it has less torque. In this example, my diesel would be making 584 ft-lbs torque at peak HP. The gasser would be making 350 ft-lbs at it's peak HP. So for the same amount of HP, the diesel makes more force to move it's load.Now assuming a 1:1 transmission in both and a 1:1 rear end in both, the diesel would be only turning the wheels at 2700 RPM at peak HP.&lt;&lt;&lt;&lt;

The problem with that example is you're talking about the same gearing for two motors that are running at radically different rpms, and therefore the trucks are running at radically different speeds. You're not looking at gearing as something that can (and should) be different between a gasser and a diesel. Basically what you're saying is "hey, if I gear them the same, the diesel accelerates more quickly to a lower speed!" Yeah, so?

That's totally meaningless. My truck accelerates a whole bunch quicker in first to a lower speed than it does in 6th to a higher speed, too. So what? If anything, that makes my point. It's EASY to get rear wheel torque and accelerate quickly. Just put it in first. It's EASY to get rear wheel rpm and go real fast. Just put it in 6th. What's tough is to get both at the same time. As you gear for more rear wheel speed, the rear wheel torque drops. As you gear for more rear wheel torque, the rear wheel speed drops. Ultimately, what matters is how much of BOTH rpm and torque you can get at the same time. The combination. That's called horsepower.

This is EXACTLY why I've done all of my examples "at any given speed", something you seem to have overlooked. Unless you equalize the speeds through gearing, comparisons of torque to the rear wheels are meaningless. Yeah, sure, geared the same, the diesel delivers more torque to the rear wheels at a slower speed. So what? Take a gasser of the same horsepower, gear it to go that SAME SPEED, and it's gonna put just as much torque to the rear wheels! That's a fact, not an opinion.

&gt;&gt;&gt;&gt;The statement you made about the HP, and wheel speed being the same therefore torque would be the same is not quite right. RPM wouldn't be the same. It couldn't because the RPM at which both engines make peak HP are different.&lt;&lt;&lt;&lt;

See, you missed where I said "and going the same speed". With two different engine rpms, that implies they're geared differently. You've got to start looking at gearing as a variable, not a constant. It's very simple to change your gearing by just moving the shift lever. And of course, you can get a gasser with a shorter rear end.

&gt;&gt;&gt;&gt;The biggest benefit to the diesel is it's torque. We know this.&lt;&lt;&lt;&lt;

I know it, too. But I also know it's not a performance metric. It's an adjective that describes how the performance metric (horsepower) is provided. A high torque figure means the engine's horsepower is made with relatively low rpm. It doesn't somehow make my 300hp stronger than someone else's 300hp that's made with low torque and high rpm. Both will put the same torque to the rear wheels when geared for any given speed. The formula says so. If the rear wheels in both trucks have the same horsepower, and they've been geared to go the same speed, they MUST have the same torque. That was the point of the example in my previous post. There's no way around it, if you're going to follow the formula.

&gt;&gt;&gt;&gt;This is the force that is generated by the engine (not the work). If it takes 250 ft-lbs to move the load, then both would be able to handle the work (although the gasser would be working harder to maintain it). Then you encounter a hill and it now takes 400 ft-lbs to keep the load moving. The diesel will be able to resist slowing down more efficiently than the gasser, because now the gasser engine has to slow down until it hits an equilibrium RPM when torque matches 400. Downshifting will help accomplish this, but you sacrifice speed. But the diesel can still move the load as it does not have to downshift because the available torque to move the load is higher than is required at 300 HP.&lt;&lt;&lt;&lt;

You absolutely, completely, totally ignored the difference in engine rpm and gear reduction between the two trucks in that example.

The engine torque is totally irrelevant for determining whether the truck slowed down for that hill or not. All that matters is whether or not enough torque was reaching the rear wheels.

If those two trucks are making the same horsepower, and both are running the same speed (a difference in gearing is implied there), then they've got the same torque at the rear wheels. And therefore they will react to the hill in exactly the same way. The difference in torque at the engine has absolutely zero to do with anything.

In summary, you (and others who are confused about this) are trying to add way too much significance to the engine's torque figure with respect to performance. You understand that torque moves the truck, so you're immediately trying to draw a direct connection between engine torque by itself and performance. But there isn't any. Zero. Zilch. Nada. Why? Because it's rear wheel torque that moves the truck, not engine torque. And that's a hugely important distinction. You can't just gloss over it, you have to understand it. You can't go making up examples that ignore it, they're meaningless.

The engine's torque figure is nothing more than an adjective for it's horsepower. It's a number that's telling you that the engine's horsepower is made of high torque and low rpm, that's all. But gearing (trans and rear end) is all about taking whatever torque and rpm combination the engine provides and converting it into the torque and rpm makeup we need at the rear wheels. So the makeup at the motor is not significant for performance, we can easily convert it to whatever makeup we need. Only the total combination of torque and rpm really matters for performance. That's why we talk in horsepower when we're talking about performance.

If we had no gearing in between the engine and rear wheels, I would agree completely, the torque & rpm makeup of the engine's horsepower would be hugely significant for performance.

[ 06-06-2002: Message edited by: ZFMax ]</p>

With all the laws of physics flying around here about horsepower, gearing, RPM, torque, etc., where does rotational mass come in to play???

You could take a 300 Horsepower V-8 Lexus engine and stick it in the Kenworth, compute all the rpm's, gear ratios, etc. and still not pull a sick wh-re off a p!ss pot!

Your numbers might all add up (fuzzy math), but you are still leaving some things out of the equation.

Any of you old enough to remember the 'poppin John' John Deeres. Wasn't a whole lot of HP, RPM, etc., but sure was a whole lot of rotational mass.

[ 06-06-2002: Message edited by: Jumbo Jet ]</p>