This may not be the best explanation, but I'll take a stab at it. And hopefully I won't say anything completly wrong. I will explain with a gas engine. A diesel would be different in how its throttled, but with similar results.

Obviously, a truck on level ground requires less power to move at a given speed than the same truck on a 10% grade, yet it can maintain the same speed in the same gear at both times (unloaded, in this case). The same engine at the same rpm has to be able to produce different levels of power. For a gas engine, this is done with the throttle. A gas engine needs to run at an approximately stoichiometric ratio of mass of air to mass of fuel. For every ~14.7 lbs of air into the engine, you need ~1 lb of fuel.

You control the amount of air going into the engine with the accelerator, which opens and closes the throttle plate. The engine then, by computer controlled injectors, adjusts the fuel to match the air flow. If the throttle is not fully open, then engine cannot pull in enough air to "fill" the cylinders. Air, being a gas, will naturally fill the cylinders, just at a lower pressure. The mass of air that the engine could contain is less than it could hold at atmospheric pressure. This is known as the volumetric efficiency of the engine, and, for a given engine, it varies with both throttle opening and engine rpm. Under part throttle cruise, volumetric efficiency will be much less than 100% (I think my car is in the mid 30's), while at WOT it can exceed 100%.

Since the mass of air flowing through the engine varies, so does the amount of fuel burned. And with less fuel burned, less power is generated.

Clear as mud?

 

I was just describing a fuel load. My theroy at this point is. A engine is rated by a x output at a y rpm. Period. That's the max the engine can produce no matter how much fuel you give or rpm. Right? Youbuild the output until peak at a give rpm then after that your just building speed. I do not understand whst the fuelload has to do with it as long as its enough to get you to that peak.
So say I finally understand. Aight then just as you said only using a percentage of peak output. I'll buy that but, same percentage or close at different peak outputs = different outputs. Yes/ no?
So I'm am to take it that if where to put 2 same SDs on a dyno w/ different engines and you add weights to the lighter engine SD and you put em on cruise at 65 mph both trucks is going to show same output numbers? I've been googling this for an hour and can't find a dyno chart like this. I've even tried finding dyno results of just running at hyway rpms w/ no luck.

 

Yes if you take two different engines and place the same load on them they will show the same power at the same load conditions if all you are doing is holding that load at a constant. I doubt you will ever find a dyno curve showing this. It takes "X" amount of power to move a said load at 65 mph. It doesn't matter what the engine is, the amount of power required is the same. Where the difference lies is how much power each engine holds in reserve that can be called upon when needed whether it be pulling out to pass or climbing a hill.

 

ugh. . .you cant find a dyno chart for this because no1 conducts "highway load" dyno runs. 1) cuz no1 cares, and 2) the amount of research needed to accurately conduct such an experiment would not be worth the trouble. you'd have to take into account air resistance, drag, drivetrain load, tire size, gear size, grade, and much more to determine the load to place on the dyno (yikes).

you could, on the other hand, monitor your throttle position (in % of WOT), and do dyno runs that way. it would give you an idea of relationship between the skinny pedal and power production. but again, im not sure if anyone who's done this cares to post up his results on the internet. not to mention max rpm requires 100% throttle, so you'd be conducting dyno runs with considerably less rpm as a redline.

 

this here's clear as drinking water.

 

Funny part, I still remember old car add saying that it takes 8HP to push compact car at 50 mph. YES >>>> EIGHT PONIES.
So it takes probably 30 to push Superduty at highway speeds. All excess power is for acceleration and hill climbing.

 

You're right, HP and watt ARE the same. The HP is the number you should pay attention to, because it incorporates both torque and speed, and is the true measure of the truck's ability.

Engine torque is indeed, to some extent, a ploy. Yes, it tells you a little something about how the truck will behave under load, but the torque number alone tells you nothing about the ultimate ability of the truck. Not enough information.

 

It certainly can, if it's got the right gears.


No. When you get to the hill and add throttle, while the wheel RPM remains the same, the rear-wheel torque goes up. Power is speed times torque. The speed remained the same, but the torque went up, so you are putting more power to the ground. And, of course, your engine is producing more HP.

 

An engine with 100ft/lbs of torque, and 1000HP would run at 52520 RPM. Yes, 52,520 RPM.

 

the same thing could be said about hp (it being a ploy). . .and neither, by themselves, tells the entire story (if anything). . .

a 500 hp semi motor (somethin akin to 14-15 liters) generally has anywhere between 1500-2000 lb/ft of torque (stock. . .the amount after mods is immense[3-3500 lb/ft]). any one of us can match the 500 horse. . .and 1000 lb/ft is easily attainable with any diesel in a 3/4 ton. . .but the semi motor has the capability of towing loads that would be laughable for our trucks at 500/1000. . .or 1000/1000 for you heavily modded gassers out there lookin to have 1000 lb/ft worth of towing capability. the reason the hp is so low, is cuz the rpm is low also. yes, torque can be used as a measurement of performance. in fact, its needed in most instances to calculate hp. . .

you can guestimate, rather accurately, a motors displacement and max rpm from its hp/tq numbers. in turn, you could guestimate its "ability" to do work (basically for which application the motor would perform optimally[car,truck,drag racer,etc]). if you only have a torque value, or only have a hp value, not much can be said.

 

What?

 

yep, what hes saying is that a theoretical 50cc motor that can capably (breath) spin to 52,525 rpm can make 1000 hp. . . .meanwhile guzzing as much fuel as his truck would at 1000 hp

 

Assuming that 100ft/lbs and 1000HP happens at the same RPM.

HP=Torque*RPM/5252

So, if HP=1000, and torque=100,

1000*5252=Torque*RPM
5252000=100*RPM
52520=RPM.

 

At least mine isn't wrapped in a Dodge...

 

you dont think im a dodge fan do you? just went for the strongest components available (none of which are dodge). . . .and yes its a shame its all wrapped in (what inevitably will be) a leaky, rusty, dodge body with an underpowered steering box.