500 HP is 500 HP. If a semi engine is only capable of 500 HP, you will never get more than 500 HP to the ground, in any gear, and regardless of the engine torque number. Every notice how semis slow WAY down on hills? It's because they are limited by horsepower.

If any other engine (PSD, V10, etc) is TRULY capable of 500 HP, and you have the RIGHT GEARS, it can move the same load at the same speed that the 500 HP semi motor can. Of course there are lots of reasons you wouldn't want to do this, longevity, efficiency, etc.

Torque is needed in ALL instances to calculate HP, you can't determine HP without knowing the torque value:

power = speed x torque

 

what is the speed variable youre talkin bout? cant say ive ever seen the hp equation quite put like that. . .since "speed" isnt defined. . .

hp=(torque x engine rpm)/5252 is the only one i know of. . .dunno how you would replace "speed" in your equation to yield the same values as this equation. . .

 

I'm even going to ask how you came to this logic. I use both numbers. I understand what both values mean. If I can only know 1 value then I want the tq. That's the work force. I like to know the hp cause that tells me how effective the workforce is. You can use tq values to find hp and hp values to find tq value.
Guys I understand how the induction works. I understand how the accelerator works. I just don't understand why the throttle has to be @ WOT to for peak output at 2200rpms. It doesn't take WOT to reach that rpm. It isn't twisting it any harder. More fuel raises the rpms to get more speed. I reckon its not for me to understand.

 

lol itll click one day. . .

 

this is just the first dyno chart that came up on google. . .now, these lines in the graph represent the MOST AVAILABLE POWER at the test-range rpm via WOT (IT WOULD BE IMPOSSIBLE TO ACHIEVE THESE NUMBERS WITHOUT WOT). just because your at that rpm, doesnt mean youre producing that amount of power. imagine going down a hill, or downshifting using the motor to slow you down. at 2500 rpm, no throttle, there is no hp being produced by your motor (excluding "braking hp" from the example). . . .likewise, it would take a little fuel (a little hp) to turn the motor, drive components, and keep the weight of bike moving along at 2500 rpm and a steady speed. that bein said, the power to do that is somewhere between 0 (no fuel/throttle, slowing down) and the peak numbers (acceleration). on this graph it looks like it would be a little more than 40hp available. so, somewhere between 0 and 40 is what it takes to keep this thing movin steady at 2500 rpm. remember, the 40hp @ 2500 is a representation of how much hp is available at that rpm, but not what is always used. . .in order to access the 40 hp the rider of this bike would have to twist the throttle all the way (WOT). in other words, the throttle represents the amount of power you are demanding at 2500 rpm. yes, the rpm will continue to rise and so will your available power. . . but without holding the throttle wide open, those numbers will not be achieved.

 

By speed, I mean RPM. It doesn't have to be just engine RPM, you can calculate rear-wheel HP if you know rear-wheel torque and rear-wheel RPM. And rear-wheel HP = engine HP minus drivetrain loss, which is another reason HP is a better number to use, because you can follow it through the drivetrain and it doesn't change (except for loss).

Unlike torque. I notice you have 1000 ft.lbs rear-wheel torque in your sig line for your Cummins. You know it's gotta be way higher than that, right? I'm sure it's 1,000 ft. lbs. at the engine, but it's gotta be around four times higher than that at the rear wheel.

 

You know, you can drive a stickshift truck, park it on a hill, put it in reverse, shut off the motor, and get out and walk away. Now you have a significant amount of torque on the crankshaft, with zero work being done. That's about how useful a torque number alone is.

Yes, if in both cases you also know RPM.

 

I know what your saying I want to know how you to that or why its that way.
Tq is a work force of twisting motion in the engines we're talking about. In order for a shaft to turn there has to be tq. The shaft doesn't have to turn in order for there to be tq. So if the shaft is turning there is always tq. Always.
When you downshift yes you did send more tq and more hp to the rear weither or not the engine built anymore or not. Torqueshift tranny is 1:1 in 4th gear I believe and .73 in 5th. So your cruiseing at 2000 rpm then downshift to 4th even if your only making 5 ftlbs of tq at the engine 5x.73=3.65 ftlbs to the rearend and now 5x1=5 ftlbs to the rearend. What just happend the downshift raised your tq but you have to have a higher rpm to keep the same speed. You have to. So either the higher rpm with no more fuel will slow you down or you add fuel to keep the rpms.
Oh I agree more fuel more rpms more land speed. What I want to know is how does an engine make more or less power at the same rpms. Sounds cut and dry to me. At x rpms this engine's output is y. How much fuel you put to it gets it there or not depending on the load that its under.

 

Dang it, I almost spit out my drink when I read that. I don't care what anyone says...THAT is funny.

 

A semi slows down on hills cause his top gear is so short. Its putting less than the engine to the rear. Any weight going up hill wants to slow down. Semis take out slow cause they have such tall gears. The gear speed ratio is just that low. Buttt the tq that being put back there.
Hp is after all hp. Hp doesn't move trailers. Tq does.

 

The variable in this case is torque. If RPM is constant, higher torque on the crankshaft will result in higher HP.

No, only if there is a load on it.

You have to add the word "maximum". "At x rpms, this engine's MAXIMUM output is y". Translation: It is making the most torque it can without slowing down.

You could have an unloaded engine turning 5,000 rpm, but driving no load. It is producing near zero torque, and thus near zero HP. Start putting a load on it (and adding fuel at the same time, so it maintains at the same rpm). Now you are adding torque, and as you do you are increasing the HP. As you keep adding load, you will reach a point where the engine will begin to slow down, in spite of adding fuel. That is the maximum power for that rpm, and there will be a torque value that will correspond to it.

 

Are we talking about lawn mowers yet?

 

Hold my truck in "N" on a hill and then tell me no works be done.
It doesn't matter if the bolt turns you applied force.
Ok you take your hp that's your right
Do worry about tq.
A 5.4l 4v was had something like 380 hp compair it with a 6.8l that has 365. Aight so you want the 5.4 it sounds the best even though its only makes 360 ftlbs of tq. I'll take the 6.8l.

 

But work is equal to force times distance. If there was no movement there was no work done. Wow, I haven't studied that kind of stuff since I was in high school or collage 30 some years ago.

 

How do you hold a truck in neutral on a hill?

Stick a 2 foot breaker bar on the bolt, hang a 50 lb weight on the end, and walk away. You have 100 ft. lbs. all day long, with zero work being done.


Of course I "worry" about torque, I said that early on. I'd rather tow with my diesel. But torque without HP is worthless.