Horsepower vs. torque

[ken4831]

It makes it a bit decieving, but no matter how they play with the graphs and scales, the one and only time HP is the same as Torque is at 5252rpm. ANYTIME under that RPM, torque is greater. ANYTIME over it, HP is greater.

Guess when you quote some one at least do the quote line.
Refering to post #22
ken 4831:ashamed:

 

[LD1]

So does that mean two engines, gas and diesel, same horsepower rating, same rpm, the diesel has more torque (which feels like a few more hp) because at that rpm the gasser hasn't reached it's peak torque range that it's rated at?

Not sure what you are asking.

IF the gas and diesel motors have the same HP rating, lets say 300HP.

BUT the gas motor gets that 300HP @ 4500RPM and the diesel makes it @ 2500RPM.....And you are running bothe motors at a constant 2000RPM, the diesel is going to have more HP and Torque at THAT RPM.

But if they are both rated at 300HP at the SAME RPM, they will have the same torque at THAT rpm.

 

[LD1]

Guess when you quote some one at least do the quote line.
Refering to post #22
ken 4831:ashamed:

I dont know why you quoted me and mentioned something about post #22, But you are making absolutly NO sense to me what-so-ever.:confused2:

 

[looknlearn]

Not sure what you are asking.

IF the gas and diesel motors have the same HP rating, lets say 300HP.

BUT the gas motor gets that 300HP @ 4500RPM and the diesel makes it @ 2500RPM.....And you are running bothe motors at a constant 2000RPM, the diesel is going to have more HP and Torque at THAT RPM.

But if they are both rated at 300HP at the SAME RPM, they will have the same torque at THAT rpm.

I was trying to say that when you use each motor at a typical rpm, the diesel will feel like it has more power cause it's torque range is at a reasonable rpm unlike to gasser which's max torque is at an ungodly rpm which it would only last a few minutes at. Is my thought correct?

Just trying to get my head around why a diesel and gas motor with the same hp rating, but the diesel will pull a lot more.

 

[dodge man]

If a diesel and gas motor have the same HP ratings, the odds are the diesel will have more torque. The diesel will also have the max HP and torque at a lower RPM than the gas engine.

I have a 2010 Challenger that I have done a few things to increase the horsepower. Its probably making about 400hp and 400 ft-lbs at the back of the motor, at probably around 5000 rpms. Thats with a 5.7 litre v8 gas engine. If you found a diesel engine in a over the road truck with the same horsepower, it would probably be something like 8 litres, and make something north of 1000 ft-lbs of torque, all below 3500 rpms. In theory, the gas motor in my Challenger has as much HP as that big rig. If you stuck that 5.7 gasser in a big rig, it wouldn't have enough torque to pull up into its power band of 5000 rpms and would be useless, even though it makes as much HP as the big diesel engine.

 

[LD1]

I was trying to say that when you use each motor at a typical rpm, the diesel will feel like it has more power cause it's torque range is at a reasonable rpm unlike to gasser which's max torque is at an ungodly rpm which it would only last a few minutes at. Is my thought correct?

Just trying to get my head around why a diesel and gas motor with the same hp rating, but the diesel will pull a lot more.

That is pretty much it.

If a gas motor and a diesel motor both have the SAME HP rating, the gas motor has to turn a much higher RPM to reach that HP. Therefore the diesel will more than likely have more HP below that RPM.

The thing that has to remain constant is the RPM's. And since HP is a mathematical calculation using ONLY torque and RPM,
IF:
The deisel makes more torque @ 1500RPM vs the gas, it also must make more HP.

If the diesel makes more torque @ 2000RPM vs the gas, it again makes more HP.

So on and so on.

For the gas motors to even get to the same HP rating as a diesel, it needs to turn RPM's in excess of what a diesel can.

Basically Torque and HP are proportional. Two things increase HP. That is torque AND RPM's. So if a diesel and gasser have same HP ratings, the diesel uses gobs of torque and not many RPM's to achieve it. The gasser will use gobs of RPM's but not as much torque to get to the same end result.

The net effect is that the diesel has a power band MUCH lower in the RPM range. That is why they feel like they have more power. And that is why a gas motor will feel more sluggish in comparison because they have to wind up to a much higher RPM to get to the same HP level.

Make sense? Or have I confused you even more:laughing:

 

[slowzuki]

Its a hard concept for people to swallow and the complication that engines only operate at that pretty little curve when at wide open throttle/max fueling also confuses them.

A diesel engine at part load at a good economy rpm, making enough hp to move a vehicle, generally has more torque reserve or room to generate more torque/hp when you mash the pedal without changing rpms.

A gas engine needs to increase its rpm from ideal economy rpm to match the diesels hp so the transmission will need to downshift to allow the engine to generate the power needed. People perceive downshifting as a lack of power and always complain about engines that need to rev out to generate power. For a gas engine thats the way of life.

 

[looknlearn]

Ok, I think I got it,:thumbsup: Thanks for taking the time to explain.

 

[LD1]

Ok, I think I got it,:thumbsup: Thanks for taking the time to explain.

No problem.

 

[Dargo]

Ok, I have a related question. How can someone tell me what they consider a "reasonably accurate" estimation on HP and torque given my 1/4 mile time slip knowing my weight at the line was right at 8200 pounds? Pictured is the time slip. Is it possible for a person to calculate HP and torque assuming that I had minimal tire spin?