Horsepower vs. torque

[brain55]

Instead of just a simple 2 axis graph, with the x-axis (horizontal) being RPM, and the vertical being HP and torque, they probabally have 2 y-axisis. Probabally one to the left being torque and one on the right being HP. If they are not to the same scale, that is where they make the curves intersect wherever they want. BUT if they are to the same scale, they will cross @ 5252

That is exactly what I was thinking. If you look at the actual HP and torque numbers where they intersect the torque will likely be double the HP at approx. 2600 RPM

brian

 

[LD1]

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.

 

[ken4831]

Is this why a 3 h-p or 5 h-p Briggs engine on lawn mower cuts the grass as well as the new 13 h-p to 20 h-p engines. When looking a piston almost interchangeable and stroke same length the only difference I have noticed is years of service. Almost forever for the older and maybe 2 years on the new.
I don't have accurate figures just ball park type. But have changed out more new lawn mowers because cost of repair and still use the old mower because it runs year after year.
ken

 

[LD1]

Is this why a 3 h-p or 5 h-p Briggs engine on lawn mower cuts the grass as well as the new 13 h-p to 20 h-p engines. When looking a piston almost interchangeable and stroke same length the only difference I have noticed is years of service. Almost forever for the older and maybe 2 years on the new.
I don't have accurate figures just ball park type. But have changed out more new lawn mowers because cost of repair and still use the old mower because it runs year after year.
ken

:confused2::confused2:
:confused2::confused2:

 

[looknlearn]

So would the mathematic equation be different for a diesel engine because of more torque at a lower rpm or am I not understanding?

 

[LD1]

So would the mathematic equation be different for a diesel engine because of more torque at a lower rpm or am I not understanding?

NO. Math is the same regardless.

Diesels having more torque down low also mean they would have more HP down low. Since HP is calculated using the torque. If you have more torque to start with at a given RPM, that results in more HP at THAT rpm as well.

Diesels dont make a lot of HP simply because they cannot turn the RPM''s that a gasser can.

For example, a ~400HP modern gasser like in current trucks is making that peak power in the ~4000-5000RPM range. Whereas a ~300HP modern diesel is only spinning ~3000RPM at max. The HP for that gasser down in the range of the diesels max power would be much lower IF the diesel has more torque @ that particular RPM.

So basically, If the diesel has more torque than a gas motor at EVERY point up to the diesels redline of ~3000RPM, it will have more HP as well. But since a gas motor can spin RPM's almost double a diesel, that is how they achieve a greater "PEAK" HP number.

 

[Scrambler82]

Do not want to get into this discussion but to simplify it and as stated earlier; as I have alway stayed it torque gets you moving HP keeps you moving.
Since with a tractor you are moving slow most of the time TORQUE is what you want to look at.

 

[looknlearn]

NO. Math is the same regardless.

Diesels having more torque down low also mean they would have more HP down low. Since HP is calculated using the torque. If you have more torque to start with at a given RPM, that results in more HP at THAT rpm as well.

Diesels dont make a lot of HP simply because they cannot turn the RPM''s that a gasser can.

For example, a ~400HP modern gasser like in current trucks is making that peak power in the ~4000-5000RPM range. Whereas a ~300HP modern diesel is only spinning ~3000RPM at max. The HP for that gasser down in the range of the diesels max power would be much lower IF the diesel has more torque @ that particular RPM.

So basically, If the diesel has more torque than a gas motor at EVERY point up to the diesels redline of ~3000RPM, it will have more HP as well. But since a gas motor can spin RPM's almost double a diesel, that is how they achieve a greater "PEAK" HP number.

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?

 

[Grand_Pooba]

you got that wrong. HP= torque x RPM divided by 5252

You are right. They will ALWAYS cross @ 5252RPM if the engine can rev that fast. Simply because given the equation above, if RPM is 5252 and the constant is 5252, they cancel out. this leaving torque = HP.

Below 5252RPM, torque is ALWAYS higher then HP. And Above that RPM, HP is ALWAYS higher.

That is why if a vehichle has more torque down low in the RPM range, it will also have more HP down their as well.

HP=torque (in lbs) x RPM divided by 63024

HP=torque (ft lbs) x RPM divided by 5252

Not wrong just different units

 

[Johnbro]

This all seems to make sense--thanks for the education. Here's a graph of the Dodge Diesel HP and Torque curves:

At 4000 RPM it makes about 295 lb-ft of torque from this graph. Converting that to HP by the formula above gives us about 225 hp or 165Kw (easier to interpolate on the left side of the graph) which looks about right.

In racing engines, it's a given that torque helps you accelerate and HP increases with RPMs. Until the valves float or the piston goes into orbit, that is