Horsepower vs. Torque

[tomstehr]

I am just curious abou this one. Since torque is a measurement of rotational force, why are outboards rated in horsepower at the prop instead of torque output? And of all the specs. I can find about my engine, I haven't seen the actual torque output of it. Maybe I am not looking in the right places for answers though!

 

[Scott Danforth]

Re: Horsepower vs. Torque

Horsepower is the calculation of torque x RPM / 5252. or torque is HP x 5252 / RPM. for advertizing and the general public, people think HP. however without knowing the rating system used, the RPM and other factors - comparing two engines of equal hp may be like comparing apples and oranges, however that is how the engines are sold.

 

[tomstehr]

Re: Horsepower vs. Torque

Thanks! I am guessing this a unique formula to outboads?

 

[dingbat]

Re: Horsepower vs. Torque

Thanks! I am guessing this a unique formula to outboads?

Nope. Text book horsepower calculation

 

[tomstehr]

Re: Horsepower vs. Torque

So then, the advertised HP rating of an outboard is at the WOT range? I would guess since there isnt any mention of what rpm to use in formula?

 

[aerobat]

Re: Horsepower vs. Torque

of course. any combustion engine develops its rated maximum power not at any rpm but only at a specified rpm- thats why you seek for a prop that meets the recommended rpm when engine runs at full throttle.

torque is a direct measurable turning force . power output is the calculated product with what force an engine can turn something how fast.

so a low torque high rev engine will have the same power output like a high torque low rev engine. and both will push your boat with the same speed but with different gear ratios to make the prop spin the same rpm,s .

you could say that in a combustion engine torque alone without compraing the rpms means virtually nothing - it all depends how much turning force with what velocity reaches the propeller- and thats your horsepower rating !

cheers !

 

[QC]

Re: Horsepower vs. Torque

I love aerobat!!!! These threads have a way of bringing out misconceptions instead of facts. What he said ^^^^^

 

[Texasmark]

Re: Horsepower vs. Torque

I love aerobat!!!! These threads have a way of bringing out misconceptions instead of facts. What he said ^^^^^

Come on man, this is your forte'. Jump in...........

 

[QC]

Re: Horsepower vs. Torque

In four sentences aerobat has summed up what I have been blathering on about for 7 years . . . Done

 

[CaptainKickback]

Re: Horsepower vs. Torque

In four sentences aerobat has summed up what I have been blathering on about for 7 years . . . Done

QC, as with GPH, I'm with ya man.

 

[aerobat]

Re: Horsepower vs. Torque

I love aerobat!!!!

QC, i hope you are a nice good build girl

 

[QC]

Re: Horsepower vs. Torque

On the Internet, anybody can be anything you want them to be

 

[jevery]

Re: Horsepower vs. Torque

I am just curious abou this one. Since torque is a measurement of rotational force, why are outboards rated in horsepower at the prop instead of torque output? And of all the specs. I can find about my engine, I haven't seen the actual torque output of it. Maybe I am not looking in the right places for answers though!

The EPA maintains and publishes a database of marine engine applications certified to sell in the US. (Here). The database includes horsepower and torque numbers, though, you'll need to apply conversion factors. Interesting reading.

 

[QC]

Re: Horsepower vs. Torque

One thing to ask yourself when thinking about torque and marine engines: What would you do with that number if you had it? And also, how would you utilize peak torque if your engine is rated at say 5500 RPM and peak torque is at 3500?

If you attempt to answer both of those questions literally, the process will lead you to why manufacturers don't publish the numbers. They aren't worth much

 

[Frank Acampora]

Re: Horsepower vs. Torque

As I answered before: I have two engines of equal horsepower. One is 4 cylinder and one is three cylinder. Both produce 90 horsepower BUT the four cylinder engine has greater torque. Since both develop the same horsepower at WOT, they both drive the same hull at 45 MPH top speed, but the four cylinder, because it has greater torque will produce a higher average horsepower at full throttle, zero-45. So, the four cylinder engine gets there faster.

So, we can separate torque rating to some degree and infer some expectations. However as with others, I agree with aerobat.

And aerobat: I am a tall willowy strawberry blonde. My real name is Frankie--LOL

 

[aerobat]

Re: Horsepower vs. Torque

publishing peak or WOT rpm torgue values in outboards would also wrongly blame manufacturers who develop lightweight high rev engines .

do you guess how many people would stay away from the 150 hp@6500rpm outboard and buy instead the 150hp@4500rpm outboard when torque instead of hp would be published? and how many people would wrongly believe to death that they have the stronger, faster engine ?

but when we continue this discussion QC, i quarantee you that you will very soon have a battle to death with myths like "torque wins races" , "torque gets the job done" "torque pulls weight uphill" etc etc. so dont do it. close it. because for people who really want to understand what torque is and what not all essential is said -and the myths will continue regardless what is said.

of course- a pretty girl who loves me, is always welcome for a "deeper" discussion what power and force from a long stroke piston with perfect compression really means - but not via internet but on a calm night in a lonely bay on a boat

 

[tomstehr]

Re: Horsepower vs. Torque

One thing to ask yourself when thinking about torque and marine engines: What would you do with that number if you had it? And also, how would you utilize peak torque if your engine is rated at say 5500 RPM and peak torque is at 3500?

If you attempt to answer both of those questions literally, the process will lead you to why manufacturers don't publish the numbers. They aren't worth much

So, then, what the peak torque of the engine is and where it occurs in the RPM range should have no effect or factor in prop pitch selection? Ok, cool. Thanks guys!

 

[QC]

Re: Horsepower vs. Torque

but when we continue this discussion QC, i quarantee you that you will very soon have a battle to death with myths like "torque wins races" , "torque gets the job done" "torque pulls weight uphill" etc etc. so dont do it. close it. because for people who really want to understand what torque is and what not all essential is said -and the myths will continue regardless what is said.

That's why I started out quiet . . . The funny thing is those who refer to Horsepower as a marketing term. I believe, and strongly, that marketing is how the public got enamored with torque, so much so that they have determined horsepower is meaningless :facepalm:

So, then, what the peak torque of the engine is and where it occurs in the RPM range should have no effect or factor in prop pitch selection? Ok, cool. Thanks guys!

OMG, I will use those two questions forever. It flippin' worked!! Good on ya mate

 

[aerobat]

Re: Horsepower vs. Torque

As I answered before: I have two engines of equal horsepower. One is 4 cylinder and one is three cylinder. Both produce 90 horsepower BUT the four cylinder engine has greater torque. Since both develop the same horsepower at WOT, they both drive the same hull at 45 MPH top speed, but the four cylinder, because it has greater torque will produce a higher average horsepower at full throttle, zero-45. So, the four cylinder engine gets there faster.

frankie my sweet strawberry , please just believe me that from a physical point of view you are dramatically wrong. but not sure if we should explain it here further.

 

[tomstehr]

Re: Horsepower vs. Torque

frankie my sweet strawberry , please just believe me that from a physical point of view you are dramatically wrong. but not sure if we should explain it here further.

Ok.. too late... you have sparked my curiosity. Please explain!