Torque vs. Horsepower, who gets it?

[HT32BSX115]

Re: Torque vs. Horsepower, who gets it?

Until one understands how Torque, HP, WOT rpm, gear ratio, and prop size all work together, then they just don't understand boats.

Ahhh......yup.

 

[joewithaboat]

Re: Torque vs. Horsepower, who gets it?

Whats to understand, if the o/p puts a healthy small block in place of that pig of a diesel, its going to go faster! Right?
Just sayin....

 

[g1sammons]

Re: Torque vs. Horsepower, who gets it?

Certenly should
But thu all this what iv been trying to explain is hp is a observation of torque and what it can do for a lenth of time
Hp is not a force it's a measure of it
A motor makes torque if we measure it in ft-lbs than the only other factor is time and we can't change time so the only thing we can change is torque
You can't change the hp it's just a unit of measure rather your torque will change it

 

[QC]

Re: Torque vs. Horsepower, who gets it?

Torque is a force and HP is work. Quit trying to pretend that it doesn't matter. That measurement is all that you can use to calc speed. In fact Torque is a direct result of cylinder pressure. If I raise cylinder pressure by 10% how fast am I going to go?

 

[HT32BSX115]

Re: Torque vs. Horsepower, who gets it?

You know I had to go back to Classical Dynamics (which I learned in Physics in the 70's......and mostly forgot in the 80's and 90's!!)

(if anyone wants to read about it, Here's an excellent intro. ) It's a PDF so Acrobat reader, (or whatever PDF reader you're using) will open and display it.

Torque is a force and HP is work

Well, sort-of true.......... Force (F) is applied linearly, TORQUE (F x r) has to be considered with a radius (r) ......so specifically, Torque is rotational equivalent of Force.



But you MUST have the other required component for it to do that work. Speed. (rotational speed......or RPM)

And for example, 400ft-lbs at 2000 RPM is of course, VASTLY different from 400ft-lbs at 3000 RPM


HP is simply the result of a math calculation.

AND HP is a marketing item. .......... to get people to buy a car, boat, engine, etc. The HP is calculated where it gives the most bang for the buck (from a sales point of view)



If you put a sales brochure together that tells the customer that his engine produces 274 lb-ft of torque at cruising RPM (and it won't be all that different than the other model that does the same thing) it won't be a selling point.

But if you tell them that the super wiz-bang engine makes 400 HP! (even though it's at an RPM the customer will NEVER operate at!!!) YOU HAVE A SALE!!!!!

We've been conditioned to be responsive to that!!! ...........The rest of it is just math. Pretty boring math if you read that great intro to Dynamics above, AND you're an engineer type like me!! :facepalm:....

 

[stackz]

Re: Torque vs. Horsepower, who gets it?

two engines side by side. assume all other things are equal except hp and torque.

one makes 250hp and 600ft-lb, the other makes 600hp and 250ft-lb. If I'm going to pick an engine to pull a lot of weight, I'm going with the first one.

diesels in vehicles win out due to the amount of gears they have in the transmissions to keep the engines at their peak torque.

though, with a single speed transmission, and pushing a heavy object through water, I'll take 225hp/385ft-lb peaking @5400rpm versus 200hp/500ft-lb peaking at @3200rpm. sure it'll take a little longer to get up to speed but once its up to speed, the engine will shine more.

his choice to go with a diesel engine was cool and all but there's a reason that boat came with a 360 from the factory.

you guys are staying way to narrow with the discussion by JUST comparing torque to hp without considering rpm enacted to the prop. obviously you have to address issues with cavitation at the prop, drag, etc. but I'd still rather have the prop spinning 5400rpm versus 3200rpm if overall speed is the big issue. the faster is spins efficiently without slipping, etc, the faster you go if you only have one transmission speed to work with.

 

[QC]

Re: Torque vs. Horsepower, who gets it?

Dang Rick, not you too . . . :facepalm:

And for example, 400ft-lbs at 2000 RPM is of course, VASTLY different from 400ft-lbs at 3000 RPM

Of course it is, but, eh . . . the vast difference is horsepower!! God, what is flippin' wrong here? Ahhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh!!!!!!

HP is simply the result of a math calculation.

AND HP is a marketing item. .......... to get people to buy a car, boat, engine, etc.

Hellllllppppppp!!!!! Where's 45Auto? Help!!!! When we sell a 4000 hp compressor drive engine I promise we are not simply BSng for some marketing reason. The customer flippin' needs 4000 hp to drive his flippin' compressors. He could not care less if it has 4000 lb ft torque as long as there is enough horsepower to keep the compressors compressing. Are you guys suggesting that James Watt was all flipped up? He was thinking about brochures? Ahhhhhhhhhhhhhhhhhhhhhhhh!! Rick, Rick, are you telling me you care more about the force twisting the shaft than thrust when you're at 30,000 ft? For God's sake man, I'm dying here, throw me a flippin' parachute . . .

 

[stackz]

Re: Torque vs. Horsepower, who gets it?

are you telling me you care more about the force twisting the shaft than thrust when you're at 30,000 ft?

are you baiting people? thrust and torque are the same type. they are both forces. hp and propulsive power are the results of the work calculation for each.

 

[QC]

Re: Torque vs. Horsepower, who gets it?

Yeah, I get that. Rick is a pilot I think . . . That's all.

I am about to give up. You suggesting that 250 hp is better than 600 hp if you want "to pick an engine to pull a lot of weight" is about all I can handle . . . 600 hp will pull more weight. Yes, it has to be geared right. Maybe there is another way to handle this. What about a Locomotive. The electric motor is the transmission. What's going to make the train go faster and "pull more weight". A generator driven by a 600 hp engine or a 250 hp engine? Don't need to talk hz here please.

 

[Luhrs28]

Re: Torque vs. Horsepower, who gets it?

If you guys keep this up, as punishment I'm not going to post photos and videos of my new engine.

 

[QC]

Re: Torque vs. Horsepower, who gets it?

The only point I am trying to make is that horsepower is a valid measurement, and when calculating things like boat speed you can't do it with torque alone. It is so simple. Half of you post the same, and then contradict it within the post. I will never understand it.

Funny comment from Rick as I have often concluded that those who insist that torque is "all that matters" are victims of marketing campaigns. And the ironic thing is I have sold, serviced and applied high torque rise diesels my entire career . . . I guarantee you I know the benefit of high peak torque values. Any of you ever hand drawn an 18 speed split chart and then calc'ed the gradeability at rated RPM and at peak torque RPM? Once in a while the peak torque road speed is higher one gear higher, but again, how in heck am I going to do that in a marine application? You can't. Quit mixing up wheeled and propeller driven stuff. I made the mistake of trying to compare a jet engine, but that was simply for Rick. Sorry.

Another thing I have always insisted is that torque without RPM doesn't get you much, and if you have both torque and RPM the result is horsepower, so how can horsepower be only important for brochures? Are Mercury, Evinrude, Johnson, Mercruiser, Caterpillar, Cummins all simply scammers? Or do they understand that horsepower is what they literally sell? If they sold torque, don't you think they might brand them with that number instead? The reason they don't is you cannot figure out how much work you just bought. You can't figure out how much fuel you will burn with just torque. You can't tell how fast you will move things, how hard you compress gasses, generate stuff etc.

 

[parrisw]

Re: Torque vs. Horsepower, who gets it?

Are Mercury, Evinrude, Johnson, Mercruiser, Caterpillar, Cummins all simply scammers? Or do they understand that horsepower is what they literally sell? If they sold torque, don't you think they might brand them with that number instead? :

I'm pretty sure I said that a while back, but you were too busy disagreeing with everyone to notice!:facepalm:

 

[QC]

Re: Torque vs. Horsepower, who gets it?

No I saw it, you said "horsepower sells, and torque wins races". Maybe at the drag strip. Not on the water it doesn't. . . .

The way these threads always go. I either shut my mouth and let the inaccuracies (semantics only some of it for sure) continue. Orrrr, I actually try and persevere on what I promise is factual. To say that Horsepower is just marketing is flippin' ludicrous. I will concede one inaccuracy on my part, when I was speaking to Rick, and that is the thrust and torque comparison.

In some simple ways, everyone is correct here. Yes torque is all that matters if you add maintained at any RPM. The only problem with that, again, is that when you add RPM, what you get is horsepower. So either James Watt was a fool, or we're just not communicating.

 

[HT32BSX115]

Re: Torque vs. Horsepower, who gets it?

Another thing I have always insisted is that torque without RPM doesn't get you much, and if you have both torque and RPM the result is horsepower,

That's true. It's a simple calculation ...................HP = (Torque * RPM) / 5252

At zero RPM considering HP is truly meaningless. But I wouldn't say it doesn't "get you much"......


Using the above "formula" a 1940's vintage BIGBOY articulating steam locomotive that weighed over 1,000,000 LBS, (with a 3600TON load behind it) would have ZERO HP when it started moving that entire train.

HP= Torque (times) ZERO divided by 5252 and that equals ZERO Here's a case where RPM was ZERO and the HP was ZERO!

Quit mixing up wheeled and propeller driven stuff. I made the mistake of trying to compare a jet engine, but that was simply for Rick. Sorry.

There's nothing really wrong with "mixing" it up. Torque at a given RPM in a propeller driven aircraft engine will produce thrust. it's directly related.

You can even relate jet engine "thrust" to propeller driven "thrust". It's just that to get the equivalent amount of thrust from a piston engine you need several thousand "HP" to do it with a given propeller @ a given RPM................. AND you have to make the calculation based on a particular propeller RPM.

The only point I am trying to make is that horsepower is a valid measurement, and when calculating things like boat speed you can't do it with torque alone.

I agree. I never said it wasn't "valid" I just said it's used as a selling point because most of the "buyers" understand HP as a relative measurement.

You can't do it with RPM alone either In Fact, you cannot separate RPM and torque because they are directly related mathematically.

My original point for Bert was to illustrate that the engine he chose simply didn't produce enough torque OR HP to do the job.

or we're just not communicating.

Well.....that too!!

 

[QC]

Re: Torque vs. Horsepower, who gets it?

We are in sync

BTW, doesn't the steam locomotive kinda always do a kinda burnout as soon as the steam piston pushes down once? Isn't that then rotational and we have ourselves some ponies? I get your point, but still even at 1 RPM the massive torque just made horsepower . . .

 

[HT32BSX115]

Re: Torque vs. Horsepower, who gets it?

we are in sync

aaaaahhhhhmmmmmmm!!!!!!!

 

[QC]

Re: Torque vs. Horsepower, who gets it?

Oops added a little . . . :redface:

 

[scipper77]

Re: Torque vs. Horsepower, who gets it?

I am still done debating this, I just wanted to comment how funny this thread is becoming to me.

It's tricky to wrap your brain around all of this. Is hp really equal to work or is it power which is a rate of work?

 

[QC]

Re: Torque vs. Horsepower, who gets it?

Torque is work, power is rate of work. kW, horsepower etc. "Rate" is where this gets all flipped up . . . dang clock!!!

 

[scipper77]

Re: Torque vs. Horsepower, who gets it?

Read this. It's a pretty good explanation if you can follow it.
http://www.allpar.com/eek/hp-vs-torque.html