General diesel question

Can anyone explain to me the difference in HP and torque as it applies at the propeller?? Diesels produce a lot more torque, does that mean a 120hp diesel can turn a bigger prop than a 120hp gas engine. If this is true, would a 120hp diesel be able to push a boat a little faster than a 120hp gas since it can turn more screw at the same RPM???? Inquiring minds want to know. ???

[captbent]

WHATS THE RPMS,HP and torque AT RPM

[Skools Out]

a general rule is a 160 HP Diesel is equal to a 260 HP Gas so figure the math lol

[chitbob1]

a diesel can't turn but half the rpm of a gas engine you have got to make up the difference in gearing that is in a real diesel not a wanna be

[Franco]

1 horsepower is equivalent to 746 watts. So if you took a 1-horsepower horse and put it on a treadmill, it could operate a generator producing a continuous 746 watts.

1 horsepower (over the course of an hour) is equivalent to 2,545 BTU (British thermal units). If you took that 746 watts and ran it through an electric heater for an hour, it would produce 2,545 BTU (where a BTU is the amount of energy needed to raise the temperature of 1 pound of water 1 degree F).

One BTU is equal to 1,055 joules, or 252 gram-calories or 0.252 food Calories. Presumably, a horse producing 1 horsepower would burn 641 Calories in one hour if it were 100-percent efficient.


Torque is a force that tends to rotate or turn things. You generate a torque any time you apply a force using a wrench. Tightening the lug nuts on your wheels is a good example. When you use a wrench, you apply a force to the handle. This force creates a torque on the lug nut, which tends to turn the lug nut.
English units of torque are pound-inches or pound-feet; the SI unit is the Newton-meter. Notice that the torque units contain a distance and a force. To calculate the torque, you just multiply the force by the distance from the center. In the case of the lug nuts, if the wrench is a foot long, and you put 200 pounds of force on it, you are generating 200 pound-feet of torque. If you use a 2-foot wrench, you only need to put 100 pounds of force on it to generate the same torque


There ya go, I'm sure this cleared up any questions you might have. ???

[bigshrimpin]

I'll take a shot at this one. *Correct me if I make a mistake . . . it's still a little cloudy in my head. * Where's CB on this? *

1. *" Can anyone explain to me the difference in HP and torque as it applies at the propeller?? "

Torque (not HP) is the force required to turn the shaft or spin the prop. *

HP is the speed at which you apply the force or perform the rountine( I think ???)

HP is higher on gas motors b/c they can spin at a faster RPM. *

Engines with equal HP . . . does not mean they can generate the same twisting force (torque). *That's why you have big *** trucks that tow huges loads with only 290hp diesels.

HP = Torque * RPM / 5,252 *

Motors generate MAX HP at MAX RPM.
So if you compare the follow two motors

120hp diesel with a max RPM of 2800
120hp gasoline motor with a max RPM of 5000

120hp = (x foot pounds ** 5000RPM)/ 5252
120hp = (x foot pounds ** 2800RPM)/ 5252

120hp Gas Motor @ 5000rpm * * *=126 ft of torque.
120hp Diesel Motor @ 2800rpm *= 225 ft of torque.


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2. * Diesels produce a lot more torque, does that mean a 120hp diesel can turn a bigger prop than a 120hp gas engine? *

"maybe" * 225 foot pounds of torque is more than 126 foot Pounds . . . . so the engine should be able to turn a much bigger prop . . . except that people had to screw the simple math up with a gear box.
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3. *"If this is true, would a 120hp diesel be able to push a boat a little faster than a 120hp gas since it can turn more screw at the same RPM?" *

It gets tricky . . . Weight is a big factor in determining the speed of a boat. *Also a gear box with a lower gear ratio allows the powertrain??? to generate more torque. *
*
500hp @ 1:1 @ 2000rpm = 1313 pound feet of torque

485hp @ 3:1 @ 667rpm * = 3819 pound feet of torque
(500 - friction of gears) *

Then you get into some thrust equasion and prop efficency and that's about where I gave up. *:-/

[reelapeelin]

Torques my joules juss thinkin' about it... ::)...

[Blue_Runner]

...now THAT is why I failed physics in High School :P

Originally Posted by bigshrimpin

HP is the speed at which you apply the force or perform the rountine( I think ???)
Engines with equal HP . . . does not mean they can generate the same twisting force (torque). *That's why you have big *** trucks that tow huges loads with only 290hp diesels..
So*:-/

This is the part of the whole deal that leads me to believe that a/my V20 would get more speed out of a 120hp 195ft lb of torque diesel than 120 hp mercruiser..with the appropriate prop of course. I have no idea what the toque is on the merc. the diesel produces max torque at 2300 rpm and max hp 4400rpm

[bigshrimpin]

http://www.cmdmarine.com/PDFs/4081824_1104.pdf

That setup would be perfect for the v20.