QC
Supreme Mariner
- Joined
- Mar 22, 2005
- Messages
- 22,783
Re: Factory Horsepower ratings
Hallelujah Bro!!!! This is the most intelligent post in this flipped up thread. OMG!!! Finally some sanity!!!
Those of you who dispute this need to reread and reread and reread, especially the part about multiplying torque yet horsepower stays the same.
MM,
We should jointly write a FAQ on this topic.
Here are some excerpts from a previous post of mine:
. . .on a vehicle where you have solid contact between the crankshaft and the road surface (a tire) you need high low RPM torque values to start that rolling . . . Gearing actually multiplies torque . . . let's say that the torque at 1000 RPM is 100 lb/ft. (using round numbers) The trans reduction is 5, so the resulting torque to the rear end is 500 lb/ft at 200 RPM (I am blowing off efficiency losses through the gear train . . . ) then the rear end reduction is 3 so the 500 lb/ft becomes 1500 lb/ft at 66.6 RPM. That 1500 lb/ft at the axle is divided into two wheels (2WD) and splits this to two 750 lb/ft torque values at the individual wheels . . . Yes the torque causes the vehicle to start rolling . . .
Now to a marine example: I would submit that you could apply a lot of torque to the wheel and tire example above with your hands, and back, and legs, and all youve got, and maybe get a vehicle (light one) to move with your bare hands. Have you ever spun your propeller by hand in the water? Comparably easy huh? This is because the propeller is pretty small and the media that it operates in (water) is not as viscous as the tire and asphalt combo (same reason it doesn't hurt as much to fall in water as it does to fall on asphalt
) . . . Remember the formula? hp = torque x RPM/5252. It is everything, stare at it. This is why boats can live with only one gear; there is no need to multiply torque as there is already more torque available to get the propeller spinning up to max RPM than required.
Mischief said:
Hallelujah Bro!!!! This is the most intelligent post in this flipped up thread. OMG!!! Finally some sanity!!!
Those of you who dispute this need to reread and reread and reread, especially the part about multiplying torque yet horsepower stays the same.
MM,
We should jointly write a FAQ on this topic.
Here are some excerpts from a previous post of mine:
. . .on a vehicle where you have solid contact between the crankshaft and the road surface (a tire) you need high low RPM torque values to start that rolling . . . Gearing actually multiplies torque . . . let's say that the torque at 1000 RPM is 100 lb/ft. (using round numbers) The trans reduction is 5, so the resulting torque to the rear end is 500 lb/ft at 200 RPM (I am blowing off efficiency losses through the gear train . . . ) then the rear end reduction is 3 so the 500 lb/ft becomes 1500 lb/ft at 66.6 RPM. That 1500 lb/ft at the axle is divided into two wheels (2WD) and splits this to two 750 lb/ft torque values at the individual wheels . . . Yes the torque causes the vehicle to start rolling . . .
Now to a marine example: I would submit that you could apply a lot of torque to the wheel and tire example above with your hands, and back, and legs, and all youve got, and maybe get a vehicle (light one) to move with your bare hands. Have you ever spun your propeller by hand in the water? Comparably easy huh? This is because the propeller is pretty small and the media that it operates in (water) is not as viscous as the tire and asphalt combo (same reason it doesn't hurt as much to fall in water as it does to fall on asphalt
) . . . Remember the formula? hp = torque x RPM/5252. It is everything, stare at it. This is why boats can live with only one gear; there is no need to multiply torque as there is already more torque available to get the propeller spinning up to max RPM than required.
