HP Ratings

[gtj]

Dear Group,

 

I was wondering if some of you could enlighten me on the various ratings for HP (horsepower) and what the most common recent ratings are likely to depict.

 

I find it confusing at times when some ratings, I believe, are refering to a rear wheel rating and others possibly a rating derived from the crankshaft.

 

Is there a certain percentage of HP loss that one can utilise in aproximating the rear wheel HP if the crank HP is a known value assuming the vehicle is a 1/2 or 3/4 ton PU or SUV?

 

Is torque possibly a more important value to use?

 

Trying to learn a little ....

 

If there is a web site containg more info that you could point me to, that would be great as well.

 

Thanking You In Adavnce,

Glenn

[snoman]

Dear Group,

 

I was wondering if some of you could enlighten me on the various ratings for HP (horsepower) and what the most common recent ratings are likely to depict.

 

I find it confusing at times when some ratings, I believe, are refering to a rear wheel rating and others possibly a rating derived from the crankshaft.

 

Is there a certain percentage of HP loss that one can utilise in aproximating the rear wheel HP if the crank HP is a known value assuming the vehicle is a 1/2 or 3/4 ton PU or SUV?

 

Is torque possibly a more important value to use?

 

Trying to learn a little ....

 

If there is a web site containg more info that you could point me to, that would be great as well.

 

Thanking You In Adavnce,

Glenn

 

<{POST_SNAPBACK}>

 

 

 

 

Generally there is between a 15 to 30% power lose in drive train with front wheel drive being the champ here hands down and rear wheel drive 4x4 being the worst. A simple formula for HP is "torque x RPM / 5252" and with that if you know the torque of a engine at any given RPM you can calulate the HP. Also torque = "(HP / RPM) x 5252"

[PeterbiltChrome]

the engine is the source of the power, and everything that the engine drives is a parasite that saps power from it. Some gets lost in the tranny, inertia of drivelines/wheels, resistance from lubricant....and so on. crank HP is the initial figure and rear wheel HP is power that actually got to the ground to move you along.

 

HP is a measure of work being done by the engine. Torque is the force that the engine has to do the work.

 

Edit: oh, and try www.howstuffworks.com and search for whatever you think of, like horsepower...

[snoman]

HP is a measure of work being done by the engine.  Torque is the force that the engine has to do the work.

 

 

 

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Pretty much except HP is a function of torque "and" RPM so 400 ftlbs or torque at 4000 rpm produces twice as much HP as 400 ftlb at 2000 RPM or the same HP as 800ftlbs at 2000 RPM. BTW, in theory, one horse power will do 33,000 ftlbs of work a minute (ie lift 33,000lbs one foot or 330 lbs 100 feet in one minute)