Re: Good Question about Horsepower

[John Cunningham <johnc@together.net>]

my understandings differ actually...

Don Muirhead wrote:

> Stephen:
>
> Hate to disagree with another canajun, but you measure HP/torque using a
> dynamometer using various rpm's to measure the load of your engine starting
> with a guesstimate of the red-line of say 7-8,000 and reduce by 500 rpm's

yesssss but the testing is still all done at WOT.  as i understand it, rpm is
held by varying the water brake.  amount of brake required at any given rpm is
how torque is measured.

> thereafter making notes of hp and torque at each level.   What you end up
> with is a hp and torque curve.  In all engines there is a peak in hp/rpm
> followed by a gradual loss - ditto for torque.  Where the hp/torque
> intersect is generally considered your torque rating and he peak hp point
> on your graph your hp.

well, nooo.  hp is derived from torque in the formula:

hp = torque x rpm / 5252
(5252 = 60 sec. in a minute * 2pi * 550)

so below 5252 rpm torque will be higher than its horsepower, above 5252 rpm
every engine's horsepower will be higher than its torque. they will always
cross at that point.  so you really can't make any observations based on
comparing the empirical values of each, i.e. graphing them against each other.

awaiting corrections...

JC