A car magazine article states that the power W delivered by

A car magazine article states that the power W ? delivered
by an automobile engine, in hp, is calculated by multiplying
the torque t, in ft ? lbf, by the rotational speed of the
driveshaft v, in RPM, and dividing by a constant:
W = torque *  rotational speed of the driveshaft over C

What is the value and units of the constant C?

Solution

Normally, we write, rotational speed, in Rad/s = 2**RPM / 60
Since you are after the units of the C constant we should do it more proper,
in Rad/s = 2**RPM * [1min/60s]. The squre braket is called a \"unity bracket\" that contain equivalent units for conversion on top and bottom. 1min = 60s, and hence the name \"unity bracket\" !!
= C * RPM , where C = 2**[1min/60s] = /30 min/s
You can go on writting :
HP = T * = T * C * RPM, (C = /30 min/s)

or 2nd method:

W=1 hp=550 (ft*lbf/sec) * 60 (sec/min) = 33,000 (ft*lbf/min)
T= 1 ft*lbf
w= 2*pi (rad/min)

Solving the original equation for C get:

C=T*w/W,

thank you