The equation I showed above came from the science and engineering world but still might be wrong. Note that it says nothing (nor does it need too) about efficiency - it just shows the relationship between crankshaft torque and horsepower output.
Please research a bit and post for us the proper equation for a diesel engine ... but please make sure that the equation includes somewhere in it a value for "torque" and a value for "horsepower" so that - using the math rules for changing around equation structure - that "torque" winds up on the left side of the equal sign and that everything else winds up on the right side of the equal sign.
I'm always open to learning about the proper diesel equation showing the relationship between diesel crankshaft torque and diesel horsepower output.
Thanks in advance.
By the way, maybe this article can help make things pretty clear:
http://lainefamily.com/hp.htm