Is the Mustang dyno in question a 2 roller (1 per axle) or a 4 roller (2 per axle)? It makes a difference.

First off, Dynapack and Dynojet do not use the same math - that statement alone is enough to destroy the credibility of the whole post. The physics of the two machines make it totally impossible to use the same math. They work on totally different principles and different math is required.

Dynojet - is not a device that measures torque. It measures acceleration of a known mass. So they measure acceleration over a period of time, and then calculate the average power required to accelerate the mass at that rate. That power level (plus a known fudge factor they add in) x 5252 / Avg engine RPM in the sample period = torque. So torque is a calculated number derived from an acceleration rate, a "flywheel fudge factor", and an average RPM - kinda fuzzy, but it works OK for what it was designed to do. Also, remember that the power is the acceleration of the roller - not necessarily the same as the power made by the drive axle.

Dynapack measures torque and RPM directly on the axle. RPM is sampled in 1 RPM increments, and actual measured torque for that 1 RPM is multiplied by the axle RPM number / 5252 = actual power on the axle. Pretty direct and simple. Engine RPM is calculated as axle RPM x gear ratio. Flywheel torque is calculated as axle torque / gear ratio x correction factor (if any - most use 1.0 or no correction). This is as close as it gets to direct measurement on a chassis dyno.

So why does a Mustang dyno read lower than a Dynapack? Because it has tires and rollers, and these things have drag and power loss. If it has 4 rollers and 4 wheels, it has a lot of it.

Things you can do to reduce power numbers on a roller dyno:

4 rollers = more drag
small rollers = more drag
wide tires = more drag
sticky tires = more drag
lower tire pressure = more drag
more vehicle weight = more drag
more strap tension = more drag
more camber (from zero) = more drag
More toe in/out = more drag (x2 for AWD)
Heavier wheels and tires = more accel loss
Wheelspin = power loss on the dyno

All of these things will cost you power. On a AWD car, MANY of these things are present. If he has a 4 roller Mustang, the car has wide, sticky tires, with a good amount of toe in the front and rear, lots of camber, tight straps and large/heavy wheels and tires (sounds like a lot of EVO's I've seen), then is it a wonder that you are getting a reading that is lower than a machine that has NONE of these power losses? We are talking about machines that are reading different things. We read what the axle does directly, Mustang reads what the roller did directly. What the roller did isn't the same thing as the torque on the axle - for all of the reasons above.

It isn't an issue of "which dyno is right" - they are both right - they are measuring different things in a different way. It really only matters when guys are trying to one-up each other on the internet and have to have comparable numbers - no two dyno's that I know of have perfectly comparable numbers for a number of reasons.