I was under the impression than sun and maha dynos are basically the same thing?
I'll try and explain it as simply as I can. All a dyno does is measures how fast the car can accelerate a known inertia load.
Inertia is the rotational equivalent of mass so instead of force=mass x acceleration, we have torque=inertia x angular acceleration.
Now the dyno does the rotational equivalent of f=ma for the roller and by knowing engine speed can convert that to a torque equivalent at the engines rotational speed.
Now what the dyno doesn't know is the inertia of the rotating bits of the drive train. On coast down, the dyno brakes the roller, and it knows how it should decelerate on its own (known inertia), it can calculate the inertia of the drive train by comparing the deceleration of the roller compared to how it would decelerate on its own.
Now this figure is in no way shape or form a drive train loss. It is the extra inertia that needs to be added to the rollers inertia to get a power figure at the roller.
In other words you get torque =(roller inertia+drivetrain inertia) x angular acceleration.
or as dynos wrongly put it torque=(wheel torque + losses) x angular acceleration.
Now depending on what the roller inertia:drivetrain inertia is, the larger or smaller a dynos drivetrain losses will be.
If the ratio was 3:1, the dyno would claim 25% losses.
If it was 4:1, the dyno would claim 20% losses
If it was 9:1, the dyno would claim 10% losses.
If you take a car and take the wheels off, and attach it to a dynapack you will see higher whp figures, as the wheels are a large part of the drive train inertia, plus it removes the inefficient tyre to roller interface. Think about the wheel. a bit like a flywheel?, a bit like the roller? Is it starting to make any sense yet.
There is no way that by brakeing a drivetrain you can in any way measure it's mechanical losses that would be there when power is applied. To do this you need to have known power going in one end of the drivetrain, measure power coming out the other end, and then take one from the other to get the loss.
The dyno would need to be able to hook up to the input shaft of the gearbox to do this.
Any gearbox or transmission designer that loses more than 5% of input power through noise and heat would be sacked and told to go do something he was good at. The tyres lose a little as well, as they're flexible, and make a little noise and heat, but its a few hp at most.
Let me say it again. A DYNO CANNOT MEASURE THESE LOSSES!
They are measuring the drivetrain inertia to add it to the roller inertia that's all.