Quote:
Originally Posted by DSLeach
If you are able to reduce the rotational mass of the engine and drive train, you will get a higher HP reading on the chassis dyno. Less power used to accelerate rotating mass means more is available to spin the dyno drum.
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One more comment on this one: On the chassis dyno, the car is not accelerating, and when performing the wheel torque measurements, the system is supposed to be
at steady state.
So again NOTHING is accelerating, not the car, not the rotating assembly of the engine, not the drivetrain.
No acceleration - then the mass does not matter - it is a
STATICS problem.
NOW - IF you take a stock car and perform a 1/4 mi run, then using the time it took and the mass of the car, you can calculate the HP.
Next - reduce the rotational mass of the rotating assembly and perform the same test again - WOW faster!
If you do NOT account for the reduced mass of the vehicle as a whole, and do you calculations again, the result will be - MORE HP.
BUT - if you recalculate using the new mass of the car (disregarding the change in rotational inertia of the rotating assembly) your answer will show the same HP to within about 1%.
This is because you can reduce the rotational mass of the flywheel and the pulley, and the driveshaft, and the wheels.
But when compared to the mass of the ENTIRE rotating mass: Pulley(s), belt, alternator, water pump, AC pump, timing chain, cams, crankshaft, pistons, wrist pins, rings, rods, flywheel, pressure plate, clutch disk, transmission input shaft, lay-shaft, gears, driveshaft, DS-bearings, differential, CV joints, axles, wheel bearings, disk brake rotors,
wheels, lugs nuts,
tires - You cannot reduce the MOI of that entire mass by more than about 1%.
