Sorry if its been done to death, but id just like peoples opinions on this. As far as i can tell, flywheel hp is almost impossible to calculate accurately. Its my understanding that when a car is put on a dyno, like an inertia dyno. It measures the rate that the wheels can accelerate a certain weight. Then from this, torque is calculated, and then horsepower at the wheels. To then find the flywheel horsepower do they take into account gear ratios of the certain car. Or just use a base value for "loss" like 20%. Surely every car is different?