Fudging dyno numbers was rampant before all companies switched to SAE Net performance testing proceedures in the early 70s. Before that advertised horsepower and torque numbers were SAE "B" curve numbers which meant no air cleaners (velocity stack "OK"), minimum exhaust backpressure (dyno headers "OK"), unconstrained coolant, air and oil temps, LBT fuel curve, MBT spark curve, no front end accessory drive (idlers only), etc. Maybe even SAE A numbers with a remotely driven water pump snuck in there.
Today SAE C performance numbers are published with the engine run "as installed in a vehicle" with exhaust backpressure restriction and accessories in place, and numbers generated by the average of several runs, not a flyer.
Even so there are ways to make some dyno tests "more equal" than others and for this reason I am always skeptical of dynamometer claims until I see the vehicle performance numbers to back it up, be it an e.t. slip, a land speed record, or lap times.
You should be too.
