I use engine dyno testing to see what the changes I do on the motor that day read on the dyno sheets, I have found once I have maxed the motor out on the dyno I may, and I have had to several times, retune the motor in the car at the track to get the best time slip and spark plug readings
The only thing that can't normally be made to LIE is the time slip and spark plugs when you shut the motor off at the finish line after shifting it into neutral
My message is the engine on the dyno is sitting in a control environment room with no oil or gasoline being slosh around like actually happens to the motor in the car
As already brought up you need to test at the track on the starting line RPM and shift RPM to find out what makes YOUR CAR go the fastest that day