when you get your car scanned, the scanner/computer checks your car engine/sensors/electricals for optimum performance/factory settings.
for a specialized engine performance test, you need to get in touch with some other professional who has the necessary equipment. that test can only be carried out on our motorway or ring road probably where you can floor your car with the diagnostic equipment attached to your car. the readings at that time tell you about the exact performance/under performance of your engine/parts