Engine dyno vs chassis dyno

Dynos are a tool nothing more...i had my duster on a chassie dyno 3 years ago some changes were made and the numbers deffinately showed improvement..took it to the track the car ran SLOWER put all the adjustments back to where i had them before the dyno..and the car was running the proper numbers again..what a waste of $200.00..nothing beats real world test and tuning...Mike save your money..