of its engine such as idling it runs at high efficiency load conditions only with no 34 part throttle 34 running and provides as an option the recovery and re use of a portion of the vehicle 39 s braking energy it can operate in this manner over wide ranges of atmospheric conditions with mechanisms markedly low in weight size and cost to accomplish this the unthrottled engine pumps hydraulic fluid into a storage chamber at substantially maximum load and drives its vehicle by feeding to its drive motor just enough fluid to meet its immediate power needs it 39 s shut off valves 15 and 16 stop all fluid flow to the drive motor when no power is needed this eliminates a substantial leakage loss optionally the drive motor is used to pump fluid back into the high pressure storage chamber during braking for re use as needed it achieves the necessary degree of power piston stroke uniformity by raising or lowering the pressure in the fluid storage chambers to meet ambient atmospheric conditions and fuel variations such as high or low octane and alcohol blends this is achieved by programming the computer to analyze data from barometric pressure sensor 61 air temperature sensor 62 and humidity sensor 63 accumulator pressure sensors 64 and 65 and.