Abstract: A system for wheeled land vehicles stores energy in a spring when the vehicle is braking, as when stopping or going downhill, and releases energy stored to help the vehicle engine when starting or when going uphill. A mercury switch can serve as an inclinometer in a simple version of the invention. The mercury switch when tipped in downhill direction, actuates a clutch system that, for braking, connects a first end of a coil spring to the engine driveshaft and a second end of the coil spring to the frame of the vehicle, for winding up the coil spring in braking and for steering braking energy in the coil spring. When the mercury switch is tipped in uphill direction, it actuates the clutch system so that it disconnects the first end of the coil spring from the engine driveshaft and connects it to the frame of the vehicle, and disconnects the second end of the coil spring from the frame of the vehicle and connects it to the engine driveshaft, helping power the vehicle.