Design Goals:

The goal for the engine modifications is to increase the efficiency of the engine to obtain a fuel efficiency of over 500 miles per gallon. To achieve this goal, the vehicle power requirements must be determined based on the desired operating speed. Due to the nature of the competition, this calls for a decrease in the horsepower of the stock engine from 3.3 hp to 1-1.5 hp. This will allow for less fuel to be burned to achieve our goal output of around 2000 rpm. Thermodynamic efficiencies and compression ratio must also be analyzed.

Design:

In order to decrease the horsepower of the stock engine and increase the compression ratio, the diameter of the bore will be made smaller. To change the bore of the cylinder while keeping the original Briggs & Stratton cylinder, a cylinder sleeve will be placed inside the engine cylinder. The predator 79cc engine will be used as a donor engine for decreasing the bore (6.8 cm to 5.2 cm), which decreases the combustion chamber volume by a factor of 2.7. A new connecting rod will be manufactured that will be able to connect the donor piston to the crank shaft of the Briggs & Stratton Engine. As a result of the new engine head, the distance from the cam shaft to the rocker arms on the engine head is now shorter. New push rods will be fabricated to connect the cams on the cam shaft to the rocker arms on the engine head. Also, because the valve springs on the donor head are lighter from those on the stock Briggs & Stratton, the cams on the cam shaft will have to be grinded to match the profile of the cams on the Predator engine.