The Govt. Surplus GenSet engine A084 is a four cylinder, four stroke, 1390cc/84cu.in. aircooled flat four with a 3 in. bore and a 3 in. stroke. It was made by the thousands by Hercules and resembles a Lycoming shrunk in the dryer. It has been converted to experimental aircraft use and faily well optimized, making 45 hp @ 3200 rpm with a 54"/27" prop. It is said to be heat limited in the head. There have been some sucessful "fat fin" VW head fixes using TIG welded additions. I would like to avoid as mouch of this as I can. I would like to stroke this engine to 88mm. This yields a 1600cc engine. The piston speed @ 3200 rpm goes from 9.14 m/s to 10.56 m/s. To maintain the lower conservative speed the operating rpm must drop to 2534 rpm. This will allow for a larger prop disc to absorb some additional power. Questions: 1.) Is the increase in head temperature going to be proportional to the increase in displacement, or does "stroke" heat less, given the lower rpm? 2.) The valves are small. Does the increase in stroke allow for the use of the same valves. 3.) If no to the above, is more lift enough to fix the situation?