 The fuselage of the J-4 was wider than the J-3 and the aircraft had a fully enclosed rear decking to the fuselage top.The first J-4s had a Continental 50 hp A50 engine with upward-facing exhaust ports, an open cowl, oil and spring landing gear, a modified tail wheel system and many other changes.The early J-4 had a comfortable cockpit but was slower than most side by side aircraft of the day.