The object of this study was to determine the advantages of using the Materiel Division indicator on a cylinder of the supercharged SV-1570 engine. A reliable indicator can be used to good advantage in arriving at the best valve timing to use on a high speed aircraft engine. Optimum valve timing for supercharged aircraft engines differs little, if any, from optimum timing for unsupercharged engines, except possibly at great altitudes, using considerable boost. The period of overlap of exhaust and intake valves has a marked effect on power output and fuel economy, both as to length of overlap period and time in the cycle. Well-designed divided exhaust manifolds, with proper valve timing, actually increase cylinder scavenging, resulting in increased power, by eliminating overlap of exhaust strokes, and by the ejector action of one exhaust "puff" on the previous one.