This Engineering Research Circular published in 1931 investigates the impact of compression ratio, mixture ratio, and spark timing on engine performance using standard motor fuel. A study conducted at the University of Michigan's Automotive Laboratory utilized an N.A.C.A. Universal Test Engine to provide quantitative data on engine power and detonation behavior. Engine Performance at High Compression Ratios shows that while power increases with higher compression ratios—even after detonation begins—it eventually decreases as detonation becomes severe. With detailed graphical analyses, the circular reveals that compression engines, equipped with proper spark control, can efficiently use both ordinary and high-quality anti-knock fuels without compromising power.