Eve Optimized Engines provides low expansion ratio variants of six of the game's most popular engines - Swivel, Reliant, Spark, Thud, Skipper and Mainsail. These variants provide greatly improved high ambient pressure performance, which comes by sacrificing low-pressure performance. When operating on Kerbin or in space, stick with the stock engines. But when launching from the surface of Eve, the modified engines provide good first stage power and performance.