The Lotus 56 used a modified version of the ST6 gas turbine used on the STP-Paxton Turbocar ("Silent Sam") that almost won in 1967. The ST6 was based on a small aircraft engine that became one of the most popular turboprop aircraft engines in history. But the car itself was an entirely new and more advanced design which introduced a distinctive aerodynamic wedge-shaped body rather than a cigar-shape, in the year of the introduction of front and rear wings to F1. USAC, the governing body of the Indy 500, had implemented new rules aimed at handicapping turbine powered racing cars by drastically reducing the air intake size. The Lotus 56 made up for reduced power with a sophisticated suspension design, retaining the four-wheel drive concept of the Silent Sam, but with lighter weight, and advanced aerodynamics.