Technical specifications for the Indianapolis 500 are currently written by IndyCar. Rules are generally the same as every other IndyCar race. In the past, particularly during the era in which USAC sanctioned the Indy 500 (but CART sanctioned the other Indy car races), rules at Indy slightly differed at times. The result, for example, would be a particular chassis or engine configuration being legal at Indy, but not so at the CART-sanctioned events. This was rather commonplace in the 1980s and early 1990s, when "stock-block" engines (namely the V-6 Buick) were allotted an increased level of turbocharger boost by USAC at Indy, compared to the purpose-built V-8 quad-cam engines. While the "stock block" engines were technically legal in CART competition, they were not given the increased boost advantage, which effectively rendered them uncompetitive, and precluded their use by teams. The most famous manifestation of the USAC rules disparity was the Ilmor-built Mercedes-Benz 500I engine fielded by Roger Penske in 1994.