The most notable off-season activity involved Penske Racing and Ilmor. In the summer and fall of 1993, Ilmor and Penske engaged in a new engine project. Under complete secrecy, a purpose-built, V-8 pushrod engine was developed. Mercedes eventually came on board with the project, and badged the engine the Mercedes-Benz 500I. The engine was designed to exploit a perceived loophole that had existed in USAC's rulebook since 1991. While CART sanctioned the rest of the Indycar season, the Indianapolis 500 itself was conducted by USAC under slightly different technical regulations. This effort represented a rare instance during this era where considerable money and effort were invested in creating a powerplant specifically for the Indy 500 by a CART-based team.