could be ordered with the ZL-1 aluminum-block 427 adaption of the 1967 L-88 427 Corvette cowl-induction 'ZL-2' hood available for both single and dual four-barrel induction systems that were sealed to the air cleaner base ensuring dense cooler, high-pressure, oxygen-laiden air from the center of the base of the windshield was supplied to the engine for combustion smoothness and maximum power production. Another popular service-parts-only component used on the 302 was the magnetic-pulse Delco transistor-ignition ball bearing distributor. Introduced in 1963 on Pontiac's drag racing engines, General Motors fitted it to the 1967 Z/28 before they used it on the L88 Corvette. It eliminated the production breaker-point ignition allowing greater spark energy and more stable ignition timing at all engine speeds including idle. This was one of the least talked about yet most transformative and comprehensive performance and durability upgrades of its time. Many of the 302s off-road service parts were the development work of racers like Roger Penske. Every part in a SCCA Trans-Am engine had to be available through local Chevrolet parts departments to encourage their use by anyone who wanted them. While the 302 became a strong Limited Sportsman oval track racing engine in the hands of racers like Bud Lunsford in his 1966 Chevy II, its bore/stroke and rod/stroke geometries made it a natural high-rpm road-racing engine and were responsible for its being among the more reliable production street engines homologated for full competition across all the American makes, winning back-to-back Trans-Am Championships at the hands of Mark Donohue in 1968 and 1969. However, with engines built by Al Bartz, Falconer & Dunn and Traco Engineering, the pinnacle of the 302's use in professional racing was its being the primary engine that powered the outstanding but overshadowed 1968-1976 Formula 5000 Championship Series, a SCCA Formula A open-wheel class designed for lower cost. The engine was also popular in Formula 5000 racing around the world, especially in Australia and New Zealand where it proved more powerful than the Repco-Holden V8. Weighing , with a iron block and head engine positioned near the car's polar moment of inertia for responsive turn pivoting, a Hewland 5-spd. magnesium transaxle, and wide front/ wide rear magnesium wheels, it produced incredibly exciting racing. They ran in 2.8 seconds and over . Reminiscing about the series, mid-70s Australian F5000 driver Bruce Allison said, "We never used first gear at the start. We started