The new Pro Stock rules were simple: carburetors only, gasoline was the fuel, 7 pounds per cubic inch displacement (CID). A typical first-gen Camaro, the early class favorite, with a .030-inch overbored 427 big-block (430 CID) would have a 3,010-pound weight minimum. Former S/S race cars, primarily the popular pony cars, were easily converted to run in Pro Stock. Across the board, engine builders chose a pair of Holley carburetors for their tunnel-ram intake manifolds.
Chevy racers initially selected the Holley R-4224, a 660-cfm “center squirter” four-barrel setup with a deep plenum beneath the carbs. Chrysler teams with 426 Hemis and Ford teams with 427 FE and SOHC 427 engines opted for Holley 4500 carburetors on shallow plenum intakes. When American Motors (AMC) joined the battle, Booth-Arons Racing Enterprises and Maskin & Kanners ran Holleys on their AMC engines.
Headline drivers that jumped into Pro Stock included Don Nicholson, Eddie Schartman; Dave Strickler, Butch Leal, Ronnie Sox, Dick Landy, Arlen Vanke, Bob Lambeck, Ed Miller, Dave Lyall, Gapp & Roush, Roy Hill, Al Joniec, Bill Jenkins, Hubert Platt, Bo Laws, Billy Stepp, Warren Johnson, Mike Fons, Bill Hielscher, Dick Harrell, and others. Those generous car numbers provided plenty of opportunities for match racing and full fields at major events.
Soon after the debut of Pro Stock, Holley identified a problem facing the new Pro Stock racers: the need for increased fuel volume and pressure. Holley answered with the groundbreaking GPH-110, a high-output, rotor-vane, electric fuel pump with an adjustable, external pressure regulator. With a fuel-volume capacity of 110 gallons per hour, the GPH-110 pump was an instant hit and has remained popular for five decades!
Pro Stock technology also had a major impact on Sportsman racing. The trickle-down effect brought Pro Stock technology and Holley products to Modified and Comp Eliminator racing, too.
Although racing in the 1970s took a backseat to the issues of exhaust emissions, fuel economy and vehicle safety, there was still interest from Detroit. Chrysler’s Dodge and Plymouth teams had above-board factory support. The Ford faithful found back-door support from former members of Ford’s once astute race programs. Bill “Grumpy” Jenkins was a frequent visitor at the GM Technical Center in Warren, Michigan. His Malvern, Pennsylvania, shop received a generous supply of key factory components to feed his program. As usual, Holley was the first choice for carburetors and fuel systems. AMC had joined the party in 1968 fielding Holley-equipped, factory-supported race cars in Super Stock, then followed suit in Pro Stock in the 1970s.