David Lloyd's Butler Performance built 421 Tri-power engine on the Dyno. Bored and stroked to 453 cu.in., compression ratio lowered to 9.4:1 for pump gas, B.P. ported & polished cast iron heads, B.P./Comp hyd roller cam. Going in David's 1965 GTO. www.butlerperformance.com #ButlerPerformance #Pontiac | Butler Performance Pontiac

421 SUPER DUTY ON THE DYNO @ Butler Performance!! This 421 SD is using the early "306" heads. These flow a little less than the 1962/ #127's and much less than the 1963/ #980 heads, but it still made great power. Almost 500 HP and well over 500 ft.lbs. of torque!! We actually have both a 1962 389 SD with #127 heads and 1963 421 SD with #980 heads in the shop now that we'll be finishing soon. We love working on these old, rare SD's and really love to hear them scream on the dyno! #ButlerPerforman

1971 Firebird Formula With a 461 Butler Performance Engine Builder: LowCo Joe’s Joe Knepper From SEMA 2017 Video Credit: Internal Combustion/ YT | Butler Performance Pontiac