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

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

The 1965 Pontiac GTO, a true American icon, is a muscle car that needs no introduction. This beastly machine roared onto the scene with a powerful 389 V8 engine and a throaty exhaust note. The GTO's sleek design, coupled with its performance prowess, made it an instant hit. With options like a close-ratio four-speed manual transmission, a limited-slip differential, and upgraded brakes, the GTO could be tailored to any driver's needs. So, what color would you have chosen for your 1965 GTO? Share