Chevy 572 vs Ford “Boss 572”: The Rivalry That Never Existed

Two 572-cubic-inch American monsters from Chevrolet and Ford? That sounds like the ultimate big-block showdown. There’s just one problem. Chevrolet really did build and sell the ZZ572 as a factory-backed crate engine. Ford’s legendary NASCAR homologation engine was the Boss 429 — not a factory Boss 572. And that changes this story completely. Chevrolet’s ZZ572 took the traditional big-block Chevy architecture to an extreme 9.4 liters. The street-oriented ZZ572/620 uses: • 572 cubic inches • 4.560-inch bore • 4.375-inch stroke • Gen VI cast-iron big-block • Four-bolt main caps • Forged steel crankshaft • Forged steel connecting rods • Forged aluminum pistons • Aluminum rectangular-port heads • Hydraulic roller camshaft • 9.6:1 compression • Premium pump gas Chevrolet currently rates the ZZ572/620 at 621 horsepower and 645 lb-ft of torque. And for racers, the ZZ572/720R pushes the same displacement to 727 horsepower. Ford’s story was very different. The Boss 429 appeared in 1969 as a NASCAR homologation engine designed to challenge Chrysler’s 426 Hemi. Ford installed it in the Mustang so enough production examples could be sold to satisfy homologation requirements. Kar Kraft in Brighton, Michigan modified the Mustangs to accommodate the enormous engine. But displacement remained 429 cubic inches. Its bore and stroke were 4.360 × 3.590 inches, and Ford officially rated the street version at 375 horsepower. The Boss 429 used Ford’s distinctive semi-hemispherical cylinder-head design and shaft-mounted rocker arms. Despite what is sometimes repeated online, it was not a single-overhead-cam engine. In this video, we explore: • The real Chevrolet ZZ572 • Why 572 cubic inches became possible • ZZ572/620 vs ZZ572/720R • The true history of Ford’s Boss 429 • Why Kar Kraft modified Boss Mustangs • NASCAR homologation rules • Where the “Ford Boss 572” story goes wrong • Factory engines vs modern aftermarket stroker builds • Why the real stories are more interesting than the myth EDITORIAL NOTE: The original narration describes a Ford “572 Boss Hemi” produced in 1968–69 as a limited NASCAR homologation engine. We could not find historical documentation supporting the existence of such a factory Ford engine. Ford’s documented homologation engine was the 429-cubic-inch Boss 429. Ford itself describes the 1969–70 Boss 429 Mustang as the vehicle created to homologate its semi-hemispherical 429 for NASCAR. The narration also gives the alleged Ford 572 a 4.900-inch bore and 3.980-inch stroke. Those dimensions would not produce 572 cubic inches. In Ford engine specifications, 4.900 inches is the bore spacing of the 429/460 engine family — not the Boss 429’s cylinder bore. The actual Boss 429 used a 4.360-inch bore and 3.590-inch stroke. It also did not use single overhead camshafts. The Boss 429 was a pushrod engine with shaft-mounted rocker arms. The Chevrolet timeline needs correction as well. Contemporary coverage describes GM Performance Parts publicly releasing the ZZ572 family in the early 2000s, not developing it as a production crate engine in the early 1990s. Modern builders can create 572-cubic-inch Ford-based stroker engines, including combinations based on Ford’s 385-series architecture. But those should not be confused with a factory-built 1969 “Boss 572” homologation engine. Sources & Further Reading: • Chevrolet Performance — ZZ572/620 and ZZ572/720R • Ford Motor Company — Boss 429 Mustang History • Ford Performance — Engine Specifications • MotorTrend — Boss 429 Mustang History • MotorTrend — GM Performance Parts ZZ572 Which would you rather build: a Chevy ZZ572 or a modern Ford big-block stroker? Subscribe to Epic Motors for more classic-engine battles, engineering history and myths hiding under the hood. #Chevy572 #Boss429 #BigBlock