09/04/2026
We covered the ZZ632 on this page. 1,004 HP from 632 cubic inches. The most powerful naturally aspirated crate engine ever sold. The ZZ572/720R is its older sibling and its philosophical ancestor: the same big block Chevy family, the same Chevrolet Performance catalog, the same cast iron block with four bolt mains, the same forged everything. But where the ZZ632 represents the absolute ceiling of naturally aspirated displacement, the ZZ572 represents something different. It is the Rat Motor at maximum tune on race fuel. The King of the Rats. And it has been pulling bracket racers into the nine second zone for years while the ZZ632 gets the magazine covers.
The specifications are brutal. Bore 4.560 inches. Stroke 4.375 inches. 572 cubic inches from a tall deck Gen VI big block Chevy casting. Forged 4340 steel crankshaft. Forged 4340 H-beam connecting rods, shot peened. Forged aluminum pistons with full floating wrist pins. Four bolt main caps. 12.0 to 1 compression ratio. That compression number is the detail that separates the ZZ572 from street engines: at 12 to 1, the engine requires 110 octane race fuel. Not 93. Not E85. One hundred ten octane leaded racing gasoline. This engine cannot run on pump gas without detonation destroying the pistons within minutes. The ZZ572/720R is not a street engine disguised as a race engine. It is a race engine sold in a crate with a part number and a factory warranty.
The cylinder heads are where the power lives. Aluminum rectangular port castings with 310cc intake passages. Three hundred ten cubic centimeters of intake port volume is enormous. For comparison, a factory LS3 head has 260cc intake ports. The ZZ632's RS-X spread port heads have even larger ports. The ZZ572's 310cc ports are sized for an engine that makes its power between 4,500 and 6,750 RPM with a mechanical roller camshaft running .714 inches of lift on both intake and exhaust. Duration: 278 degrees intake, 282 degrees exhaust at .050 inch. Those are race cam numbers. The mechanical roller lifters require periodic valve lash adjustment, something hydraulic lifter engines don't need, but they allow the aggressive ramp rates and high lift that the big ports demand. Valve sizes: 2.250 inch intake, 1.880 inch exhaust, stainless steel. A 1,150 CFM Holley Dominator carburetor sits on top. One thousand one hundred fifty CFM. The largest production carburetor Holley makes, feeding 572 cubic inches that consume air at a rate that would starve a smaller carb at 6,000 RPM.
Output: 727 HP at 6,300 RPM and 680 lb-ft at 4,900 RPM. Those numbers are conservative by modern aftermarket standards. The NRE 540 makes 1,100 HP from fewer cubic inches with turbos. Kenny Duttweiler's Bonneville engines make 3,000 HP from 557 cubic inches with twin turbos on methanol. But the ZZ572 makes its 727 HP naturally aspirated, on a single carburetor, with factory components, from a crate engine you can order from a Chevrolet dealer with a credit card and have delivered to your garage on a pallet. No turbo fabrication. No custom fuel system. No engine management tuning. Bolt on the included Dominator carburetor, add a starter and fuel pump, and the engine is ready to run. Chevrolet lists it as capable of pulling bracket racers and heads-up cars into the nine second range. Nine seconds in the quarter mile from a crate engine with a factory part number.
Chevrolet also offers the ZZ572/620 at the same 572 cubic inches but with 9.6 to 1 compression, a hydraulic roller cam (.632 inch lift), an 850 CFM carburetor, and 621 HP. The 620 runs on premium pump gas. The 720R runs on race fuel. Same block. Same bore and stroke. Same displacement. Different cam, different compression, different fuel, different power. The difference between 621 and 727 HP is the difference between a street engine and a race engine. Same architecture. Different commitment.
