ATK Engines HP89C GM High Performance 350 Long Block Crate Engine

An ATK Engines HP89C long block, a new 350 cubic inch GM small block rated at 390 horsepower and 420 ft-lbs of torque, built around a 4-bolt main, 1-piece-seal roller block rather than sold as a fully dressed engine.

What's under the hood

Bore and stroke run 4.040 x 3.480 inches, with hypereutectic pistons at 10.1:1 compression, moly rings, and a hydraulic roller camshaft specced at 220/224 degrees of duration on a 110 LSA, run through a double roller timing chain. ATK's aluminum cylinder heads carry 2.020-inch intake and 1.600-inch exhaust valves, topped with billet aluminum 1.6-ratio roller rockers.

What comes with it

This long block ships with the intake manifold, HEI distributor, carburetor, water pump, oil pan, pump, and pickup already fitted, leaving the buyer to add their own accessory drive and exhaust. The rear-sump pan is one detail worth checking against your chassis: it is not built to clear Chevelles with steering linkage routed behind the crossmember, some Corvettes, or 62-67 Chevy IIs. Recommended fuel is 91 octane or higher, with a stall converter in the 2200-2800 range called for on ATK's build sheet.

Common questions

Is this a long block or a complete engine? It is a long block, built around the rotating assembly and heads rather than a fully dressed engine.

What displacement is this engine? 350 cubic inches, GM's small block Chevy platform.

What compression ratio does it run? 10.1:1.