ATK HP33M Chevy 383 Vortec Stroker Mid Dress Engine 390HP

The ATK HP33M pairs a 383 stroker bottom end with Dart Vortec-style cast-iron heads carrying 2.02/1.60 valves, for 390 hp and 460 lb-ft of torque out of a factory-style head casting rather than a big-port aluminum head.

What mid-dress means here

Underneath, Scat's nodular-iron crank turns I-beam rods secured with ARP 8740 bolts, under hypereutectic pistons at 9.5:1 compression. Ignition and the water side ship mounted: the distributor, water pump, and balancer are already in place, with the dual-plane intake bolted to the heads.

What to check before you buy

• Because the timing here is set through the PCM rather than the distributor, your ECM calibration needs to match this cam and head combination.
• The oil pump is a Melling unit at standard volume, nothing upgraded for this combination.
• Fuel delivery is left to you: the carburetor and fuel pump are not mounted, only listed as ATK's suggested parts.

Common questions

Why Vortec-style heads on a stroker? ATK pairs this stroker rotating assembly with cast-iron heads instead of the larger aluminum heads used on its higher-output 383 builds.

Is the ignition hardware in place? Yes, the distributor and water pump are mounted; what's missing is the spark plugs and plug wires, left as ATK's suggested parts.

Why hypereutectic pistons instead of forged? ATK pairs the Vortec-style heads here with 9.5:1-compression hypereutectic pistons rather than the forged pistons used on its aluminum-headed 383s. California requires BAR compliance for engine swap installations.