ATK Engines HP55 Small Block Chevy 383 Stroker Base Engine, 500HP

ATK's HP55 is a 383 Small Block Chevy short block rated at 500 HP and 505 TQ, with a lopey idle that, per ATK, can conflict with power brakes or a factory AC compressor. As a short block, it ships with the bottom end and camshaft only; cylinder heads, intake, carburetor, ignition, and accessories are not part of the package.

What's in the short block

Bore/Stroke run 4.040 x 3.750, built around a Scat 4340 forged crankshaft on an external/internal balance split, Scat 4340 forged H beam rods with ARP 8740 bolts, and forged 10.2:1 pistons with moly rings. The hydraulic roller cam specs out at 237/245 degrees of duration on a 112LSA, running through a double roller timing chain.

What you'll need to add

ATK rates this engine's power using Dart SHP aluminum heads with 72cc/200cc runners and 2.02/1.60 valves on billet aluminum 1.6 roller rockers, so plan on sourcing heads to that spec if you want to match the rating. A rear sump 5qt oil pan is the recommended style, but it will not clear some Chevelles with steering behind the crossmember, certain Corvettes, or early Chevy II applications, so check pan clearance for your chassis. ATK also suggests a 2800+ stall converter and 1 ¾" headers for this build.

Common questions

Does this engine include cylinder heads? No, this is a short block; heads are not included.

Can I pair this with power brakes or factory AC? ATK flags that the lopey idle on this build can be a poor match for either one.