ATK HP55C Chevy 383 Stroker Complete Engine 500HP

ATK built the HP55C as a street-strip 383 stroker at 500 hp and 505 lb-ft of torque, running Dart SHP aluminum heads with 72cc chambers and 2.02/1.60 valves, and cautions up front that it can idle rough and may not suit a power-brake or air-conditioning setup.

Who this engine suits

Scat's H-beam rods, forged from 4340 steel, bolt to a matching 4340 forged Scat crankshaft, under forged pistons at 10.2:1 compression. ATK's parts list for reaching 500 hp includes an Edelbrock Performer RPM Air-Gap intake and a 750 CFM mechanical-secondary carburetor, built around a bigger cam than ATK's milder 383 stroker engines. Confirm which parts ship physically installed with us before ordering.

What to check before you buy

• ATK cautions it can be rough at idle and might not pair well with power brakes or AC, given the cam used here.
• This combination wants a noticeably higher stall-speed converter than ATK's street-tuned 383 engines; ask us for the exact number before choosing a converter.
• Fuel of 91 octane or higher is called for at this compression and cam combination.

Common questions

Will this work with power brakes or AC? ATK says it may not, given the idle characteristics of this cam.

What's the recommended stall speed? High, well above what ATK suggests for its street-tuned 383 builds; ask us for the figure.

What's the compression ratio? 10.2:1, the highest static compression in ATK's 383 stroker lineup. California requires BAR compliance for engine swap installations.