ATK HP32M Chevy 350 Vortec Mid Dress Engine 350HP

The ATK HP32M is the mid-dress tier of ATK's 350 hp, 400 lb-ft Chevy 350 Vortec, sharing the same hypereutectic 9.5:1-compression pistons and Vortec valve sizing, 1.94/1.50, as the complete HP32C build.

What mid-dress means here

Balancer, intake manifold, HEI distributor, and water pump are installed, but the carburetor and fuel delivery, plus the plugs and wires, are left as ATK's suggested parts rather than installed hardware, which puts this a step ahead of a bare long block.

What to check before you buy

• Ignition timing on this build runs through the vehicle's PCM rather than a distributor adjustment, so the ECM needs to be tuned for this cam.
• Camshaft and timing chain specs match the complete HP32C; the difference between the two is which parts ship bolted on.
• A vacuum-secondary carburetor with electric choke is ATK's recommended part here, not installed hardware.

Common questions

Does the computer need reprogramming? Yes, ATK calls for ECM tuning to match this cam and head combination.

Which parts are bolted on already? Balancer, intake, distributor, and water pump; the carburetor and ignition consumables are not.

What's the torque rating? 400 lb-ft, paired with 350 hp.

How is this different from the complete HP32C? The complete build adds the carburetor, fuel pump, spark plugs, and plug wires that this mid-dress version leaves for the installer to supply.