ATK HP90 Chevy 383 Vortec Marine Base Engine 345HP

The HP90 is a marine-specific 383 long block making 345 hp with 445 lb-ft on tap, its bearing clearances and camshaft profile set up for sustained marine loads rather than street driving. ATK is explicit that this combination is not intended for automotive use.

What marine-grade means here

The intake is a marine-grade dual plane, the distributor and spark plug wires are marine-grade, and the recommended carburetor falls in the 650 CFM range. These are parts chosen for a boat's heat and vibration rather than a car's underhood environment, and none of them ship installed on this base engine.

Inside the long block

Dart Vortec cast iron heads carry a 1.5 rocker ratio in stamped steel, above hypereutectic pistons holding 9.5:1 compression. Scat supplies the rotating assembly, a nodular-iron crank and I-beam rods bolted up with ARP hardware, turning a 3.750-inch stroke inside a 4.040-inch bore for the 383 total.

Conventional 10W30 with a zinc additive covers the first 3,000 miles of running time on a marine engine like this one, and 91 octane is the fuel ATK specifies after that.

Q: Can I put this in a car or truck? No. ATK designed the bearing clearances and cam profile strictly for marine use.

Because it is a base-dress build, budget time to source a matching carburetor, distributor, and fuel delivery system before the boat goes back in the water.