ATK HP107M Chevy 383 Stroker Mid Dress Engine 525HP

The ATK HP107M is the middle tier of ATK's 525 hp, 515 lb-ft 383 stroker, running a 4340 forged Scat crankshaft spinning Scat H-beam rods, sized for the loads at this power level, under 10.2:1 forged pistons.

What mid-dress means here

The head castings are Dart aluminum, 70cc combustion chambers, with valve sizing of 2.02/1.60. Balancer, intake, distributor, and water pump are bolted on for this build, leaving the carburetor, fuel pump, and ignition consumables on ATK's recommended list for the installer. A single-plane manifold feeds the induction side rather than a dual-plane design.

Parts the installer still needs to add

• The carburetor and fuel pump are not mounted, named only as ATK's parts suggestions.
• Spark plugs and plug wires are likewise left out of this build.
• Flexplate and flywheel depend on your transmission and are not part of this build either.

Common questions

Is the carburetor mounted on the engine? No, only the intake, distributor, water pump, and balancer are installed on this build.

Does it include a flexplate? No, flexplate and flywheel depend on your transmission and are not part of this build.

How does this compare with the base HP107? It is a step up in installed hardware, running the same 10.2:1-compression combination.

What camshaft does it run? The same hydraulic roller grind ATK uses across its 525-hp 383 stroker family. California requires BAR compliance for engine swap installations.