ATK HP74 Chevy 350 Vortec 1996-2000 Truck Base Engine 315HP

The HP74 is a Vortec-style 350 long block built for 1996-2000 Chevy and GMC trucks and SUVs, rated at 315 hp and 400 lb-ft of torque. ATK tested it on an engine dyno running an aftermarket EFI system, so real output depends heavily on the fuel and tuning setup you pair with it. The one step you cannot skip This engine needs its ECM tuned and headers fitted to reach its rated output, and ATK warns plainly that skipping the tune can damage the engine. Treat a calibration appointment as part of the swap budget, not an afterthought, since the combination is built around that tuning step rather than around bolt-it-in simplicity. What is inside Cast iron Vortec heads turn a 1.5 rocker ratio through stamped-steel arms, feeding hypereutectic pistons that hold 9.3:1 compression under a single roller timing chain, a lighter-duty chain than the double roller chains ATK uses on its higher-output engines. Bore is 4.040 inches and stroke is 3.480 inches, for 350 cubic inches total. It is a new build rather than a core exchange, and ATK recommends 91 octane fuel or higher once the tune is dialed in. Q: Can I run this without tuning the ECM first? No; ATK states that skipping the tune risks engine damage. Q: What vehicles is it built for? 1996-2000 Chevy and GMC truck and SUV applications.