ATK HP89C-EFI Chevy 350 with Fitech EFI 390HP

ATK pairs a FiTech Go Street EFI system with its 350 long block on the HP89C-EFI, bringing the combination to 390 hp and 420 lb-ft of torque once tuned in. The throttle body, wiring harness, and handheld tuner ship with the engine, so most of the fuel-injection hardware arrives already sorted.

What you still need to add

No fuel pump ships with this package; run either an electric pump or a mechanical pump paired with a FiTech Fuel Command Center. The EFI throttle body also needs a separate ignition box to fire, something easy to overlook when budgeting for the swap. Plan those two items in before the engine arrives.

Inside the long block

ATK's own aluminum heads use 2.020-inch intake and 1.600-inch exhaust valves with billet aluminum 1.6-ratio roller rockers, above hypereutectic pistons at 10:1 compression, paired with a double roller chain for timing. Displacement is 350 cubic inches. A dual-plane intake and HEI distributor round out the package, and the FiTech throttle body carries up to 400 hp of headroom beyond the engine's own rating.

ATK's break-in call is conventional 10W30 with a zinc additive mixed in for the first 3,000 miles, after which 91 octane fuel keeps it happy.

Pricing out a standalone EFI kit usually means separately sourcing a throttle body, a harness, and a tuner; here they arrive as one matched set.