ATK HP98 Chevy 350 Base Engine 345HP

Producing 345 hp and 400 lb-ft of torque, the HP98 is ATK's bare 350 long block, built on a cast iron OE-style core rather than the roller-block design ATK uses on its higher-output stroker lines. It ships bare of carburetor, intake, and ignition, ready to finish to your own spec.

Recommended parts, not included

ATK's suggested combination for this engine pairs a Weiand Stealth dual-plane intake with Champion spark plugs and a 680 CFM Quick Fuel carburetor running vacuum secondaries and an electric choke. None of these ship with the base long block; they are simply the parts ATK dyno-tested it with.

Inside the long block

ATK cast iron heads turn stamped-steel 1.5-ratio rockers above hypereutectic pistons holding 9.1:1 compression, run by a hydraulic roller camshaft, a double roller chain for timing, and a high-volume Melling oil pump. Bore and stroke come to 4.040 and 3.480 inches. For break-in, 3,000 miles on conventional 10W30 oil with a zinc additive comes first, then 91 octane fuel for the long run.

Q: What comes installed versus recommended only? The long block, heads, cam, and oil pump ship installed; the intake, carburetor, and spark plugs are recommendations, purchased separately.

Choosing the bare long block over a dressed version makes the most sense if you already own a carburetor, distributor, or intake from a previous build and simply need a fresh 350 underneath them.