ATK HP89M Chevy 350 Mid Dress Engine 390HP

Somewhere between a bare long block and a fully dressed carbureted engine sits ATK's HP89M mid-dress build, a new 350 small block putting out 390 horsepower, with a dress level that leaves the carburetor and a few finishing pieces for the buyer to add.

What "mid dress" leaves for you to add

No carburetor comes mounted on this version; ATK's build sheet points toward a Quick Fuel 680 CFM unit, paired with a Holley mechanical fuel pump, to finish the fuel side. Heads on this build use straight spark plugs, and flexplate bolts are not included, so budget for both separately before final assembly, along with 420 ft-lbs worth of torque to plan your driveline around.

What is bolted on

This iron-block 350 arrives with its aluminum cylinder heads, double roller timing chain, billet aluminum roller rockers, HEI distributor, and water pump already fitted, running a cam ground to the 220/224 duration profile on a 110 LSA. A 2200-2800 stall converter and 34-36 degrees of ignition timing are called for on the build sheet, with 91-octane-or-higher fuel recommended throughout. Chassis fitment follows the same pattern as the rest of this engine family: the rear-sump pan is a poor match for a Chevelle with steering linkage behind the crossmember, a handful of Corvette years, and 62-67 Chevy IIs.

Common questions

Does this come fully dressed? No, it is a mid-dress build; the carburetor and fuel pump are recommended parts rather than installed items.

What's the torque rating? 420 ft-lbs.