ATK HP291P Chevy 350 Base Engine 325HP

The ATK HP291P is a classic-tuned Chevy 350 base engine rated at 325 hp, built with a milder hydraulic flat-tappet cam instead of a roller grind, keeping enough vacuum signal to run power brakes and other vacuum accessories without trouble.

Who this engine suits

Cast-iron heads with 1.94/1.50 valves sit over hypereutectic pistons at 9.1:1 compression, tuned for everyday street manners rather than peak output. This is a bare long block: induction, carburetor, distributor, and water pump are not mounted, and ATK lists them only as suggested parts for the builder.

A few details to plan around

• The dipstick location is on the passenger side of the vehicle, worth noting if you are swapping this into a car that originally used the driver side.
• Oiling runs through a high-volume Melling pump.
• Break-in oil is conventional, with a zinc additive recommended for roughly the first 3,000 miles.

Common questions

Will this run power accessories off vacuum? Yes, the flat-tappet cam here is milder than ATK's roller-cammed stroker engines, so vacuum accessories are not an issue.

Is the carburetor included? No, only the base long block ships; induction is left for the installer.

Where's the dipstick? On the passenger side of the vehicle, so check that against the side your current engine uses before you order.

What cylinder heads does it use? Cast iron, with 1.94/1.50 valves, tuned for street manners rather than outright output. California requires BAR compliance for engine swap installations.