O-320 (No suffix) later redesignated O-320-A1A
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1.
Provisions for a controllable-pitch propeller and 25-degree spark advance.

O-320-A1B
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1.
Same as A1A but with straight riser in oil sump and -32 carburetor.

O-320-A2A
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1.
Same as A1A but with fixed-pitch propeller.

O-320-A2B
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1.
Same as A2A but with straight riser in oil sump and -32 carburetor.

O-320-A2C
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1.
Same as A2B but with retard breaker magnetos.

O-320-A2D
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1.
Same as E3D but with conical mounts.

O-320-A3A
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1.
Same as A1A but with 7/16" prop bolts.

O-320-A3B
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1.
Same as A3A but with straight riser in oil sump and -32 carburetor.

O-320-A3C
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1.
Same as A3B but with retard breaker magnetos.

O-320-B1A
160 hp (119 kW) at 2700 rpm, Minimum fuel grade 100/130 or 91/96 avgas, compression ratio 8.50:1.
Same as A1A but with high compression pistons.

O-320-B1B
160 hp (119 kW) at 2700 rpm, Minimum fuel grade 100/130 or 91/96 avgas, compression ratio 8.50:1.
Same as B1A but with straight riser in oil sump and -32 carburetor.

O-320-B2A
160 hp (119 kW) at 2700 rpm, Minimum fuel grade 100/130 or 91/96 avgas, compression ratio 8.50:1.
Same as B1A but with fixed-pitch propeller provisions.

O-320-B2B
160 hp (119 kW) at 2700 rpm, Minimum fuel grade 100/130 or 91/96 avgas, compression ratio 8.50:1.
Same as B2A but with straight riser in oil sump and -32 carburetor.

O-320-B2C
160 hp (119 kW) at 2700 rpm, Minimum fuel grade 100/130 or 91/96 avgas, compression ratio 8.50:1.
Same as B2B but with retard breaker magnetos.

O-320-B2D
160 hp (119 kW) at 2700 rpm, Minimum fuel grade 91/96 avgas, compression ratio 8.50:1.
Same as D1D but with conical engine mounts and no propeller governor.

O-320-B2E
160 hp (119 kW) at 2700 rpm, Minimum fuel grade 91/96 avgas, compression ratio 8.50:1.
Same as B2B except the carburetor is in the same location as the O-320-D models.

O-320-B3A
160 hp (119 kW) at 2700 rpm, Minimum fuel grade 100/130 or 91/96 avgas, compression ratio 8.50:1.
Same as B1A but with 7/16 inch propeller bolts.

O-320-B3B
160 hp (119 kW) at 2700 rpm, Minimum fuel grade 100/130 or 91/96 avgas, compression ratio 8.50:1.
Same as B1A but with 7/16 inch propellor bolts, a straight riser in oil sump, and -32 carburetor.

O-320-B3C
160 hp (119 kW) at 2700 rpm, Minimum fuel grade 100/130 or 91/96 avgas, compression ratio 8.50:1.
Same as B3B but with retard breaker magnetos.

O-320-C1A
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1.
Low compression version converted through field conversion of B1A.
O-320-C1B
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1.
Low compression version converted through field conversion of B1B.
O-320-C2A
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1.
Low compression version converted through field conversion of B2A.
O-320-C2B
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1.
Low compression version converted through field conversion of B2B.
O-320-C2C
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1.
Low compression version converted through field conversion of B2C.
O-320-C3A
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1.
Low compression version converted through field conversion of B3A.
O-320-C3B
150 hp (112 kW)
O-320 (No suffix) later redesignated O-320-A1A
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1. Provisions for a controllable-pitch propeller and 25-degree spark advance.
O-320-A1B
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1. Same as A1A but with straight riser in oil sump and -32 carburetor.
O-320-A2A
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1. Same as A1A but with fixed-pitch propeller.
O-320-A2B
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1. Same as A2A but with straight riser in oil sump and -32 carburetor.
O-320-A2C
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1. Same as A2B but with retard breaker magnetos.
O-320-A2D
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1. Same as E3D but with conical mounts.
O-320-A3A
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1. Same as A1A but with 7/16" prop bolts.
O-320-A3B
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1. Same as A3A but with straight riser in oil sump and -32 carburetor.
O-320-A3C
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1. Same as A3B but with retard breaker magnetos.
O-320-B1A
160 hp (119 kW) at 2700 rpm, Minimum fuel grade 100/130 or 91/96 avgas, compression ratio 8.50:1. Same as A1A but with high compression pistons.
O-320-B1B
160 hp (119 kW) at 2700 rpm, Minimum fuel grade 100/130 or 91/96 avgas, compression ratio 8.50:1. Same as B1A but with straight riser in oil sump and -32 carburetor.
O-320-B2A
160 hp (119 kW) at 2700 rpm, Minimum fuel grade 100/130 or 91/96 avgas, compression ratio 8.50:1. Same as B1A but with fixed-pitch propeller provisions.
O-320-B2B
160 hp (119 kW) at 2700 rpm, Minimum fuel grade 100/130 or 91/96 avgas, compression ratio 8.50:1. Same as B2A but with straight riser in oil sump and -32 carburetor.
O-320-B2C
160 hp (119 kW) at 2700 rpm, Minimum fuel grade 100/130 or 91/96 avgas, compression ratio 8.50:1. Same as B2B but with retard breaker magnetos.
O-320-B2D
160 hp (119 kW) at 2700 rpm, Minimum fuel grade 91/96 avgas, compression ratio 8.50:1. Same as D1D but with conical engine mounts and no propeller governor.
O-320-B2E
160 hp (119 kW) at 2700 rpm, Minimum fuel grade 91/96 avgas, compression ratio 8.50:1. Same as B2B except the carburetor is in the same location as the O-320-D models.
O-320-B3A
160 hp (119 kW) at 2700 rpm, Minimum fuel grade 100/130 or 91/96 avgas, compression ratio 8.50:1. Same as B1A but with 7/16 inch propeller bolts.
O-320-B3B
160 hp (119 kW) at 2700 rpm, Minimum fuel grade 100/130 or 91/96 avgas, compression ratio 8.50:1. Same as B1A but with 7/16 inch propellor bolts, a straight riser in oil sump, and -32 carburetor.
O-320-B3C
160 hp (119 kW) at 2700 rpm, Minimum fuel grade 100/130 or 91/96 avgas, compression ratio 8.50:1. Same as B3B but with retard breaker magnetos.
O-320-C1A
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1. Low compression version converted through field conversion of B1A.
O-320-C1B
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1. Low compression version converted through field conversion of B1B.
O-320-C2A
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1. Low compression version converted through field conversion of B2A.
O-320-C2B
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1. Low compression version converted through field conversion of B2B.
O-320-C2C
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1. Low compression version converted through field conversion of B2C.
O-320-C3A
150 hp (112 kW) at 2700 rpm, Minimum fuel grade 80/87 avgas, compression ratio 7.00:1. Low compression version converted through field conversion of B3A.
O-320-C3B
150 hp (112 kW) 
Lycoming O-320