The Holley 4165, 4 barrel carburetor features:
Single fuel inlet.
Side mounted float bowls.
Primary metering block.
No secondary metering block.
Mechanical operated secondaries
Front and rear pump diaphragms.
Mechanical operated secondaries.
Designed to fit the spread bore type of intake manifold, but with an adapter can be fitted to a square bore type.
The Holley 4150 has a secondary metering block. The 4165 only has a primary metering block.
The Holley 4165 carburetor throttle body has 2 large vacuum ports. The front port is for the PCV valve. The rear port is for the power break booster. The remaining vacuum ports will deliver full vacuum to whatever device is needed.