455 heads

[Bryan C. Robertson]

What is the purpose of these small ports?

[Smartin]

Those are exhaust crossover ports.  Many people plug them like this to keep hot exhaust gases from going under the carb.  It also helps keep the paint on the intake from burning off.  It may effect the ability of the stock choke to work well, though.

[Bryan C. Robertson]

Thank you!!

[LARRY70GS]

The exhaust crossover ports are blocked off with screw in plugs in that photo.  Their function is to heat the corresponding passageway under the intake to help with fuel vaporization in cold weather.  A hotter intake though can hurt performance and make vapor lock more likely in hot weather.  Blocking the passageways in the heads results in a cooler intake and better performance at the expense of cold weather operation during warm up.  It also makes the stock choke inoperable because the exhaust crossover also heats the pocket in the intake that operates the thermostatic choke coil.

 

The smaller holes for each cylinder are for the Air Injection Reactor ports.  Air from an air pump is injected into the exhaust to continue the combustion process for lower emissions.  On the 72 intakes, there is a passageway on each side for the AIR pump.  Those holes in the head can be plugged with cup plugs or screw in plugs.

 

See page 67-8 in the 1972 Buick Chassis Manual,

 

https://www.teambuick.com/reference/library/72_chassis/files/67-a.php

 

https://www.v8buick.com/index.php?threads/a-i-r-heads.380626/#post-3336052

Edited February 7, 2023 by LARRY70GS (see edit history)

[Smartin]

Thanks for clarifying Larry.  I guess I didn't think that he might have been asking about the small air holes that aren't plugged.