I have heard that there are two different versions of the 48s. The ones used on 350 HOs had smaller chambers, according to this information. See Dragncar's post above about 65cc chambers. The ones that came on the 400s and 428s were spec'd at 72cc. I don't know how much supporting evidence there is for that - how many 350 HO heads have been CC'd and documented vs. heads from the larger engines? We all know Pontiac was fudging the compression numbers a little and certain heads had slightly bigger or smaller chambers than others.
428s used the same heads as 400s and came from the factory with dished pistons to keep the CR the same.
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'72 Formula 400 Lucerne Blue, Blue Deluxe interior - My first car!
'73 Firebird 350/4-speed Black on Black, mix & match.
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