Re: 2v 4v heads
The 2V and 4V identifies the number of venturis the carby has. A 4V(4 barrel) drops about 1.5"WG while the 2V is about 3"WG. The 4V tends to have less open and smaller chambers .
The 289 4V was made from 1964 to 1967. 54.5cc chambers. Smaller intake valve (1.67") than the 302 (1.78")
The 302 4V can easily be mistaken for the 289 head and was only made in 1968 (53.5cc chambers). The 302 2Vs were 63cc until mid 1969 when they dropped to 58.2cc. Then in 1977 the chambers went up to 69cc until the eighties, when you get the E5 and E7 series heads.
The 351 4V was only made from 1969 to 1971. Both the 4V and 2V had 60.4cc chambers. The 2V got smaller 302 sized valves in 1978.
The pistons, compression heights, etc were matched to each type to maintain design CR.
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