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working out compression ratios
About half of the 1A38 heads I have are undated.
(10-10-2018, 11:43 PM)Tony Press Wrote:  
Casting number 1A 670 was introduced under Part Number BC 82 in August 1933 with a slightly raised compression.

Casting number 1A 684 still under Part Number BC 82 appeared sometime before 1936.

So far I can't see a 1A 7** head number on the cards or parts books. 

Sorry Tony and Ian  - my 7-something was first look at a bad casting number. It is ambiguous but must be 1A 670, and is dated 12.11.(193)4 and is also marked "AF1T". So 1A 684 (marked "AF2T) must have come in later than that.. and certainly before 12.4.(193)5 which is the other head I have sitting here. Can others' collections narrow that down?

My naive/basic water filling experiments re-performed with a D16 Champion give:
1A38 with taps 40cc
tap hole is approximately 1cc
new Ricardo with space for high lift valves 30cc
1A 684 35cc
1A 670 about 37cc

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