V12 engine numbers

Talk about the E-Type Series 3
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#1 V12 engine numbers

Post by lowact » Thu Aug 02, 2018 4:51 am

I’m trying to understand V12 engine numbers, in particular the suffix’s. Can anyone suggest?
My engine numbers are: Etype (US spec) = 7S6333SA, XJ12 (UK spec) = 7P55161HB. What I’ve interpreted so far:

1st character, number 7 or 8: dunno, maybe the works that produced them?

2nd character, P or S: Seems E-types and XJS engines had “S”, limo’s had “P”. I can’t imagine why there would be such distinction in an engine number?

Remaining numbers probably the engine serial number, do I have the 6,333rd 7S and 55,161st 7P engines?

Second-last character is the compression ratio: L = low compression (7.8:1); S = standard compression, (9.0:1); H = high compression. Initially (1980) high compression was 10:1, in 1981 it was 11.5:1 for US spec, 12.5:1 for UK spec? Subsequent 6.0L engines had 11.0:1, I assume they use “H” also?

Final character, I recall from somewhere, has something to do with the piston/sleeve tolerances? I’d really like to understand this, as my plan is to fit the HE bits and efi+ecu from the 7P engine onto the 7S engine…
'72 OTS manual V12

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