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I'd like to know a little more about the differences in the various Spit motors if it's not to much trouble. What were the differences beyond just displacement?
[/ QUOTE ]In short, the original Spitfire engine was 1147cc, derived from the then-current Herald engine (which, in turn, was derived from the 803cc and then 948cc Standard 8 / 10 engine). Bore / stroke was 69.3mm / 76 mm as I recall. These are notable for having the "six port" heads, with siamesed intake ports.
Spitfire Mk3s came with a 1296cc, eight-port head engine. Bore was increased on these to 74mm; stroke remained the same. The MkIV Spitfire used much the same engine, but with different ("commonised" with TR6/GT6) big end bearings.
Finally, the Spitfire "1500" is actually 1493cc, with the same 74mm bore and an increase in stroke to 87.5 mm (if I recall correctly). Nice for increased low-end torque, but the longer stroke might have something to do with the seemingly increased failure of big-end bearings that seems to curse these motors to this day.