Saito had some of their earlier production engines that were a really high compression ratio. This caused some backfiring in some circumstances. In subsequent models, they ran a lower compression ratio, which made them easier to run/tune without the same worry of backfiring. I have one of the later models which I think has a "G" stamp on the mounting flange. I don't know what letter they are stamping on the current production engines. ("A" indicates first production model, B, C, etc.) Beautiful engines!