I have 2 951 engines. I am thinking about a billet head for one of them. I have one with 49cc domes for a bore of 89.5mm. SD spec for domes is 51.8 +/- .6. For a slightly modified engine is 49cc too small? I want to run 91 octane. Per ADA, the 50cc dome the compression is 155 and for 48cc its 172. I would guess 49cc would be about 160. Is this too much? Should I find 50 cc domes?