I seem to remember 72 degrees being the "reccomended" number. When I was running my DMW typhoon I had extreme vibration troubles, It was so severe you could not see! I asked several experimental engineers from both Ford and Jaguar about it. The general impression was that there was no data as no one had made an adjustable crank. For once I had a trump card, This bike had two engines connected by a splined coupling in the centre. The first attempt was to change from 180 deg to 360. (both together. It sorted the vibration, but was a pain to start as both compressions occured simultaneous. It took for men about 25 yards to bump start it. Next step was 45 deg ureka it was the answer, several other permutations were tried, by altering the angle I could move the vibration along the lengh of the bike. 70 odd degrees was not a good number for this application. Alex George who was riding it for a while reckoned that I beat Honda to the big-bang engine by at least 6 months.