I suppose I could mix up some toulene (sp) with 93 or make the trip down to the ZAZZ! station and fill up with 100 leaded. If I was to set it up to run on pump gas what do you think is the most compression I could get away with? I was favoring the 400 over the 350 or 383 because everyone has a 350 and it made a little more power. What are the disadvantages of siamesed bores?