Hi FB, The gears are 373:1 for now.We have the corn gas in this county but next door they still sell 91 oct. minus the corn, at least that's what we're lead to believe. Just a short ride but,there's a rather long stretch of straight country road where we do some WOT tests. rc-12yc that has been suggested sounds like a start. C61cx or ngk5671a-9 too maybe ?? Alot will depend on the type of driving. Today,,isn't like 1964 when I kept it at WOT all the time ! And, we had some Great pump Gas. Thanks everyone, D.y