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On 5 Mar 2001, at 21:38, Jedediah Millheiser wrote: > at 8.5:1? my S-10 blazer runs 8.75:1CR and only > calls for regular pump gas. > > i didn't think you needed premium until you hit at > least the high 9s It really depends on a lot of things, one of which is bound to be head temp. Since air cooled cars run higher head temps than water cooled cars, the EFFECTIVE CR of an air cooled engine is higher than it appears. I'm really not an expert on this. If you want really good info, get some of Gene Berg's papers on this subject. The CR of our engines was 7.7 up to 72, when it was reduced to 7.3. With today's gas even that's too high. Of course the CR is not particularly important when the engine is lightly loaded, but with wide open throttle the internal pressures reach their max and that's when knock happens and this will damage things. Really. - ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA ******************************* ------------------------------------------------------------------- Pitch in! Send your pledge of support! mailto:support@vwtype3.org