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> lower-octane fuel burns *hotter*. JimA=> Not true. OK, tell me where I get off track: Octane is added to fuel to slow down the burn. This spreads combustion over time to apply power through more of the stroke. Lower-octane fuel burns faster, concentrating the expended energy closer to the spark. The burn is pushing on the piston for less time, so less energy is converted to motion of the piston, and more to heat in the head and chamber walls. Knock is eliminated when more of the burn takes place after TDC, and this is the primary benefit of higher octane, but there's also this element of combustion efficiency that makes a difference in terms of cooling that I at least believe I have perceived directly. Are you saying this is all just bunk? Steven Ayres, Prescott AZ '66 343 ------------------------------------------------------------------- Too much? Digest! mailto:type3-d-request@vwtype3.org Subj=subscribe