Bill wrote:
Quote:
Veering a little off topic - CWB mentioned the price of 87 octane, and it reminded me of a question I've had for a long time. Does anyone actually use any gas other than 87 octane these days?
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I do...sorta. Here in Colorado Springs, the octane of "regular" is actually 85, mid grade is 87, and super premium is 91. This is because of the elevation (6500) with its lower atmospheric pressure, and associated lower combustion chamber pressures. However, I find my Jeep 4.0 will knock on dry days in normal driving with the 85 octane regular so I routinely use 87 (mid grade) (atmospheric water vapor is pre-ignition (knock) suppressant).
But when I'm going to tow the TM up the mountain grades going out of town on a hot, dry day, I've found that premium (91) is a necessity to prevent knocking until I get up to around 8500 feet. Apparently the sustained full throttle operation is getting something in the combustion chamber (carbon deposits, most likely) hot enough that I'm getting pre-ignition.
My Jeep is old enough that it apparently doesn't have a very sophisticated engine computer that automatically retards the spark when knocking occurs...which is just as well as that also cuts power.