Quote:
Originally Posted by mrtexas
Not necessarily true. The old leaded premium was 100 research octane. 93 super today is (87 motor + 99 research)/2. When unleaded gasoline came out they added the motor octane method to simulate city driving. High research octane doesn't guarantee performance in the city. Remember back in the day that some gasoline would cause cars to "run on" after the key was turned off? Minimum motor octane cures that as well.
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Engines did not "run on" because of the fuel octane level. They "ran on" because the valve ports were so full of carbon which was subsequently heated when driving. Shut the engine off and that hot build up of carbon would ignite the furl vapors.
I recall all too well doing valve jobs back in the early 80's... most heads took a LOT of efforts just to get all of the built up carbon chipped away enough so I could sand blast the heads prior to machining. that stuff (carbon build up) was HARD and very difficult to remove.