Posted by RDavis on Tuesday, September 25, 2001 at 0:30AM :
In Reply to: Octane Requirement posted by Mike Costello on Monday, September 24, 2001 at 4:41PM :
Depending on what year 251 you have, will determine whether it is the early 60's with 7:1 compression ratio or late 60's with 8:1 ratio. The higher the compression ratio, the higher the octane rated fuel you should use. Very high compression as in race cars and airplane engines require the use of over 100 octane rated fuel. There is no such thing as using a too high a rated octane fuel in your engine as it is just a rating of how stable the fuel will burn under high compression and heat conditions. High octane rated fuel is more resistant but low octane rated fuel is more subject to pre-ignition and detonation under high compression and heat conditions. Your 251 should run fine with any fuel at the pumps, 87-93 octane. The compression is low enough that 87 will run just fine under normal conditions unless your engine is running hot or you have found a way to raise the compression to 9:5 and up.
It should do no harm to run 104 octane rated fuel in the 251, it would be expensive and a waste but it would not hurt it.
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