And higher octane fuel will often cause the fuel level in the bowl to be too high, causing the engine to run rich.
A hundred years ago, Stromberg specified float adjustment settings if using higher octane than for which the engine was designed. Generally, Stromberg would specify an "initial" setting based on the octane, and a final fuel level setting. Generally the initial setting would be close, but the level setting was the one desired.
Those old low compression engines were much more forgiving on settings than modern ones. If the settings were worth changing on 6.0 compression engines, certainly worth checking on more modern engines.
A good "rule of thumb" is the needed octane number should be about 10 times the compression ratio. If I remember right (and if I didn't, someone will point it out
), higher compression 235's were 8.0 to 1, whereas the lower compression 7.5 to 1.
Thus 75~80 octane should be about right.
EDIT: the post by Otto above is correct, if real gasoline:
87 octane has 117,600 BTU/gallon
91 octane has 117,600 BTU/gallon
93 octane has 117,600 BTU/gallon
and (if you can still find it)
Sunoco 260 has 117,600 BTU/gallon
Jon
