Re: 93 octane in stock engine
On the 305, check the operation of the EGR valve, it controls cruise detonation along with NOX reduction (emissions). If not hooked up or if the passages are plugged, this could be the cause, along with too much vacuum advance on earlier motors. Most low compression engines will run better on regular. Chrysler issued a TSB relating to high octane fuel and volutility issues. Modern gasoline by law has to contain detergents to keep fuel systems clean.