Hi,

I purchased a 66 mustang with a 302 4 valve engine (year is 1978). The dealer said to use 93 but the only ethanol free fuel near me is 90. Will using 90 instead of 93 damage the engine?

thank you

 

Yes it will damage your engine. You don't need ethanol free 93 as most gas stations have 10% ethanol fuel. You'll be fine with standard 93 octane gas that has 10% ethanol. Or get some octane booster like Boostane and use their mixing chart to get 93 octane.