Compression

[Straight6]

What compression ratio should I use in a 302 or a 289 if I want to run low octane unleaded gas?

 

[Seabronc]

All Ford small block engines are designerd to give satisfactory performance on 87 octane according to the owner manuals. However, my 351 4bbl actually gets better milage using 89 octane. I never have done a cost comparison, so the little extra milage might not be worth the expense with todays prices of gas. I get about 4 mpg more on 89 when on the road by letting the truck drive itself using cruise control.

Probably the stock 302 engine 8.5 to 1 to answer your question.

Good luck,

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[Broncoholics]

If you're talking # per sq in. then 150 - 160 is normal.