Stock bottom end 318. Lunati cam .470/.489 lift 259/269 advertised duration. 302 closed chamber iron heads, deck shaved. 025. 1.88 intake valves. Calculated cr is around 9.6:1. Getting mixed reviews on what octane I should run. Also this is a tbi engine. No knock sensors, 160* t stat. It's in a 91 d150, auto.

 

87 should be fine, if you get more spark knock than you can tolerate, bump to 89.

 

I'm having trouble finding the cc of the closed chamber heads. I read they were 63, but I read a magazine article that they were 53, lol. If they are indeed 53 them my cr is around 10.1:1. Still ok with 87?? Guess if it pings I'll go to 89 octane.

 

Give it a shot, see what happens. If you get too much ping on 87, dump some octane booster in there, then switch to 89 on the next fill-up.

 

Trial and error I guess. Only way to find out is to do it. Too many mixed reviews on the subject to know for sure. I tried Google, found a graph that showed anything over 9 was to use 110 octane. I know that's not right, lol. Bunch of people disagreeing on iron heads compared to aluminum, different degree thermostats, blah, blah, lol.