Join Date: Aug 2010
Location: Hudson Valley, New York
Bronco Info: 1978 Bronco 9" lift, 35s, Cummins power
With a small cam and iron heads, 9.3:1 would do best with 93 octane, unless you retard the timing slightly, which will negate the efficiency benefit of the higher compression.
Ox, with iron heads and a truck cam, 10.5:1 will ping unless you retard the timing. My Mustang motor has 10.95:1 with aluminum canted valve hi-swirl heads and a big solid lifter cam. ( 250/260 duration @ .050" ) and it barely gets away with premium gas. Of course, the more aggressive the cam, the lower the cylinder pressure at low rpm and the less octane required. Vice versa for smaller cams.
1978 Bronco 9" lift on 35s, with 1991 Cummins 6BT swap, Denny T fuel pin, pump mods, 3200 gov. spring, Trac-Loc front diff, C6 built by Dynamic Transmissions with billet 1200 rpm converter, 4" exhaust, no muffler. GOT TORQUE?