That will depend on the setup. My 9.7:1 340 (no vacuum advance, 34 total, 91 0ctane/10%e) will cruise as lean as 15.4 with no surging. But 15.8-16.0 and it will start surging. I don't like to go leaner than about 15.2 to be safe. I am currently changing the ignition box and swapping to a vacuum advance distributor, so I will have to test the mid 15's again. But once again, it depends on the setup.
1970 YO7 A66 [Canadian Export] F8 Challenger 340 (Currently in shop for stroker assy.)
