google "atkins cycle engine". It was originally in a MRM build decades ago & they used very high compression & a special cam to bleed off enough psi to run regular gas with a phenomenal increase in gas mileage in a chebby truck (dont remember if it was a SB or BB but iirc it was BB). The trade off was a loss of mid/high range power. Something about the cam timing events that gave the benefit of high squeeze but lowered the actual CR so as not to ping & that sounds conflicting but that's what the deal was so yeah check it out & go from there. I'd like to do a 318 mileage build with it