All a guess without actual dyno results for the 312 based entry but I was shooting for a score between 2.0 and 2.16 and claiming 317 cubic inches. I don’t have a lot of dyno values between 2500 and 3500 rpms for the Y combinations so I had to estimate those but the Y’s have typically been strong on the low end. The measured cubic inch for the Y entry is 315.73 so I had considered claiming 316 but by claiming 317 cubic inches, I was allowing for a 0.001” in checking variance for both the bore and stroke measurements at teardown.
The 427 entry I have has a running score of 1.9 but that’s on gasoline and with weak 2500 to 3500 rpm numbers. This is a standard bore 427 with a flat tappet cam, 10.4:1 compression ratio, factory 0.290” domed pistons, tunnel port heads, and running through a set of 2 1/8” tube chassis headers. Headers with 2.00” tubes would definitely be a help here but I don’t have a set sitting loose. This was the only combination I could put together in a hurry and have something that would still fit the rules. The E85 fuel has ended up being a show stopper on my end though.