675 ,315,178 and 920 all flow pretty much the same, talking 2 cfm diff. Chamber shrouds more on the closed versions..as expected. I can flow the 302's i have again...but nothing makes me believe they flow any different.
The funny thing about the early 273 heads is they jump + 9 cfm (178 cfm) at .400 lift compared to 675 (169 cfm) using your numbers and others. Then they drop back down to about equal (174 cfm) with 675 (171 cfm) heads at .500 lift.
