We took the 920s on my 273 and worked them over. Did pretty much the same with a 302. The 302 flow and velocity went down so we did something it didn't like. I stopped on my 920s when I got 169 cfm average, with 116% port velocity just by smoothing things out especially around the base of the guides and a decent valve job. I also installed stainless valves 1.84/1.58