Most builders are not concerned with E/I ratios unless a tuned Intake/Exhaust system is required. It's only one piece of the puzzle, but an important one. When I order collectors from Jack Burns at least 81% average is desired for a properly designed functioning system. The hard part is to find a head that is at least close to this percentage; otherwise, a very expensive custom port job will be required to produce desirable E/I ratios. I was able to get in the "ballpark" with the Arias LS Hemi Heads when I was building the EFI AH427LSX for Nick Arias a few years back. We got roughly 79% E/I out of the box with the CNC ported versions.
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