One thing that should be done is do new corrections on engines either the old engines should be corrected to the Dyno Correction SAE J1349 which is to 29.234 Baro & 77 degrees. The old Correction SAE J607 is to 29.92 & 60 degrees. This would reduce the old engines by 4%. Or you could just add 4 % to the new engines
http://www.land-and-sea.com/dyno-tec...horsepower.htm
Look at this web site on dyno corrections.
Need to get all engines rated at the same weather correction.