In the Engine Analyzer programs, what is the advantages and disadvantages of going higher than 75% on the Total Exh/Int %?
The 75% number has been developed from experience over the last 60 years or so. Taylor from MIT developing aircraft engines in WWII was one the first to come up with this # that I know of. If you have more than 75%, it does NOT means you should restrict the exhaust. It does mean that there is probably more benefit to enlarging the intake valve at the expense of the exhaust valve. Since a bore only allows an intake and exhaust valve combo so big, there usually must be a tradeoff. If you make the intake bigger, the exhaust must get smaller. This 75% (85% for nitrous oxide or supercharged) is VERY general, and reported for info only. It is not used in the program to predict performance, as those calculations are much more detailed.
