Looking at a parts manufacturer website, they list various STC'd modifications for Mooneys with estimated (cruise?) speed gains for each.
However, I've heard that those gains are not additive. For instance, if you applied three mods with 5mph gain each, the total gain would be less than 15mph.
Is there a way to calculate what the gain should actually be if you applied several at once, assuming the gains listed are accurate when applied in isolation?
Most appear to be aerodynamic improvements (i.e. reducing drag) but a few are engine improvements (i.e. increasing thrust). I'd prefer an answer that addresses both sides in an integrated way, if possible.