What is the calculation to determine horsepower increase or decrease in relation to RAD,, given that we have a known hp/rad base ?
To get your RAD you need baro, temp, humidity (or some related measure of moisture in the air) These can be used with online calculators for Density altitude or dyno correction factors etc. More or less HP goes up or down 3% per 1000ft of density altitude change. Get you close. Dyno correction factors certainly can be used as well, give you an answer. Online calculators for all those.
maybe this can help:
http://www.csgnetwork.com/relhumhpcalc.html