We often see references to 75%, 65% or some other percent of max power setting. It's easy if a pertinent chart/reference has the correlated RPM setting, but many do not. When there isn't an RPM setting, it is completely frustrating. For example, if your max RP is 2700 RPM, 75% power is NOT 2025 RPM. It's actually 75% HP - which makes sense - but how do you calculate that? It would seem if 2700 was 100% HP, 2025 would give you 75% HP...but it does not.
In studying engines and this problem, I've come up with a possible equation to calculate your percentage RPM settings. I underlined "possible" because I haven't correlated it to every engine. It goes like this - and it's pretty simple:
- Subtract the percentage from 100, multiply by 10, subtract from MAX
- Example: 75% of 2700 and 65% of 2700
- 100-75 = 25 x 10 = 250. 2700-250 = 2450 RPM (75% RPM)
- 100-65 = 35 x 10 = 350. 2700-350 = 2350 RPM (65% RPM)
I hope this helps. This question has bothered me for quite some time and it's a question students ask.
- FIG -