Friday, April 24, 2020

Percent Power

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 -

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