Originally Posted by Desert Rat
Hobbs just ticks over .1 hours every 6 minutes. Some of them are wired to start ticking when you turn the master on, some are on a switch so they don't start until oil pressure comes up.
Assuming 'engine" time is the same as what the certified world calls "Tach time," it works like on a tractor or other random farm equipment- i.e. it ticks .1 hour every 6 minutes at full power but when you reduce r.p.m. it slows down proportionally.
Traditionally, you log hobbs time in your logbook but schedule maintenance by tach time.
Edit- I'm not talking specifically about your airplane, just industry standard.
To date, all my experience has been in the certified world and the above is exactly right. I flew a rental C172 this morning to stay proficient whose tach time was about 70% of the Hobbs time. All these reports of virtually identical hobbs and engine time mean that engine time is accruing too quickly for most people. If you religiously follow 100 hour maintenance, 500 hour mag, and 2000 hour overhaul rules, I think you will be early in all cases, incurring costs before they are really needed. If you can set the EFIS to use a % of max power calculation for engine time / tach time, you might extend parts' effective life per the schedule by 10-30%.