Display Percent Power on a G3X for a 914?

No experience here, but ...

The wild card here is probably the compression ratios.
Have you tried just selecting each of the Turbo options and seeing which of the numbers look more reasonable if different at all?
All engines that burn a set amount of similar fuel at a given RPM and MAP are going to produce very close to the same amount of power.
It is just physics and chemistry.  No Magic is involved.

That's an interesting idea.  Maybe I'll give that a shot if Garmin doesn't have a good answer.

Thanks!

In the absence of fuel flow data, one can achieve similar (approximate) results using manifold pressure and rpm. If one knows those two values at max power and the value of that max power, then an estimate of power at other values will scale (approximately) by MP x RPM. (Engines are fundamentally an air pump). Missing, but included in automobile fuel injection tables, is the cylinder filling efficiency. Also missing is the A/F ratio (lambda) (included in car ECU's) which can vary a lot. The latter is also the stumbling block for using fuel flow to estimate power output.

Rotax claims 912 ULS fuel consumption to be 0.48 lb/hp/hour (quite a crappy value, LyCons can get down to 0.40 and cars can be as low as 0.33, BTW). But still, AFR varies.

With proper charts provided by the manufacturer, old tech can provide pretty good numbers, though. (I don't yet know if Rotax has provided enough information - a Winter project to find out). One can distill down the provided data to provide useful cockpit guidance. He's mine for my old IO-360 Mooney. First, calibrated RPM numbers since the installed tach isn't all that accurate. Next, one decides the desired % power and which of the RPM & MP combinations to use. Next one reads either the "best power" or "best economy" chart to get fuel flow. Note there are, with a controllable prop, many ways to get the same power with considerable differences in fuel flow.

I do have fuel flow, so I just wish the G3X would do the calculations for me....  I'm surprised they don't have a Rotax option in the engine config page.