Flow rate of injectors

The value 163g/min seems very high if we know that in average the engine takes 18lts/hr. 

18000 x 0,7 / 60 / 8 = 26 gr/ min.

Is the value 163g/min for continuos "open" operation ?

Yes, I assume that the injectors are ROTAX branded Bosch items (like much other stuff)). Bosch define/categorize the through-put by grams of Heptan/min (full open) at 3 bar.
No injectors of open for more than a fraction of time during the sucktion rotation of the engine 

One way to look at this is using the BUDS dongle and Rotax software. There you can see how many miliseconds each injector is open, so you can compute the work cycle of each injector, and obtain the "open" equivalent.

Let's suppose maximum consumption is 35 lts/hour then

35 * 0,7 / 8/ 60 = 51 gr / min, 

and, let's suppose the work cycle is 50 %, then your injector fully open is 51 / 0,5 = 102 gr/min

I assume that the ECU that controls the timing & opening time of the injectors is based on a specific max flow rate. It does not work to use injectors with different specs ... the same goes for cars. Selecting injector based on assumption is a no-go in aviation.