Hi Senne, Very interesting experimenting you are doing here.
Follows some of my own personal experiences.
A small engine least powerful lets you follow changes for more-or-less.
You do need to load verify your changed to not be fooled by “the subjective”.
An electrical generator would seem to be ideal for this. So I’d thought. Just measure the produced wattage lading capability.
Ha! And that is where for DIY fuel-gasses it falls down.
As Mr Til said well there are always many factors into play.
Electrical generation IS affected by changes in ambient temperatures, local humidity greatly on the small systems. Small electric generators by their nature are portable. Sea level to mountains pass level; or Inland Empire out here far- west is 4000-5000 feet for changing. Makes a difference!
So the tendency is to Standardized Conditions; Lab-Rat.
Good numbers then.
Numbered performances; unrepeatable in 90% of real world conditions usages.
So all-in-all your 12hp mobile riding mower is REAL conditions testing.
Just set up somewhere a power needing up-slope timed test for your before/after changing comparisons.
DOers always have my Best Regards
tree-farmer Steve unruh