Ok they are both standing on the scale but it ONLY reacts once the right side is "activated". To me this is screaming different fuels used and diff density of said fuels allowing u to run more power for a given volume (per gallon)...
so this chart below shows density of gas is 6lb/gal...while pure ethanol (glowing yellow, yellow iv bag...CORN is yellow) ...is 6.6lb/gal...e85 is 6.5lb/gal...t
https://www.engineeringtoolbox.com/alternative-fuels-d_1221.html
The 7.1lb seems to be suggesting total added density for a volume of fluid...but a full tank ..20g would be +12lbs....not 7.1...+10lbs if e85....maybe they are thinking u run 1/2 a tank at the track??
I think I'm on the right track but not quite sure how they exactly get 7.1lbs...
to get the 7.1lbs right (assuming a full tank) we need a fuel with a density of 6.3-6.4/gal which is roughly E65 ..which i know doesn't exist...)
Find that density tho and that's what it likely runs on....