The time is probably faster with "Hi" because the extra downforce gets the drive wheels back on the ground sooner. When your car is flying the wheels aren't pushing anything, so minimizing flight in the LC can help. It is still a bit surprising that this helps more than the wing drag hurts elsewhere, but there's a reason track cars and offroad racers try to get their wheels down. Great result and super-creative idea!
well the wing drag on this scale is effective as in drag race. Remember that air drag is not linear with speed, it's exponential. Mini4WD are around 40kmph. And this "Hi" system or this sucking air from under the car is so effective it is even used nowadays. The new electric car is called McMurtry Spéirling uses this fan system and I believe it can go 0-100kph in 1.4sec but most importantly the cornering on that car was insane. It grips the ground at insane speeds.
I think the answer probably make something Hi to open up way faster, by watching this video on 8:13 currently it takes 4 frames or 0.13 sec to open up, maybe try to cover the opening the side of Hi (left and right) so the air that sucked up by propeler isn't all wasted to all direction maybe put some cover on the side that can be folded up like light paper but folded up into pleat fold, and maybe mount it higher, taller mount spoiler in racing cars usually meant more downforce more responsive/faster pressure buildup at the top. Anyway i like your progession, good luck!
A variable pitch propeller system that actuates at the crossover would be the ideal system except for the tiny mechanical arrangement that would be required. I expect the gears would have to be metal. And the actuation would have to be by a stabilization control system. But, that would provide a faster response than changing the RPM on the fan. But then, a fan speed controller would be required to maintain RPM as blade pitch changed. Variable pitch is is how most propeller driven systems work along with rotor systems and helicopters as well.
