7.4v would be a two cell lipo--they run 3.7v each.
My thinking for lipos was that a single cell would probably be close lap time wise to a "normal" 4-cell car, off-setting the reduced voltage with the substantially reduced weight allowing higher corner speeds and quicker acceleration/deceleration. Another field-leveler might be running the two cell lipo with a 55-65 turn lathe motor. Not surprising they're a rocket with a "normal" motor as you're pumping even more voltage into it than we had in the heyday of 6-cell 1/12 way back when...with a way better motor today.
That said, I'm opposed to lipo's in cars. There's WAY too much to go wrong (like burning down your house around them) for the "average" car racer to keep track of.
Scottrik