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I like the way it is.
You have the choice of whether to use it to get by traffic (especially on in/out laps) or save it for a fight at the end or just blow it all on a banzai lap.
Having it available every lap would reduce the strategic aspect and make it pointless imo.
Gonna agree with I B that it is more fn having a whole set of it for the whole race instead of recharging every lap.