well to run 2 2s's in series you would ned a new ESC, and a motor capable of running them. Problem is those parts are 1/8th scale territory so the ESC alone wouldn't even fit on the chassis.
Also the motor would be so large you would have to make some custom mount, and gear it so high it wouldn't be funny. Finally you would need to custom create some drivechain as the stock revos would more then likely snap, and the diffs would would become a metal puree. Ohh and while you are at it you would need to find some way to power it as the lipos that fit in the chassis wouldn't be able to drive the motor/esc combo you would need, and would probably instantly puff up from being overtaxed.
So to sum it up if you can't figure it out you basically would need to replace your whole vehicle with a 1/8th scale RC
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