Search on google for honda grom engine swap. There have been a few that have done it. Most regret doing it though, as the head aches it causes far outweigh any benefits. Some people switched to a cbr125r motor. It has six speed and you can get racing cams for it. The motor makes around 13hp stock. But with mods and race gas maybe 18 hp? That would double the hp of the Grom and give you six gears. Fitting a CBR250R engine into a Grom - Page 5 - Honda CBR250R Forum : Honda CBR 250 Forums
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