It depends a lot on what you intend to use your Motorcycle Engines for. If you are going to be using the Motorcycle Engines solely for installation on motorcycles, then used Motorcycle Engines may do already (though if you really want to splurge, new ones are even better.) But what if you were going to place the Motorcycle Engines in cars (rather than car engines)? How would that work out?

Actually, this is already being done by many car assembly hobbyists. Usually, the cars to be powered by Motorcycle Engines are just small cars whose size and weight specifications are proportional to the power output of the Motorcycle Engines. As far back as the 1940s, the Cooper Car Company had been undertaking this practice - to make race cars, at that. Even BMW had tried doing that too in the 1950s. Though the general public may be ignorant of this trend, motorcycle and car assembly hobbyists know this practice works and with relatively good results. Their creations might be known as motorcycle/car hybrids.

The motorcycle/car hybrids are probably still being built today in someone's backyard with better results than those experienced back in the 1940s and 1950s – all because modern day Motorcycle Engines are stronger, faster, and better engineered than their early ancestors. Thanks to the decades of research done on how to improve Motorcycle Engines, hobbyists are reaping better rewards from their hybrid assembly efforts.

However, just because it looks like a car, runs like a car, and seems to behave like a car doesn't mean your motorcycle/car hybrid is automatically allowed on public and private roads in your country. The fact that you are using Motorcycle Engines to power the hybrids may be breaking the law for motor vehicles at some point (especially if you are one of the first to make and try to run these types of hybrids in that country.) So, unless you have some kind of special permit to run your hybrid on public and private roads, you may have to confine use of your Motorcycle Engines-powered hybrid vehicle in special areas only (like in a private racetrack or in an enclosed private family compound.)

If you are attracted to the idea of building motorcycle/car hybrid vehicles powered by Motorcycle Engines by yourself, be forewarned that the process actually entails quite an all-encompassing knowledge of how Motorcycle Engines work, how cars work, and how you can bridge any differences in the engineering of both or either with your own creativity and resources. A very smart mechanic/hobbyist can probably learn from manuals and prototypes alone – but for the less experienced and less talented hobbyist, full-time tutelage under someone very experienced in creating motorcycle/car hybrid vehicles might be more appropriate. There's no shame in asking for experienced guidance (except maybe to your ego) and in the end, you may get better results that way.

Equally surprising is that companies have been established throughout the world which concentrate on creating such motorcycle/car hybrid vehicles, many for racing. It might benefit you if you did research on how these companies do their work before you set about creating your own motorcycle/car hybrid vehicle.