In the town I grew up in as a teenager a local mechanic built a two wheeled motorcycle around a Corvair flat 6 cylinder engine. He stopped entering it into wild bike competitions because he always won. Darned if I can find any pics in my personal photos or on-line. Not at all practical - the exhaust pipes coming out the bottom of the cylinders had very little ground clearance, meaning they scrape on anything more than the littlest banking.
My dad asked him once how fast it would go. The guy admitted, "I got it up to 105, and was afraid to go any faster!"