Re: Would you like to help a bunch of teenagers go fast?
Welcome to the forum. I hope the advice given so far will steer you away from your original concept. If this in fact is a "class project" you'll want success. The mechanics involved with mounting an engine that size and transferring the power to the rear wheel will require a lot of design and fabrication skills. I concur that a simple 2 or 4 stroke kit will be a far better choice for you and your classmates.
As for "going fast", it is and will always be a bicycle. You have to keep in mind that what you're building will have bicycle wheels, brakes and bearings. 25 to 35mph is reasonable, especially for a first build. Reaching higher might be more than your skills and the bike is safely capable of of delivering. Keep it simple and keep it safe.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"