Mini Drag Bike

This project came about from wondering how fast I could make one of those little Chinese import pocket bikes go without doing a complete engine swap. I also wanted the project to look cool, have better handling, and sound much better.

Here is the original bike, straight out of the crate

I purchased a couple of pocket bikes and decided on using the yellow one for modifying. It came with a 50cc 4-stroke engine and was a fun, zippy little bike to begin with. A few modifications wouldn't hurt though.

The stock bike parked beside my Suzuki GSX-R 600 race bike

The bike is considerably smaller than a full sized sportbike, and it is smaller than a YSR as well. Not made for street legal riding, these pocket bikes are really for kids, big kids included

I don't have any good pictures of the construction of the parts for this bike. I do have some initial 3D renderings of the nitrous system though. It was designed in Solid Works and the parts were machined out for the system. Two of the different nitrous systems are show below.

Two can nitrous system

This is the 2 canister nitrous system 3D rendering.

Five can nitrous system

Here is the 5 canister nitrous system 3D rendering. The canisters are the type commonly used in whipped cream makers and are readily available. The puncturing devices feature a one way valve to keep back pressure from escaping when there is not a full cylinder in place. A 12 volt solenoid delivers the nitrous through a braided stainless line to the carburetor's air filter. The system is a fogger type, and as the nitrous flows into the carburetor, it pushes past the venturi and picks up the extra fuel for the engine.

Nitrous is not a flammable gas. It simply supplies more air for the fuel to burn. By doing this, more fuel can be supplied as well. More fuel means more power. The nitrous is stored in a compressed liquid form in the canisters. Think of the whole system as a liquid supercharger, or turbocharger, for the engine.

A few pictures of the finished bike are below.

Mini Drag Bike

Here is the finished bike. The aggressive stance makes this little bike look good. It is a blast to drive, and handling is improved over stock thanks to the extended wheelbase.

The swingarm is a one foot extension

The original placement of the rear tire was completely underneath the rear fairing, as can be seen in the photos at the top of the page. With the tire moved well back, it has that drag bike look.

The nitrous kit is a 4 canister model

The nitrous kit mounted to the bike is a 4 canister model. The canisters feed into the billet aluminum manifold block, and on to the stainless solenoid valve. Braided stainless steel hose connects the valve to the carburetor, and can be seen extending from the left of the solenoid valve and up into the side of the front fairing.

Basketed swingarm

The view of the swingarm here shows that it is basketed, meaning that it has the additional support running side to side for extra rigidity. Not visible are the blue lights that illuminate the underside of the bike at night.

Low, lean, and mean

After completion of the swingarm and nitrous kit, the engine was rebuilt and a larger carburetor was installed. The restriction devices were removed from the throttle assembly to allow for full throttle movement. With the restrictors in, the throttle could only be opened half way. The exhaust system was removed and all restrictions were eliminated. The pipes were brought up to a larger diameter, and the system was reinstalled. With the modified exhaust, the system runs 1 into 2, or 1 cylinder output to 2 separate pipes and mufflers. Having little or no restriction means more power output, and the exhaust note is now very low, mean, and loud. It is very loud, actually louder than my GSX-R.

So far, the top speed of the bike has been 70 MPH with my 200 pound frame on it. Although I had originally wanted to break the 100 MPH mark, I am happy with the outcome. 100 MPH might have been pushing the 10 inch tires as well. Since the manufacturer states the top speed of the bike is 30 MPH with restriction in place, I am happy with the results. I tested the bike with the throttle restrictors removed and reached almost 50 MPH with just a little tuning. Since the speed is most likely estimated by the manufacturer for a 100 pound rider, I think I did OK with the modifications.

All in all, this is a fun bike. 70 MPH this close to the ground is a scary experience though. Later, I may revisit this experiment and open the engine back up to install a lock up clutch on the CVT transmission and a smaller rear sprocket to see how fast I can push it.

Thanks for reading, and be sure to check out our other projects.

Russ W. Moore
Bad Brothers Racing