2-Stroke Power Barbie Jeep
When I was little I wanted a power-wheels electric jeep more than anything in the world. I never got one. But later I decided to make my childhood dream a reality. If an adult riding a power-wheels wasn't ridiculous enough already, I chose a pink barbie jeep to sweeten the deal.
Acquiring the Chassis
Craiglist is always coming through for me. This time it was an electrically dead pink jeep chassis for free.
There was no way the plastic would hold up an adult's weight for very long and more importantly, I needed something to mount axle bracketry to. I decided to make a simple frame out of small square steel tubing.
Although a small 4-stroke engine would have been ideal for this application with low torque, my budget didn't have much room. Luck had it that I had a spare 49cc pocketbike motor laying around... similar to the one shown. The really tricky part was finding an exhaust that would work with the engine exhaust port and that would somehow fit under the jeep. The effect and placement of the expansion chamber on a two stroke exhaust is imperative to power output. The resonance of the exhaust gas off the chamber wall acts as a form of acoustic supercharging by reverberating backwards and compressing intake air that was drawn all the way through the chamber into the exhaust pipe back into the chamber. This compresses more air into the chamber and leads to a more powerful explosion. The shape and placement of the chamber for optimal power requires extensive tuning and with small engines like this one, it can really hurt power output to mess with that tuning. Unfortunately sometimes you've got to take a hit somewhere and so I chose the least destructive method I could come up with. I picked an exhaust with a long run to the expansion chamber so that i could bend the constant radius pipe to fit under the jeep and leave the chamber sticking out the back.