Project Aprilia SR50: 100 mpg Madness Part 1, Basic Bolt on Stuff

 Aprilia SR50 Project bike

Project Aprilia SR50: 100 mpg Madness Part 1, Basic Bolt on Stuff

By Mike Kojima

A few years back, if you rode a scooter, most people would immediately write you off as a dork or some sort of lame PeeWee Herman sort of deviant. With rising gas prices, scooters have started to become an interesting alternative to cars, especially in urban areas as they are small, easy to park and their automatic transmissions deal with traffic and other urban hassles with greater ease than a motorcycle's manual transmission. They are also amazingly cheap to insure. With practical necessity, scooters are becoming more accepted and are quickly becoming fashionable transportation among urban hipsters with a culture all their own.

Read Part 2 here!

pee wee herman you are a giant dork

Perhaps you have seen the MotoIQ approach to scooter culture if you have been reading our exceedingly popular Project Ruckus series. We took a pedestrian 50cc Honda Scooter and turned it into an urban assault vehicle capable of taking on the toughest urban commuter traffic. In other parts of the world Scooter Tuning is a huge market, perhaps bigger than the car tuning market in this country. At MotoIQ, we want to bring you some of this continental culture to show that you can tread lightly but still have fun. Modding a scooter is cheap compared to a car and having economical back up transportation means that you can take more time to build your car correctly or park it for awhile if it is costing you too much to run instead of having to sell it.

Our new two wheel project is a very unique machine; it is an Aprilia SR50, perhaps the most advanced scooter on the market. It uses a hi tech, Orbital engine which combines the compactness and power density of a two stroke engine with the fuel economy and low emissions of a tiny four stroke. The Aprilia engine uses licensed Orbital technology which is basically An ECU controlled, directly injected, stratified charge two stroke. Two strokes by nature produce pretty low NOX emissions due to their low operating cylinder pressures but are terrible for hydrocarbons as they tend to blow raw fuel out the exhaust port on overlap.

Aprilia orbital engine

On the Aprilia’s Orbital engine, an electronic fuel injector puts the fuel directly into the combustion chamber after the exhaust port is closed, eliminating hydrocarbons blown out the exhaust port. The fuel is atomized by a burst of electronically metered high pressure air from a crank driven air pump. The burst of air and fuel is disbursed to a rich zone located around the spark plug. This rich area is easily ignited and helps support combustion in the leaner remainder of the cylinder. With this lean-burn system the Aprilia engine can run at air/fuel ratios as lean as 25:1 and can safely run as lean as 16:1 even at wide open throttle.  Unlike other two strokes the fuel is completely kept out of the crankcase so the amount being metered into the engine is precisely controlled with no uncontrolled fuel wetted areas. This greatly helps emissions and fuel economy compared to conventional two strokes.

Aprilia Orbital direct injection system


  1. This is awesome, I’ve been wanting to own one since 2010, and I just had a chance to own one, now looking at your build and reading about it, wants me to do that to my sr50… thanks for the right up

  2. Hi,
    i put the same exhaust on my Aprilia Sr50 2009, (stock 50cc)
    but its backfiring when you try to maintain the speed, i not sure what it can be ?
    do you had the same problem and you dix it?

Leave a Reply

Your email address will not be published. Required fields are marked *