Project Aprilia SR50: 100 MPG Madness Part 2, Engine Internals



Malossi Ditech full circle crankshaft
The main power improving feature on the Malossi Ditech crank on the left is the full circle counterweights.  These take up more physical room in the crankcase increasing the primary compression compared to the stock crank on the right.  This helps improve a two stroke engines volumetric efficiency.  The Malossi crank is also made of higher strength materials, uses higher quality bearings and has better balance than stock.  If future development allows us to reach 12,000 rpm, this crank can easily take it.

We also obtained a Malossi full circle high primary compression crankshaft. The Malossi crank has full circle counterweights. These full circle counterweights take up more physical volume in the crankcase increasing the primary compression. This is a trick two stroke tuners often do to improve the engines volumetric efficiency and scavenging, particularly at high RPM. The crank has better balance than stock with heavy metal inserts and is made out of superior higher strength materials so it can be safe up to 12,000 rpm, although it is currently not possible to spin a Ditech engine this high. One counterweight has a machined in eccentric to properly drive the Orbital systems air injection system’s compressor. The only disadvantage of the Malossi crank is that it is heavier than stock and will rev a little slower.

Before assembly, we sent the cylinder, piston, rings, and piston pin to WPC Treatment to have these items subjected to WPC’s revolutionary friction and wear resisting process. You can read about how WPC works here.

For our engines assembly we went to Technosquare. Howard Watanabe discovered that the Malossi cylinder was pretty mismatched to our engine case and some time was spent match porting the case to the cylinders transfer ports. At this time Howard also checked and set our squish clearance which in two stroke lingo is piston to cylinder head clearance at 0.6mm which required machining 0.50mm from the cylinder deck surface leaving us with a final compression ratio of 13:1.

motul motocool coolant
We like the fact that Motul Motocool coolant is pre mixed.

Our engine was reassembled with and the Malossi ECU installed. We coated the cylinder walls with Motul 710 two stroke oil and refilled the cooling system with Motul Motocool pre mixed coolant.  We also ran clean burning 100% synthetic Motul 710 oil in the oil injection system. We fired up the engine, allowed it to come to operating temperature at fast idle, bled the cooling system and ran the engine for 20 minutes with no load. We then shut the engine off and allowed it to cool, rechecked the cylinder torque and went for a ride.


  1. hello, I own an Aprilia SR50 2009 carburettor scooter. This post is about the DI injected model.

    Will this kit work on my scooter? Or should i be looking at something else? Im guessing the ECU won’t do much on mine!

    I want more power!

    1. This kit will not work but Malossi and Polini makes kits especially for the carburated versions of this engine. They make even more power too!

Leave a Reply

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