Okay so lately ive been working on some improvements to the ever popular 40-50cc chinese air cooled cag motors. This is the first of many mods that will be in my finished race engines.
As they roll out of the factories in quangzho in their millions they are an okay unit. Reliable in operation but wildly varied in final tolerances and power. Usually they supply about 2-3hp and top out at about 8000-9000rpm
The main thing to remember about these engines as that they are based largely on an agricultural engine. So they never needed to be particularly powerful to begin with and were optimised to run reliably at a certain rpm for an extended period of time - pretty well the opposite to what we want in our race bikes - so the transfer port setup and induction setup isnt particularly suited to generating huge revs and power. Time to fix that!
probably the best thing we can do on an otherwise stock cylinder for power is to add whats known as a boost port. A boost port is a third transfer passage for air charge to enter the combustion chamber in combination with the two main transfer ports. Basically it helps scavenge the back of the cylinder and provites better charge purity = better power. roughly 10 - 20% plus allowing more revs.
I started off with a stock two piece head kit from HK motos as the prototype for testing because it already came with a single boost port added which will be the best for piston ring life (this type of port setup is rough on the piston rings so you dont want to run too many boost ports). As you can see it is all but useless.
The depth of the port is less then 1mm so the air flow is through it will be next to zero, and the height of the boost port is totally insufficient. With the piston at bottom dead center the port isnt even uncovered.
Easily fixed with the mill however! this one has been bored to the correct depth with an end mill and to the appropriate height. You will notice ive left the top of the port roof flat for now as i intend on comparing the power difference between having it flat and having it angled. The angled roof will obviously be better but i am curious to see just how large the difference will be! The height of the boost port itself is also another item up for testing.
4 Barrels are now complete with different port secifications so i will test all on the same engine to find which works best and get the complete engine dyno'd and post the results. stay tuned!
Should be up for sale in the near future in 2 piece and single piece guise.
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