MOPED ARMY

I thought about this too, but it looked like the ports in the malossi just run deeper in to the casting, and are plenty big to move all the volume that the actual ports on the piston could let through. In fact, I found it more necessary to enlarge the ports on the piston.

not sure about that other cylinder, but on my polini the 'open' W boost ports are much shallower, it's just a difference in design, routing it right around the rings and piston crown in stead of deeper in the cylinder.

Very interesting. Is that a 46mm piston? Did you go wider on the piston? Or just down? Are you saying making a Polini W port deeper, wouldn't make much difference?

I have more questions :)

I also want my next project to be, making this:

Look like this:

i suppose making the boosts bigger (deeper) on a polini can't hurt, as long as the port in the piston is big enuf..

that's the 43mm/65cc piston there, my 46.5mm/73c one has a normal skirt wall, with the small window cut above the piston pin and the larger one next to it like that, but the whole skirt is not recessed/cut out like that, and there is no re-inforcement webbing from the pin to the skirt to make it like that.

i just opened up the holes in the piston, brought them up to the webbing that goes from the pin to the crown, and extended the cut outs in the cylinder skirt to match them. Mainly about 5-6mm to the left, if you're looking from the bottom of the cylinder, on one side, a bit less on the other, where like half of one of the larger windows in the piston was blocked. i just went a few mm in and ramped it over to the main port passage.

I cleaned up the transfer and boost ports in the cylinder too, but did not want to enlarge too much, as not to loose too much intake charge velocity, since this was going on a stock-mod (poor man's speed-engine) case first, and there's plenty of port there for a 13mm carb.

Also opened up the exhaust to the max so i could stick my finger all the way in it. it's kind of scary filing around the cylinder stud hole.

have more pics at home, can post some if you want.

it's torquey, got killer accel, and eats hills (and belts).

yeah, different piston design in the two kits, and of course the diameter. I focused on the upper ports that feed through the piston. the lower cutouts in the skirt i just shaved the outside of the edges down to be more earodynamic, since i had plenty of port passage outside the skirt after i matched my case, you only need the openings to be as wide as the bottoms of the main transfers in the case anyway, so hold it in each case half and see how it matches up to that more importantly.

check out the vids i posted in the 'how to make a vespa fast' thread for inspirations.