boost ports ?

Are they worth doing ? should they be angled steeply up and narrow and lower that the main transfers? A nice cooling effect for piston or just paper filling theory ? I should ad that my interest is in piston ported 175 ,

A good question Dan,
By boost ports do you mean `grooves 'in the cylinder wall fed through piston holes, as in a Rex barrel, or something more resembling conventional ports/ducts but on a smaller scale? Or indeed something different altogether!

Trevor

I mean a small window opposite the exhaust, being fed via a hole in the piston. At amlost bdc. A nice angle up to squrt over the mains and plug the exhaust a little with fresh charge n I can't help thinking it'll have bother being piston ported and with an open carb sitting right behind it maybe the charge could be sent right b ack up the carb. With the exhaust forces acting on it , for a moment the whole thing would be in alinement leaking crank pressure exhaust and inlet .....makes me wonder

I think you have probably answered you`re own question here Dan. Very tricky to incorporate safely in a piston ported barrel, at least in meaningful size. Many years ago I replicated the arrangement used in the old, early MT Honda. I cut a port in the liner and milled a recess horizontally round to blend with the transfer ducts with just enough metal left to seal from the inlet. The barrel had a similar groove machined in just shy of breaking through. I think the upward angle was 55*, but don`t think of trying to blank the exhaust port with gas it won`t comply and just disappear into the pipe, and connecting to the inlet duct that also won`t work without a reed valve in place.
Anything that gets more mixture into the cylinder can help pick up power, and cool things a little.
125s are more challenging because you can do so much more to them and having a machine shop to hand makes it all very convenient. Particularly if you go to a reed and water cooling, and you`ll make more power any way!

Trevor

Ohh for a reed valve ,

This might be an option, championship winning concept!