More show and tell ,Mac 10-10 righty

[Al Smith]

First is the porting which I'm not certain how to explain .It uses three grooves which are not open ported but you can't really call then closed ports .They unload through a windowed piston and blow the transfer in at different times and different volumes as the crankcase pressure varies .Direction is above the intake of course .
I'm not certain what could be done to improve them so like all 10 series I just leave them alone .

 

[Al Smith]

It's been said things that run extremely fast usually don't run extremely long ,as was this example .
Around early 80's we cut firewood on the week ends .My dad and I had Mac PM 610's,dad worked his over a little bit which I now own .
My brother in law tried every thing he could to try and out run us ,even tried a Stihl 042 that couldn't get the job done .Then he had a plan .
Ah 10-10 righty with rocket fuel .either 100 octane av gas or Cam 2,forgot but pepped up with 20 percent nitro .My heavens did it run, reved up like a model airplane engine for about ten minutes and never ran again .A sacrifice to the piston gods evidently .

 

[wcorey]

First is the porting which I'm not certain how to explain .It uses three grooves which are not open ported but you can't really call then closed ports .They unload through a windowed piston and blow the transfer in at different times and different volumes as the crankcase pressure varies

I'd call that side fed open port, though in a bit of an unusual configuration with the triple ports.
Husqvarna 42/246 and 268 as well as Mac sp81 come to mind as examples in dual port.

To me the bridge between the upper and lower trans openings are what define closed port as opposed to open.
Either can be side fed or bottom fed with only the side fed requiring a windowed piston.