Quote Originally Posted by Lol Moore View Post
I have recently been reading all i can find about transfer ports (more interested in PCP though) and have some thoughts:

the idea of a venturi is an interesting one (I get involved with them in my work) but here I dont think you could get them to work as its the increase in velocity through the narrowing of the venturi that produces a pressure drop at that point and thus creates suction which is used to draw more air, here you have an initial increase in pressure with little or no flow so air would pass put of the venturi, which means you would need a pretty efficient none return valve on the suction leg?

One thought that did occur to me is why can you not have a small cylindrical secion on the end of the piston that is sligthly smaller than the port so that it fills the port as the piston reaches the end of its travel which means no where for the air remaining in the cylinder to go so cushioning the piston may be it could seal maybe it could be sized to create some air passage?

I have also been reading some conflicting info on polishing the ports, I assume this is done to "ease" the path of the air? there is some thinking that this is a bad thing as it leads to laminar flow whereas turbulent flow is preferable? what about a rifled transfer port to impart spin to the air?


Been working on this idea for the last month with some interesting results. Still work in progress as I have still to get through various combinations of length/diameter and shape of 'rods' that enter the port. Using a nose extension with 4mm hole in center to accept threaded rods. My TP is 3.9mm dia and initially started using M4 nylon bolts reduced to 2mm for fear of a nasty thwack and one knacked compression tube. Am confidently using M4 brass bolts now and have had them full length of transfer port at 3.4mm in dia.
One reason I wanted to do this was to try and work out where the piston stops and hence cylinder gap. Another reason was to see if I could eliminate bounce on ultra light pistons. Results thus far indicate, on my TX, the piston stops somewhere around 1.8 to 3 mm but need to do further tests. Also want to try with different strokes and piston weights - so many variables! One 'rod' I tried changed my aim points quite substantially at the longer ranges, accuracy bombed after about 30 yds so shape is another headache!
Anyway, it's all fun and keeps me busy when the telly is crap or kids/wife doing my head in!