The conversion to full power started today.... Here is a photo of the non-PAL (under 500 fps) and full power valve stems.... They seal on a plastic (Delrin?) seat inside the valve housing that is 0.171" diameter....



The plastic spring seat is pressed into the end of the valve against the large flat end in the photo.... Because it is shouldered and fits flush, it is difficult to remove.... I therefore filed a flat in each side big enough to get the blade of a small flat screwdriver into to pry it out.... as this won't be the last time I take the valve apart....

Here are the port measurements and areas....

Hole in plastic spring seat 0.196" (larger than the ID of the spring)
ID of the valve spring 0.171" (which limits the flow into the valve)
ID of the valve seat 0.171" (area 0.0230 sq.in.)
OD of the non-PAL stem 0.153" (area 0.0184 sq.in.)
Remaining throat area with non-PAL stem 0.0046 sq.in. (equivalent to 0.077" D)
OD of the full power stem 0.100" (area 0.0079 sq.in.)
Remaining throat area with the full power stem 0.0151 sq.in. (equivalent to 0.139" D)
Six exhaust ports measuring 0.105" D each (total area 0.052 sq.in. - over twice what is required)

The conclusion is that (at least in theory) more air can get into the valve through the spring than can get out through the valve throat, which is the limiting factor to airflow in the valve.... From previous experience, the wasted volume of the six exhaust ports and the groove connecting them affects the efficiency, but that is the subject for later experiments.... Later today, I hope to shoot some string with the gun in it's "stock" full power form....

Bob