Originally Posted by Tbuck
I believe there is a passage way between the upper and lower tube that needs to be drilled also. Otherwise, just modifying the valve will be pointless. Some of the other more knowledgeable folks on here can tell you more.
Valve modification can help even without the entlargement of the hole. But because the airflow will be after the valve still limited width the hole between tubes, there are borders what you can not cross without the hole entlargement... especially when that what you will are more shoots above ~240 fps - the combination of the short 6" barrel and small airflow is here limitation (with longer barrel, for example in P68SC, the valve mods can improve the performance more).
But more than valve mods can make here hammer lightening - because with valve mods you commonly only improve the maximal flow of valve, but to be able use it for better economy, you need reduce the dwell time... and eliminate the bouncing - what is hard to do without lighter hammer.
But on other side, to be able get good velocities with really very light hammer (below 25 gram... stock weighs ~42 grams) you need likewise the to have great airflow = large hole between of the tubes.
So there are three steps:
- entlargement of the hole
- valve mods
- hammer lightening
(+ spring modding, but that is more likely part of final velocity adjustment)
When you do them in good way, the they will work for you even separately. But when you join them, the difference will be a lot bigger. Normally 1+1+1=3 but here 1+1+1=111.