Valve mod, 50+ FPE!

[bikincrazy52]

I had an extra talon valve laying around and decided to polish, port, and tweak with it. I bored the stem out to 3.2 mm, polished everything to a mirror finish, bored the valve spring retainer, and bored the inlet holes on the valve stem.

Here are some numbers with a small 13 cu in tank, with kodiaks.

Fill pressure was 3300 pounds, hammer weight 70 grams.

1.1062
2.1055
3.1052
4.1025
5.1015
6.1018
7.1006
8.1001

That is almost 53 FPE.

That was with everything set to max airflow, so shot count suffered. But damn, this thing totally jacked up my spinner target!
😯

[knifemaker]

Good looking numbers. 😀 Bbl. Length?

[shrpshotr28]

gotta love kodiacs. Did you note the ending pressure?

[bikincrazy52]

It was a 24″ barrel and ending pressure was 2600 psi. I still cannot figure out why velocity starts dropping off when I still have that much pressure left.

Here is a pic taken with a Crosman premier hollow point, 14.3 gr.

I finally got to hear a sonic boom 😛 My first airgun that could even come close to that with a standard weight pellet.

[jkaleido]

hello bikincrazy52 🙂

I admire your work a lot 🙂 and would be very interesting to publish photos to share your experience in those mods

sorry for my english

thanks

[kejano25]

sweet

[marc]

Your velocity starts dropping so soon becouse your hammer is to heavy for the valve. Yes it can push hard. But you have a 60fps drop in velocity in eight shots. I can get a 60shot string with just 30fps drop! Try lightening your hammer in stages of 10 gram.

Regards,

Marc

[bikincrazy52]

Thanks. However, I was going for maximum velocity on this test. I will tone it down to start at 1000 fps, and see what I can do.

[cygnus-x-d82]

yup too much hammer, or too high spring preload…

i find the rifles run best if the hammer spring preload is just enough that it will open the valve at max pressure, i dont turn it up highger than that…for me its 6.5…..rest is adjusted with tophat travel distance and valve return spring.

i was runnning my SS valve bored out to 3.3mm, return spring just touching the delrin not really helping in closing it, as little valve travel as possible…so it starts to leak around 1100 psi….thats ok with me

however….i get 65 fpe with 42 grain EJ, and a stock hammer with a brass hammer weight that just lisghtly longer than the original hammer weight

i shot it this weekend in .22 12″ config at 32 fpe, and it was dead on for about 40 shots ! i must say i was very impressed with the accuracy of the rifle, squirrel targets at 100yards was not that much of a challenge…12″ barrel !!!!

im gonna dial the return spring in to it helps lose the valve though…it will bring the power down a notch, but might be better for air useage wich is quite high considering i got an 800cc tank on that rifle

[oney01]

How many CC’s is the stock tank? How many fps do you consider tight?
About how many tight shots should one expect to get from a stock tank, modified valve at about 40 foot pounds (18″ .22)?

[Anabel Roark]

Have someone tried Bulk Ammo deals with free shipping at Ammo Board?

[Author]

Posts