Balancing the flow within the Mutant valve
:ugeekn: Just had to go in after the success of the plenum mods to find out how balanced the flow was within the mutant valve.
Emptied the air and dismantled barrel / trigger group from receiver / air tube so I could unscrew air tank fitting from receiver giving access to valve body & poppet.
Valve & poppet in hand started measuring the throat & transfer passage sizes finding BOTH at @ .200″
Poppet stem is @ .118″
When doing the math on area of a .200″ hole ( This for Throat ) … we get an AREA value. ( * .0314 sq in )
Then we do the math on the area of the .118″ poppet stem … we get an area value. ( * .019 sq in )
SUBTRACT the area of Stem from the area of Throat … we get a value of whats left in Area to pass air around the two. ( * .0205 sq in )
NOW KEEP IN MIND THE transfer port leaving the .200″ throat is also .200″ all the way to barrel ( Which we’ll cover shortly )
In the case of the Mutant we have a pretty good restriction within the Valve throat when the .118 stem partially blocks it and WHY the practice of stepping down the diameter of poppets stem is a common modification trick :biggrinn:
In this case DID NOT WISH TO WEAKEN poppets stem by reducing its diameter making the stem more prone to breakage … so we address this by increasing the throat size just a little bit.
* In doing some math again for area gain required within throat the Diameter figured is .235″ having an area of ( .0426 sq in )
When we subtract the stem area of .019 sq in from the larger .235″ throat of .0426 sq in we end up with .0317 sq in of area to pass the air headed for the transfer port :biggrinn:
REMEMBER when we started with that .200 throat feeding a .200″ transfer port ( Area of .0314 sq in ) now with valve throat opened up to .235″ diameter with .0317 sq in of actual area past the stem … we now have a balanced flow within valves throat & no longer having any restriction throttling back the air flow & no need for a reduced diameter potentially fragile poppet stem.
:suprisedn: NOW TO MAKE THIS WORK we did need to rebuild the poppets head using a tougher material ( PEEK )
Was able to simply twist and pull off the white ( Delrin perhaps ? ) poppet head from the OEM stem so it could get reused.
The Diameter of the OEM poppet head was .265″ and we Kept it exactly the same with the PEEK replacement made.
* In looking at the OEM poppet head under a magnifying glass it was lightly dented already and would not have survived IMO asked to plug a throat just .035″ larger in diameter ( .0175″ per side which is not very much ) thus w/o even trying it just made up a Heavy Duty replacement.
Thats it for a few hours of fiddle time on the Mutant :8:
Scott
All Replies
This is just one Bad Ass little Pup …. love this gun :8:
It certainly is :8:
People sometimes forget about shotcount but it’s just as simple, end of shots end of fun!
Not to forget the last modifications were to simply change out the plenum spacer for one having more volume ( gained by thinner wall and a tad more length )
The volume of regulated air within plenum is the ONLY thing changed here other than hammer spring adjustment to find out what gains were made doing so.
So … HOW MUCH POWER did it make available ???
The rifle in stock form turned up had JSB 18.1’s doing @ 940 fps for a tad over 35 ft lbs.
Now with the larger plenum at the same setting the 18.1’s are doing @ 990 fps for a tad over 39 ft lbs.
For giggles while turned up ran some H&N Barracuda 21.1 grain with them doing 925 fps producing 40 ft lbs !
While rifles an air hog cranked up, this power setting is a full 1 3/4 turns more than I’m running at normally with JSB 15.9’s at 900 fps for @ 28.6 ft lbs.
Very flexible power range adjusted with simple hammer spring tension changes ;D
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An update on efficiency etc …
was out today taking a hike with my son who has a Cricket .22 pup.
We sat down on this side hill & filled BOTH our guns to 250 bar, loaded up magazines Then proceeded to bang away at some buckeye trees that still had Balls ( Seed Pods ) hanging on the branches.
My standard Mutant at 5 mags ( 60 shots ) still had @ 155 bar so i put threw a 6th mag ( 72 shots ) and then a 7th ( 84 shots ) where the POI at @ 40 yards remained unchanged !!! :suprisedn: … pressure reading @ 100 bar and from this point the POI did start falling away. * The first 60 shots has an efficiency of @ 1.42 FPE/cuin per shot
With the work done to valve & plenum the gun remained very stable as it entered self regulation at & below 140 bar with enough juice left to be an able small game hunter plinker for honestly +/- 80 shots with JSB 15.9s at @ 900 fps.
This is just one Bad Ass little Pup …. love this gun :8:
So went ahead and opened the barrel transfer hole to @ .195″ on an @ 10* angle just shy of bore contact followed up with a .125″ carbide burr elongating the hole forward @ .025″ at the same 10* degree angle creating a semi wedge / V shape port within the bore. Blended in with a high speed stone in the dremel tool then Deburred & polished leade & reassembling gun … We’re done :whistle:
can you quantify the results of your mod, please? Looking forward to some interesting gains.
Darryl
This last bit of barrel transfer work was to just Equalize the size & flow potential of transfer passage valve to behind pellet.
In the end at SUB max power levels we gained some efficiency. If / when leaned on for more power the valve will now flow BIG TIME and power to launch heavy pellets increased a bit.
As a professional tuner always looking / wanting the most from my air guns. Power if wanted and greater efficiency when you don’t :biggrinn:
That’s amazing! Thanks for the explanation, Motorhead.
Darryl
So went ahead and opened the barrel transfer hole to @ .195″ on an @ 10* angle just shy of bore contact followed up with a .125″ carbide burr elongating the hole forward @ .025″ at the same 10* degree angle creating a semi wedge / V shape port within the bore. Blended in with a high speed stone in the dremel tool then Deburred & polished leade & reassembling gun … We’re done :whistle:
can you quantify the results of your mod, please? Looking forward to some interesting gains.
Darryl
This last bit of barrel transfer work was to just Equalize the size & flow potential of transfer passage valve to behind pellet.
In the end at SUB max power levels we gained some efficiency. If / when leaned on for more power the valve will now flow BIG TIME and power to launch heavy pellets increased a bit.
As a professional tuner always looking / wanting the most from my air guns. Power if wanted and greater efficiency when you don’t :biggrinn:
So went ahead and opened the barrel transfer hole to @ .195″ on an @ 10* angle just shy of bore contact followed up with a .125″ carbide burr elongating the hole forward @ .025″ at the same 10* degree angle creating a semi wedge / V shape port within the bore. Blended in with a high speed stone in the dremel tool then Deburred & polished leade & reassembling gun … We’re done :whistle:
can you quantify the results of your mod, please? Looking forward to some interesting gains.
Darryl
Measured a fully seated JSB 15.9 finding skirt seated @ + .035″ ahead of the transfer hole. * BTW the 18.1’s having a shallower skirt cavity get seated deeper yet !
So went ahead and opened the barrel transfer hole to @ .195″ on an @ 10* angle just shy of bore contact followed up with a .125″ carbide burr elongating the hole forward @ .025″ at the same 10* degree angle creating a semi wedge / V shape port within the bore. Blended in with a high speed stone in the dremel tool then Deburred & polished leade & reassembling gun … We’re done :whistle:
Only had less than a week of shooting it sense & maybe @ 200 pellets down range to get a feel for changes so far.
A few things I have noticed ….
Valve dwell is shorter now and took adding just a tad more ( @ 1/8 turn ) spring pre-load to get back power to where previously.
* Reason for … is that as HP air passing by the poppet encounters less flow resistance within throat there is greater drop in pressure differential across the seat and valve closes up faster ( Less dwell )
The adding of some more spring tension aids in getting a tad more poppet lift and flow to raise the power back a tad.
In application tho the valves lower dwell is still using less air per shot due to the faster closing cycle.
Second and this due to less valve dwell is the shot noise is even quieter and the firing cycle feels a tad snappier too.
Scott
When all is said and done, I don’t really understand the theory behind the slanted Barrel port, except maybe to relieve the unnatural 90-degree turn the released air makes (and so make the air path a little smoother by a few degrees?
Endo, thanks for the input on my mystery barrel. I agree, and suspected it might be the Czech-made barrel but not the CZub barrel, or the Taiwanese-“German” barrel.
Darryl
Darryl, it is very similar to mine – I would say they are the same barrel – the “Cz made” barrel based on what Petr said (but not the CZUB factory barrel).
I smoothed out the TP opening so it will not cut the o-ring in the breech.
Dman, have you tried to slant the TP hole to see if it improves the air dynamic and thus speed?
I drilled mine with a 3/16 endmill (.187) .140 from the end… then elongated it .040 toward muzzle.
I drill the TP prior to cutting my unless. Then I indicate it back in on the lathe and cut a 1.5 – 2 deg. Unless
After that I polish it with a crafted bit then go in with JB bore paste.
No issues with pellet tipping .
This was a huge gain..
Haven’t messed with it in sometime. … but I’ve got a.few things I wanna try.
Scott… what gains did you notice from your valve mods??
except for eliminating a few burrs on the inside of the barrel port (the inside of the barrel), the barrel looks to be in pretty good shape. Whoever made the barrel did a good job on the crown, as I’d mentioned before. The barrel seems to be a shooter. I may try some 16-grain AA pellets I have laying around.
Sorry but my little digital camera doesn’t do closeups well.
Darryl
Darryl, the air leak might disappear after a few shots. If not, give it a little grease on the wall and push the barrel into the breech a bit harder and “lock” the barrel with the set screw before tightening the barrel clamp. This might help. If not, send it to Dman…
Regards,
Endo
Thanks Endo,
Darryl, the air leak might disappear after a few shots. If not, give it a little grease on the wall and push the barrel into the breech a bit harder and “lock” the barrel with the set screw before tightening the barrel clamp. This might help. If not, send it to Dman…
Regards,
Endo
Ok … 4.4 to 4.5 mm or @ .173 – .177″ LOL, :biggrinn:
It is 4.45mm (or 4.50mm) x 5.0mm elliptical TP hole. Because the hole is slanted, the exact dimension is difficult to measure.
Darryl, the air leak might disappear after a few shots. If not, give it a little grease on the wall and push the barrel into the breech a bit harder and “lock” the barrel with the set screw before tightening the barrel clamp. This might help. If not, send it to Dman…
Regards,
Endo
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I’m just gob-smacked by how well your gun has performed. That’s tuning!
Darryl