Talking about the impact here. Stock is 20cc. What is the maximum plenum volume before you do not get a climb in power anymore. I'm sure there is a limit. Example at 60cc I get 1000 fps. 65cc I get 1020 fps. Then at 70cc, 80cc, 90cc etc. I'm still getting only 1020 fps. So maximum plenum is 65cc. Anyone done any testing to see what is the maximum volume for an impact plenum?
How much is too much plenum?
- Thread starter 2fast2furious
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The common / frequently used goal is @ 1cc in volume per ft/lb of output.
less volume requires a slightly higher set point to equal a larger plenums power. More plenum above 1cc per ft/lb buy you a bit more power potential should you increase caliber, weight or wish to use ever higher pressure.
There are a lot of guns operating under the 1cc per that shoot just fine. Tho as you get a larger plenum the pressure drop within plenum every shot is less and in properly tuned guns equals a bit tighter ES value.
JMO ... nuttin more or less
less volume requires a slightly higher set point to equal a larger plenums power. More plenum above 1cc per ft/lb buy you a bit more power potential should you increase caliber, weight or wish to use ever higher pressure.
There are a lot of guns operating under the 1cc per that shoot just fine. Tho as you get a larger plenum the pressure drop within plenum every shot is less and in properly tuned guns equals a bit tighter ES value.
JMO ... nuttin more or less
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Theres probably a maximum amount of plenum the valve can dump between valve opening and projectile leaving barrel. Would probably involve some math 
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Theres probably a maximum amount of plenum the valve can dump between valve opening and projectile leaving barrel. Would probably involve some math
Or by testing different size plenum till you reach a maximum fps/fpe. If I have the tools to make different size plenum I would test it.
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There should definitely be a max. Even if you could dump all of that air, there’s only so much barrel. So, basically, air would still be dumping into an empty barrel because the projectile would have already exited the barrel. So, basically it will be a waste, unless you lengthen the barrel.
That’s the theory / explanation I have heard before. Makes kinda sense to me though.
That’s the theory / explanation I have heard before. Makes kinda sense to me though.
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I have no experience with the impact but have tuned a few regulated guns. I think a plenum volume should be at least a little under what is needed for maximum FPE.
If the plenum is oversized by a significant amount, hysteresis in the regulator may cause it to be static (stuck) for several shots until the plenum pressure falls enough to activate it. I want every shot to dump enough of the plenum volume to activate the regulator.
With a small enough plenum, the regulator will activate every shot, and hopefully keep the plenum pressure more consistent, shot to shot.
An oversized plenum can certainly work, but, depending on the regulator, may not be an optimal tune. Oversized will give you maximum FPE, if that's what you want, but it may not give best consistency.
If the plenum is oversized by a significant amount, hysteresis in the regulator may cause it to be static (stuck) for several shots until the plenum pressure falls enough to activate it. I want every shot to dump enough of the plenum volume to activate the regulator.
With a small enough plenum, the regulator will activate every shot, and hopefully keep the plenum pressure more consistent, shot to shot.
An oversized plenum can certainly work, but, depending on the regulator, may not be an optimal tune. Oversized will give you maximum FPE, if that's what you want, but it may not give best consistency.
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Scott<
A Regulators willingness and accuracy of reset pressure is IMO an entirely different rabbit hole of discussion. You make a valid point I will agree and should the OP wish to go down THAT HOLE ! we would be more than happy to help in that conversation too.
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My understanding is that you cannot have a plenum too large. The only determining factor for that would be the actual mass. And resulting encumberance/obstruction in regards to the external dimension of the gun. Who wants a basketball sized plenum on their gun? Not this guy, lol.
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P1*V1 = P2*V2
Solve this equation using the data of your gun and you know the answer. Everything in the universe is made of math. To answer all the question about of the PCP airgun is necessary apply the physics laws.
Solve this equation using the data of your gun and you know the answer. Everything in the universe is made of math. To answer all the question about of the PCP airgun is necessary apply the physics laws.
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I agree but that tells you what's required for max performance. You can have too little but you can't have too much. In other words performance will not be reduced if you have more plenum than is required for maximum performance. Anything over will just add to your shot count.
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