Beginner's questions on PCP tuning
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Beginner's questions on PCP tuning
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Topic: Beginner's questions on PCP tuning (Read 1862 times))
toine
Sharp Shooter
Posts: 776
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Real Name: Tony
Beginner's questions on PCP tuning
«
on:
January 21, 2014, 12:39:30 AM »
First, thanks to Rsterne for all the informative posts. They've helped me start to get a grasp of this whole PCP tuning concept. After hisrecent post in the Flying Dragon PCP thread about 'Correctly' tuning a PCP, I had a couple questions. More to the truth, I think I had my 'ah-ha' moment where everything clicked, but I wanted to run it past you to see if I was right.
I'll use my B50 as an example. In general they are set for high power shots. Features: Heavy hammer, heavy spring, designed for a full 3000psi-ish initial fill. On mine, with no detuning, I get a steep falloff shot to shot.
With no swap outs, I can adjust the hammer strike somewhat via the built in adjustable striker.
Now onto where I think I'm finally 'getting it' and my 'ah-ha' moment.
guess #1:
At factory settings, the hammer strike adjustment will only really on its own adjust power, and at that only to a certain extent. I'm still looking at a similar PSI fill requirement as I'm still using a 'heavy' spring to toss around a 'heavy' hammer. Lowering the PSI would probably waste air as that heavy hammer strike will just keep the valve open longer than needed.
guess #2:
Assuming no other changes, if I use a 'lighter' hammer and hammer spring, I can in essence tune down the gun to work in a similar fashion but at lower fill pressure.
guess #3:
At lower fill pressure, I'mm be looking at lower power, since there is less potential air to the gun. If I want to change this, I'd have to open up the transfer port, and possible put a lighter spring in the valve assembly itself. On other guns, such as the QB78 series, I can modify the valve in order to allow more air in as well.
guess #4:
Assuming two Identical rifles are both tuned for the same FPE, with one running at 3000psi and the other at 1500psi, the wear on the valve/valve stem will typically be greater on the 3000psi gun.
Finally, one question:
#5: In tuning to a lower PSI fill, how important is it to lighten the strength of the valve spring itself?
Thanks in advance for any guidance or advice you can share.
«
Last Edit: January 21, 2014, 12:14:10 PM by toine
»
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Re: Beginner's questions on PCP tuning
«
Reply #1 on:
January 21, 2014, 02:10:40 AM »
#1 - yes, if you have too heavy a hammer strike for the pressure, you are wasting air, whether the gun is regulated, or an unregulated PCP running on the low pressure end of the curve....
#2 - correct, any method of reducing the hammer strike, a lighter hammer, less hammer travel, and/or a lighter spring or less preload will reduce the usable pressure range....
#3 - with no other changes, once you are on the downside of the bell-curve, lower pressure - lower FPE.... If you tune a gun for he best bell-curves and then retune it for a lower pressure, again with the best bell-curve at the new, lower pressure, it will generally produce less FPE.... To regain the power, particularly at lower pressures, you need larger ports.... However, larger ports tend to like a hot cam in a racing engine.... more power but a narrower power band.... ie "peakier" and a shorter shot string....
#3b - valve spring do the opposite of hammer springs, a weaker spring makes the hammer think the pressure went down, so it opens the valve further.... However, go too light and you may increase the chance of air-wasting hammer bounce.... but don't ask me why....
#4 - I don't think "wear" is a significant factor, but the load on the seat material is greater at high pressure, so a harder poppet / seat may be needed at high pressures, and particularly with larger valve throats.... It's a matter of the pure load on the seat, which can approach hundreds of pounds....
#5? - I seldom alter the valve spring....
Bob
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Beginner's questions on PCP tuning