What kinds of flow mods will provide a performance (either power or efficiency) in .177? There seems to be a consensus that stock port sizes are already at the maximum for .177 and any enlargement of ports, etc will actually cause a LOSS in performance. Thoughts?
I am thinking of completely removing the valve poppet return spring and allowing the air pressure itself to close the valve. The idea is that there will be less work for the hammer spring to do, thereby allowing me to decrease preload and further ease cocking effort. I realize that filling the gun from empty may prove problematic, but the logic seems sound. Thoughts on this? Does the spring even matter? I would think 1500 psi of air is already pushing much harder on the poppet than the spring ever would. What about lighter springs? That .045” spring is stiff!
Patrick, here's a worksheet I use when I'm blueprinting a PCP's porting and planning what types of flow modifications to make.I take my calipers and gauge pins to the various parts and load in the IDs and ODs into the "Before" table. Then I put in my caliber at the top and look down the last column to see where the restrictions are. Take note it gives the area as a percentage of the caliber, so for example if you wanted to follow the "75% of bore diameter" rule of thumb for a pellet shooter, the corresponding area you want to see in that column would be 56% because of the squaring term.From that, it's easy to identify which parts need to be modified, but perhaps just as importantly, which ones don't. I take the parts in my hand and look at how I can modify each one (and by how much) to alleviate the restriction, and I plug those numbers into the "After" table. It makes it easy to play with the numbers and see the result, particularly for flow paths that involve two parts. A good example is your question about reducing the poppet OD. In some cases it's necessary to also bore out the ID of the valve to get enough flow. This little spreadsheet makes it easy to see the net result of doing both mods.
Do you have a chart for any other calibers?
I know that you can order special regulators for the Ninja bottles, I get up to 900fps with 1800psi in .22 with a stock (pinned valve) on a 2240
There's not much point in going over the equivalent of the bore diameter. The generally accepted guideline is to use about 75% of bore diameter for pellet shooters and full bore porting for bullet shooters or super heavy pellets. To my way of thinking, a 10gr in .177 is heavy and a 16gr is super heavy. So the 13.4gr you are looking at using is around the tipping point. As a practical matter, you don't really have to worry about negatively affecting efficiency by having "too much porting".
I think you have that exactly right. You can get away with not having the poppet spring in a regulated system. In an unregulated rifle, doing so will tend to produce a shorter usable shot string. The downside, as you stated, is getting it filled from zero. There's a good chance you wouldn't be able to do it with a hand pump but with a tank you should be fine.
If you try and reduce the diameter of that Disco poppet, you will end up with three pieces....
You can, however, get the poppet from an MRod, and bush the stem hole in the Disco valve down to 1/8" (is it currently 5/32").... For the bushing you can use a short piece of K&S brass hobby tubing, glued in place....
Patrick, here's a worksheet I use when I'm blueprinting a PCP's porting and planning what types of flow modifications to make....From that, it's easy to identify which parts need to be modified, but perhaps just as importantly, which ones don't.
That is awesome nervoustrigger. Do you have a chart for any other calibers?
Hmm. I do seem to remember something about too much porting causing an issue where there is too much of a pressure drop in areas between the poppet and the pellet. In my mind it was analogous (as a ridiculously extreme example) to having say, a sealed 50 gallon drum in between the poppet and the pellet. Once air is released, it enters the 50 gallon drum, where it does increase overall pressure, and the pressure does need to escape through the barrel but the change is so nominal at this point that it has far less effect on the pellet, likely just escaping between the rifling and the skirt! I know the example is crazy, but I find insane examples like this to help with my own understanding of things. Does this seem right to you? I know that if we were working with hydraulics, it would make no difference, but since air can compress ... The idea is that this is much more prevalent in .177 than in the larger calibers. I'll see if I can find some quotes somewhere... I want to be sure of what I am doing before I start getting things on my drill press.
That makes sense to me. The return spring has a lot to do with the "balanced" valve thing in an unregulated gun then? It flattens the string?
So what level of effect do you think this would achieve?
... Are those numbers arbitrary? A caliber size of .217 seems odd.
Quote from: MDStroup on August 13, 2016, 11:35:33 PMDo you have a chart for any other calibers? You can just key in your caliber at the top under "caliber for comparison".By the way, the gray cells are all calculated values. The only numbers you need to supply are for the white cells.
Love this mod You can, however, get the poppet from an MRod, and bush the stem hole in the Disco valve down to 1/8" (is it currently 5/32").... The MRod poppet is much smaller in OD (0.335"), and made of a harder material.... You get more flow around it, both between the ID of the valve body and the poppet and through the throat (because of the smaller stem).... and it is easier to open at the same air pressure.... For the bushing you can use a short piece of K&S brass hobby tubing, glued in place....you can make your hammer lighter too helps with efficiency and shot cycle
Patrick, here's a worksheet I use when I'm blueprinting a PCP's porting and planning what types of flow modifications to make.
Frankly I don't see any appreciable benefit. I've run the numbers a couple of times and the force of the air pressure holding the valve closed is so much greater than that of the valve spring, that it does not affect how hard it is to cock in a meaningful way.
5.5mm = .2165inNot so odd after all
Thanks. I will have to try that if o dont throw my maximus off a bridge first.
...because you have that on/off on the HPA bottle. Cock the strikerm fill the bottle with it to "off", turn it to on, and hit the valve all at once with 1200psi...it will seal.Reduced valve seal diameter really can increase power, more so as you've got the barrel length.
Smaller diameter poppet seal is held closed by less force, so it takes less force to open it to the same dwell...which gives hop to more air flow without excessive cocking effort. So yes, I would go with that mod first.
The poppet stem od was tricky, as I had two different diameters to deal with. I went with the larger one (the smaller one was .143) because I figured that as the valve is open, the larger diameter is largely what I see when peering down the exhaust port.
The probe had two different diameters as well. The small one was .070. I went with the large one here as well. Why is it shaped like this anyway?
It appears that I am already pretty large on my porting for .177. The MRod poppet seems like it would be overkill, seeing as how I am already at 224% there ... I guess it would help with turbulence... What about the transfer and barrel ports? Other thoughts?You once told me that getting the 16.2gr Beasts would be impossible to get to 900fps with ~1500 psi ... What about the 13.43gr monsters? Has anyone successfully run 1600psi with a 1.8k burst disc?
[regarding removing the valve spring] What about consistency or other things...?
Huh... I had forgotten that .22 airgun is not the same as .22lr! Why is this, anyway?
(OK...I kept the laminate grips and he got the black plastic girips that match the fore end.)
I think this one would be better represented as an in-between dimension. I don't know why they have the bulb on the end. I would remove it (and have done it).
Larger porting changes the picture significantly but as you stated, the barrel port needs to be a slot so as to prevent chambering issues. For example, a 0.130" wide slot that is 0.168" long equates to 74% of the bore area, and would probably allow you to reach your goal with 1400psi. A matching transfer port would need to be fashioned as well, and preferably blend the exhaust port to it.
You can, however, get the poppet from an MRod, and bush the stem hole in the Disco valve down to 1/8" (is it currently 5/32").... The MRod poppet is much smaller in OD (0.335"), and made of a harder material.... You get more flow around it, both between the ID of the valve body and the poppet and through the throat (because of the smaller stem).... and it is easier to open at the same air pressure.... For the bushing you can use a short piece of K&S brass hobby tubing, glued in place....