Tuning FX Impact X with Power Plenum tune for 25 cal 34gr JSB

[frank320]

I installed the Power Plenum kit on my FX Impact X 25 cal. With reg set at 115bar or so, I am getting about 895fps shooting 34gr JSB.

This is all good, except when I go play with the valve knob settings, I find the included valve spring way stiff. If I turn the valve knob all the way into the 4th/3rd line or less, I find the hammer hitting with significant resistance, making the hammer hit the valve and return to close hard. Sounds painful and needlessly stressing the system 

I am now opening the valve WIDE open, way beyond the 4th line, almost at the 6th line if they had the markings on. This seems to let the hammer hit and let the valve return to close softer and smoother, making the Impact quieter. I have read that some have resorted to cutting the valve spring? 

It's like choosing between:

1) Letting the hammer hit harder and close harder for more efficient air usage, but stress the components, OR

2) Letting the hammer hit softer and return to close softer, wasting a little air in the process, but allowing a smoother less stress system

I guess I prefer option 2. Anyone else experience this?

 

[Redick]

Sounds like too much HS and not enough regulator pressure 

 

[frank320]

Sounds like too much HS and not enough regulator pressure

Well, that was that I thought initially, but if I played with the power wheel setting, I get this:

at setting Max - avg 895fps

at setting 5 - avg 870fps

at setting 4 - avg 840fps

at setting 3 - avg 810fps

at setting 2 - avg 790fps

at setting 1 - avg 765fps

at setting Min - avg 740fps

Looks to me like the HS settings are just fine.

 

[Jayman07770]

Did you measure the C1 hammer seat to the block. It should be 6mm -6.5mm. I installed PP kits on both my impacts using that recommend measurement and it works perfectly. 

 

[frank320]

Did you measure the C1 hammer seat to the block. It should be 6mm -6.5mm. I installed PP kits on both my impacts using that recommend measurement and it works perfectly.

I did measure it during the installation and it was slightly more than 6mm. To be fair, I am nitpicking here. My original stock Impact X was shooting 25 cal JSB 34gr at 895fps (SD of 4-5fps) with the reg at around 155bar. With the Power Plenum, it is now shooting the same 34gr at 895fps(SD of 3-4fps) with a reg pressure of just 115bar.

I am perfectly happy with how it shoots with the Power Plenum upgrade. I was just "fine tuning" with the valve knob and noticed the hammer strike, valve opening and valve closing sounded different(as compared to the older Impact X system) as the valve knob/spring was turned in and the valve spring compressed. It just felt like everything sounded much more "harmonious" if I had the valve wide open rather than turning it in.

 

[Mrshosted]

-How's your standard deviation? High like 8-10FPS

 

[stoti]

When you installed the power plenum parts and put the small rubber ball in there, did you also leave the little rubber ball inside the valve knob? That will add like 3-4mm and cause your problem. Take the valve adjuster off and look inside for a rubber ball smashed in there. Take it out with tweezers or a metal pick or something and your fps will go up considerably. That would be my guess. Easily overlooked.

Stoti

 

[frank320]

When you installed the power plenum parts and put the small rubber ball in there, did you also leave the little rubber ball inside the valve knob? That will add like 3-4mm and cause your problem. Take the valve adjuster off and look inside for a rubber ball smashed in there. Take it out with tweezers or a metal pick or something and your fps will go up considerably. That would be my guess. Easily overlooked.

Stoti

Pretty sure I installed the power plenum kit correctly. I do think the Power Plenum kit's valve return spring that was included with the kit is too stiff, and it looks like FX feels the same way. Seems like the latest FX Slug Power Kit includes a lighter valve return spring for more power and higher hammer loads.

https://utahairguns.com/fx-impact-slug-power-kit/

"Working in harmony with this modification is a lighter valve return spring. This lighter spring allows the valve to stay open slightly longer which allows more air through to propel heavier projectiles like airgun slugs."

I just ordered the FX Slug power kit from Utah Airguns. Sounds like a good idea and design. Should have ordered it when I ordered the FX Power Plenum kit... would have saved me installation time had I installed both power kits all in one go.

 

[frank320]

Quick update. I got the Impact Slug Power kit from Utah Airguns and installed them in my FX Impact X with Power Plenum. I installed everything from the Slug Power kit: pellet pin probe, hammer spacer/weights and also the lighter valve return spring. Here's my before and after results(all using 25 cal 34gr JSB):

FX Impact X original with no mods: Reg at 150 bar, Power wheel at Max 890fps, at Min 650fps

FX Impact X with Power Plenum upgrade: Reg at 110bar, Power wheel at Max 885fps, at Min 740fps

FX Impact X with Power Plenum and Slug Power kit upgrade: Reg at 110bar, Power wheel at Max 905fps, at Min 750fps

The latest slug power kit's lighter valve return spring allows finer adjustments. The power plenum kit's valve return spring is too stiff, but works well if used together with the slug kit's additional hammer spacer/weights for a very balanced and adjustable impact.

In summary, I like the upgrades, but I feel that the Power Plenum Upgrade kit should have included parts from the Slug Power Kit(hammer spacer/weights, lighter valve return spring). Both kits needs parts from the other kit to create an adjustable and balanced Impact. 

The adjustable pellet pin probe is a great idea, but it is not ideal when used with pellets. Every now and then, I would get a bad chambering that would result in a rough loading that then results in a flyer - about 1 in 20. That is obvious when you compare how a stock FX Impact pellet probe loads the pellet pushing on the skirts compared to a pin probe.

 

[jfgdds]

Frank320 I found your posts very helpful. I installed the 720 power plenum on my .25 cal impact x with 600 mm superior heavy liner and carbon sleeve. It has a huma dual transfer port. I also thought there was an issue with the power plenum spring. Per your suggestion I installed all the slug kit parts, including adjustable pin probe (I have not had any issues with this probe and pellets what so ever), except the lighter spring and rubber ball. I used the stiffer spring on the power plenum kit as well as the valve adjustment knob that came with it. This set up works very, very well. I set the gun to shoot jsb heavies mark2 at 915 fps.. The reg is set at 130 bar and power wheel on max. With power wheel on 5 I shoot H&N baracudas at 955 fps. They are actually shooting better than the jsb's. I could hit the ball on the end of a sewing pin 2 out of 3 shots at 33 yards. Never been able to get that performance out of the baracudas before. With this set up 90 barr of air will get me 48 shots. Once again, thanks for you input on this thread.