FX Impact Plenum Extension

It's more involved. The rear block is opened to 3/8" I believe and the valve housing has to be machined to remove one of the three legs. I'd say all those guns were done by Mr Rowe or to his spec. They all probably have 6.5mm valves and the valve rod spring moved forward as well.

I would suggest you can achieve almost as much with the MKII tuned correctly as with the plenum extension added, which as I understand it is a very inneficient use of air, but of course if you have an abundance of the older model availible why not.

I would suggest you can achieve almost as much with the MKII tuned correctly as with the plenum extension added, which as I understand it is a very inneficient use of air, but of course if you have an abundance of the older model availible why not.

Click to expand...

A larger plenum should always be more efficient. It doesn't dump the entire volume in every shot, it just provides less pressure drop as the projectile travels down the barrel.

.22 won't show a lot of improvement but as the caliber increases the benefit will be much greater.

I would suggest you can achieve almost as much with the MKII tuned correctly as with the plenum extension added, which as I understand it is a very inneficient use of air, but of course if you have an abundance of the older model availible why not.

Click to expand...

Sorry to contradict you but what you are saying is 80% wrong and a 20% right (just kidding) let me explain

Plenum in old impacts is about 20cc

Plenum in new ones mk2 is about 25 cc, that only will not help a lot, and actually most of the impacts on RMAC were mk2 still with the external plenum.

Plenum extension is 40cc

(Note cc are not exactly those, probably close, the idea is to get the volume %) 

As heavy mentioned, is not just to get the plenum, if you just install that without other mods will not work properly, in order to work you need to remove the lower of 3 bridges on the valve house so the air on the plenum will not crash against it, and drill the gauge hole. Without drilling you are restricted by the delrin and the delrin holder of the block (3mm +- hole). In order to use a "standard" plenum with a 5.2mm (+-) hole, BUT I have seen even 14mm hole on that plenum m14 thread (for the 0.35 if I recall correctly), and for that you need to make a big hole on the block. 

So, if you just install that external plenum you are right it is inefficient, since you need to make a few extra mods in order to work as it supposed.

Probably something like 8mm will be perfect for an external plenum, I will machine a few in the near future for testing.

I don't know about before, but mine is 4/5 times in the single digits.

Wow! I have so much more to learn about my FX ImpactX. It's the second airgun I bought after realizing I did not like the first: an AA TX200 MKIII because it is a Springer and I definitely prefer PCP airguns. Not into the artillery hold -- want to shoulder like a traditional firearm. And much better Max power with the FX as well as being adjustable for tuning with different pellets in a particular caliber or even switching from .25 to .30 caliber. The one thing I like better in the TX200 is the trigger is able to be tuned to a single-stage with no creep and about 2 ounces of pull. Just barely touch and fire!

@edosan - ahh yes, I know what you mean now about the 3 bridges. I have wonder if that compromises anything by removing them? 

Trying to get a mental picture of the airflow, it seems like it would be somewhat turbulent with a small hole. I want to see what people are getting for spread / ES before and after, out of pure curiosity. 

Thanks for the detailed reply Holmes  

Click to expand...

Hey buddy! no, no problems at all. Before to get into remove that bridge, like this: 



"impact geeks" lead by ER where trying several other ways (milling and make the bridges thin) and that comes with lots of problems, broken VHousing included. 

Here you can see why the milling and bridge removal is needed (closer look you see that bridge in the way of the air flow)



and here I pic I borrow from Ernest, showing an m16 hole! a BIG MF! jajaja



jaja what Holmes? Elementary? or Iron Man? jajaja

BTW how is your compressor going? 

Does Ernest also modify the pellet probe screw? as IMO the gun is dangerous without this even at 60FPE let alone over 100FPE!

Does Ernest also modify the pellet probe screw? as IMO the gun is dangerous without this even at 60FPE let alone over 100FPE!

Click to expand...

yes a LONG time ago, in 2016! first gen impacts had a problem there. (Broken screw)



https://www.youtube.com/watch?v=HVMSHdTZfnI



New ones does not have that problem. I have seen many impacts (and I own 2 myself) and none had the problem you mention in one of your posts. Still I think that 2 screws might be better and what you did is good.

If that screw get unscrew long enough to lose the probe to be an actual danger if you have the butpad down, you will not be able to cock the gun. 

After watching the video it looks like extending the large top screw into a recess in the probe would be the simplest answer for FX.

You don't need a extension. The impact already has enough power to do most pesting. Even coyotes. Imo it looks ugly having a huge thingie where the reg gauge is at. But I guess ppl prefer having that ugly thing to get the power they want.

Hey! You do not even need an impact mk2 for coyotes!

@edosan - ahh yes, I know what you mean now about the 3 bridges. I have wonder if that compromises anything by removing them? 

Trying to get a mental picture of the airflow, it seems like it would be somewhat turbulent with a small hole. I want to see what people are getting for spread / ES before and after, out of pure curiosity. 

Thanks for the detailed reply Holmes  

Click to expand...

Hey buddy! no, no problems at all. Before to get into remove that bridge, like this: 

"impact geeks" lead by ER where trying several other ways (milling and make the bridges thin) and that comes with lots of problems, broken VHousing included. 

Here you can see why the milling and bridge removal is needed (closer look you see that bridge in the way of the air flow)

and here I pic I borrow from Ernest, showing an m16 hole! a BIG MF! jajaja

jaja what Holmes? Elementary? or Iron Man? jajaja

BTW how is your compressor going?

Click to expand...

I looked at that part in the flesh and with all due respect, IMO it is madness to remove 1/3 of the support on that part.

Ya - I thought it looked weird at first but after getting it back from Ken Hicks at Southern Precision Air Weapons my MKI Impact is slinging JSB 33.9 MKII pellets at 933 FPS with a standard deviation of 3 FPS and that is after tuning it down. He had it over 75 FPE topped out and will come in handy when I swap out the liner to shoot slugs. The additional plenum space helps when slinging slugs and heavier pellets for a more consistent air pressure as the projectile moves down the barrel is how it was described to me as being the benefit of the extra plenum volume.



Here is a video of my results so far - posted from another thread... I am new to this platform, but so far I am blown away. But then again I have nothing to compare it to.

https://www.youtube.com/watch?v=TaGSR11HL0Y&t=

The external plenum looks good / fine to me...if you're after aesthetics idk why you'd purchase an impact anyhow...its more known to be feature rich in a package that is very user friendly and compact...I've seen some beautiful rifles in my day and the impact is not on that list...nor is mine when it comes to over the top aesthetics...the more you understand how pcp's work and how regulated air volume is important, the more you appreciate the 'beauty' of an external plenum that over doubles your available volume @ the regulator plenum.



Plus, if you don't like the look of the external plenum, then don't have one installed! 



-Matt