Tuning FX Impact Mk2 PP valve seat porting

[Seeker]

Hi,

The original valve seat hole is about 6.35mm. I think about enlarging it 7mm. It requires me to use a bigger valve poppet as well.

Do you have any data if it can help with FPS gain in .30 with a 500mm barrel?

When I go to big I will have the problems with valve opening - more hammer weight needed. There is also not much room for the air around the poppet so if I go too big I may have an opposite effect.

This is what I found: https://www.airgunnation.com/threads/impact-pp-valve-housing-2-0.654925/

But there is no specific info about gains.

Thanks.

 

[Airgun-hobbyist]

Hi,

The original valve seat hole is about 6.35mm. I think about enlarging it 7mm. It requires me to use a bigger valve poppet as well.

Do you have any data if it can help with FPS gain in .30 with a 500mm barrel?

When I go to big I will have the problems with valve opening - more hammer weight needed. There is also not much room for the air around the poppet so if I go too big I may have an opposite effect.

This is what I found: https://www.airgunnation.com/threads/impact-pp-valve-housing-2-0.654925/

But there is no specific info about gains.

Thanks.

Your gains with a short barrel are going to be less, and likely waisting air. The longer the barrel the more the benefits of opening up the poppet valve seat and smoothing airflow is shown.

Here's a thread on the port job I did to the Gen 1 Impact's internals. Search out the other posts that I made on porting and aligning the Impact's transfer ports to get other pictures and the final porting gains. The poppet valve's surface area was a lot smaller from the factory back then. I think my poppet valve seat is ported to around 6.35mm--6.5mm now, using original poppet and rod. Everything is different with the parts now so opening it up to 7mm may easily be done.

FX Impact valve housing modifacations

I gave the transfer ports on the valve housing, block, barrel, and pellet probe a port job worthy of a top fuel dragster engine! That took a bit of finess with a Dremel tool, and a lot of measuring and fitting to make all three parts and their ports match and flow well. The pictures don't do...

www.airgunnation.com

 

[qball]

your best bet for any significant power gain especially with short barrel is the power block upgrade kit for MK1&2. Significant power gain if you push the gun to the limit.

 

[Seeker]

Any prediction how many FPS I can gain? Now I am at 950FPS with FX Hybrids .30 and 500mm barrel. 170 bar on a reg.

 

[Bigragu]

Any prediction how many FPS I can gain? Now I am at 950FPS with FX Hybrids .30 and 500mm barrel. 170 bar on a reg.

Man that gun must jolt upon firing. Hard on the internals for sure.
966-970 was the best I could get with a 30 shooting the hybrids, 600mm barrel, and at that speed it was shooting the hybrids with pellet like hunting accuracy, and got 36-38 shots off of a 480cc bottle(regulated shots, I might add) With a 700mm I was able to get 988 FPS, same shot count and accuracy.

I know shot count doesn’t matter to some, but on these guns the owners wanted a good combo of power, shot count, and accuracy

 

[2L8]

Any prediction how many FPS I can gain? Now I am at 950FPS with FX Hybrids .30 and 500mm barrel. 170 bar on a reg.

Seeker, am I understanding you correctly, that your question is about power only?

Patrick

 

[Seeker]

No, accuracy is very important for me as well. 950FPS is max what I can get but I shoot Hybrids at 920FPS from a 500mm barrel and this is what I get at 50 meters:

My Impact Mk2 is customized. PEEK valve poppet, ported pellet probe, polished channels and everything aligned perfectly using a bore scope. I wonder if I can squeeze a couple more FPS without killing accuracy if I enlarge the valve seat to 7mm.

 

[Airgunmann]

I think the only difference in the power block is larger transfer porting which can be done to the original block you would just need to drill and tap out to larger set screw in the top of the block going larger with the valve you should be able to gain a few fps on top of what you have already

 

[Seeker]

My valve housing hole is aligned perfectly with the hole in the block. I can't see any potential gains there.

 

[qball]

Hard to say at that power level with such short barrel, my GUESS is about 20fps, that speed is close to the physical limitation of the 500mm barrel on an airgun but the high reg setting really helps. Like I said the kit has everything you need even with warranty on top, best option IMHO.


My MK2 went from shooting .22 38 grain slug @900 to about 950 after and could go higher, my reg is at 160ish with 700mm barrel. Higher the reg pressure the bigger the difference you will see from removing the restrictions. You obviously know what you doing when it comes to tuning, plus hybrids are pretty light so good chance on getting descent speed bump. Good luck!

The porting can only go so far before hitting the restriction in the block, you need the full PowerBlock kit that has bigger poppet and passage and 720 plenum. Add a regulator rebuild kit with brass piston plus tungsten hammer your MK2 is meaner than a new stock M3 with all new orings for the internals/full reseal.

 

[Airgunmann]

If your going 7 mm in the valve I'd open up every thing to the transfer port on the barrel as much as possible because the daul transfer port has a big opening in it

 

[Airgunmann]

Does some one know the size of the set screw and porting in the power block I did the 720 pp in my mk2 but not the power block I'd like to open the passages in my block up to power block size without buying the power block I thought it was coming in the kit but I was wrong

 

[Seeker]

Hard to say at that power level with such short barrel, my GUESS is about 20fps, that speed is close to the physical limitation of the 500mm barrel on an airgun but the high reg setting really helps. Like I said the kit has everything you need even with warranty on top, best option IMHO.


My MK2 went from shooting .22 38 grain slug @900 to about 950 after and could go higher, my reg is at 160ish with 700mm barrel. Higher the reg pressure the bigger the difference you will see from removing the restrictions. You obviously know what you doing when it comes to tuning, plus hybrids are pretty light so good chance on getting descent speed bump. Good luck!

The porting can only go so far before hitting the restriction in the block, you need the full PowerBlock kit that has bigger poppet and passage and 720 plenum. Add a regulator rebuild kit with brass piston plus tungsten hammer your MK2 is meaner than a new stock M3 with all new orings for the internals/full reseal.
View attachment 290675

Tungsten hammer seems to be an overkill for such a short barrel. Even with 170 bars on reg.

 

[qball]

Tungsten hammer seems to be an overkill for such a short barrel. Even with 170 bars on reg.

Yes, definitely something to be watching out for and possible problem with valve open too long. To open the valve at 170 bars you will need something more than stock hammer and spring. The FX tungsten hammer is 15g and could be too much while stock hammer weight is 7 grams and is way too light, check out Huma’s brass hammer weights in 10-13g range. However as long as you have the stock valve return spring in stead of the weak slug kit vale return spring the tungsten hammer can be controlled fairly well.

There is someone on eBay (possible on agn too) sells custom tungsten hammer weight and you can choose between 11-15 gram, mine is 14g.

 

[rcs9250]

Not to hijack this thread but something I learned some years ago with gas flow through orifices. It might apply here but don’t know as I have not torn any air guns apart yet, someday though.
Anyway, and I realize 6.35 or 7.0mm is a pretty good size hole. One thing that has an effect on airflow or any gas is the microfinish on the walls of an orifice. A drill will leave a helical finish, a reamer can leave a similar but smoother finish and honing or polishing leaves a better finish.
Where I learned it was with a GE burner that was used for making light bulbs to melt glass after pulling a vacuum on the bulb. We normally drilled the gas holes but in doing some research I found a vendor that did a process called micro edm. The micro EDM burned the hole through the part as compared to a rotating tool. The customer always did a flow test when we shipped in parts. The engineer called me asked how we machined this batch of parts. I explained and asked why he enquired. He said the flow rate was much higher in the EDM’d parts.
The prior parts had helical lines in the walls of the orifice which created a vortex of sorts which also created drag. The EDM’d parts gas flow was laminar and flowed with much less drag/restriction.
You might look at the finish in your part before you enlarge it to see if it’s a nice smooth finish or has helical lines. One thing wedon’t have access to is the drawing for the part and any spec for a microfinish.

 

[bigHUN]

This what I did back in Dec.2020, sorry the pictures were made for my own archive, today for a presentation I would definitely do them better.
This what I did (original PP). I didn't wanted to alter the original parts so I ordered new parts everything to have a spare.
The grub screw at the bottom of the RearBlock is M8, that drilled hole before tapping is 6.8-70 mm.
I toke a cylindrical carbide, I guess it was close to 8mm OD.
On my MiniMill I converted a 6.8 mm hole into a 8x9 mm slot (in the RearBlock).
But ones I had the parts in my hand, I re-drilled the ValveHouse hole as well from 6.5mm to 7.3mm ID, also mirror polished the cone (you can see the shine in the picture). Also recut the transfer hole into the same slut as in the RearBlock.
A friend of my cut a peek poppet on a lathe for me. First I had it OD 9.1mm but that restricted the airflow, and I re-cut that poppet to 8.3mm and now is working perfect.
Also, I replaced the delrin puck with a peek on the Hammer nose that hits the C1.
With these changes I have unrestricted the air path, the power increase is enormous:
.25x700 Superior Heavy, original PP, Heavy HammerSpring140 bars on the Reg propels the 44gr ZAN with 1020 fps, and still there is about 2mm travel on the HammerSpring slider. I never went into investigating how much really max power I can get.

 

[Airgunmann]

Seeker I think if you open everything up to 7 mm and add a hammer weight maybe bump the reg up to 180 bar to get a short burst of hpa and use the valve control you could see a significant gain in fps

 

[Seeker]

Yes, definitely something to be watching out for and possible problem with valve open too long. To open the valve at 170 bars you will need something more than stock hammer and spring. The FX tungsten hammer is 15g and could be too much while stock hammer weight is 7 grams and is way too light, check out Huma’s brass hammer weights in 10-13g range. However as long as you have the stock valve return spring in stead of the weak slug kit vale return spring the tungsten hammer can be controlled fairly well.

There is someone on eBay (possible on agn too) sells custom tungsten hammer weight and you can choose between 11-15 gram, mine is 14g.

Yes, I use 19.5g hammer and 7.5g hammer weight.

This what I did back in Dec.2020, sorry the pictures were made for my own archive, today for a presentation I would definitely do them better.
This what I did (original PP). I didn't wanted to alter the original parts so I ordered new parts everything to have a spare.
The grub screw at the bottom of the RearBlock is M8, that drilled hole before tapping is 6.8-70 mm.
I toke a cylindrical carbide, I guess it was close to 8mm OD.
On my MiniMill I converted a 6.8 mm hole into a 8x9 mm slot (in the RearBlock).
But ones I had the parts in my hand, I re-drilled the ValveHouse hole as well from 6.5mm to 7.3mm ID, also mirror polished the cone (you can see the shine in the picture). Also recut the transfer hole into the same slut as in the RearBlock.
A friend of my cut a peek poppet on a lathe for me. First I had it OD 9.1mm but that restricted the airflow, and I re-cut that poppet to 8.3mm and now is working perfect.
Also, I replaced the delrin puck with a peek on the Hammer nose that hits the C1.
With these changes I have unrestricted the air path, the power increase is enormous:
.25x700 Superior Heavy, original PP, Heavy HammerSpring140 bars on the Reg propels the 44gr ZAN with 1020 fps, and still there is about 2mm travel on the HammerSpring slider. I never went into investigating how much really max power I can get.

View attachment 290765View attachment 290767View attachment 290768View attachment 290769

What was your valve seat hole? The original one is 6.35mm.

 

[bigHUN]

What was your valve seat hole? The original one is 6.35mm.

6.4-6.5 or close to that cannot remember precisely. The machine shops here in Canada all using the stupid fraction sizes...that precision in my eyes in not more then a go-nogo.
I have bored it out to 7.3 on a lathe.
Also do a laping + mirror polish on the cone. I did it by hand.

 

[Seeker]

Ok, and 7.3mm hole did not decrease your v0 because of the limited space around the valve poppet. Good to know.