Larger plenum test on Impact X .30 700mm ... Test No Good See Edit

Jump to latest Follow Reply
I just pulled the reg gauge (for about the 100th time), and the valve housing hole is not perfectly centered on the aluminum housing hole, but it's not being blocked at all since the hole in the aluminum is quite a bit larger. The smaller valve housing hole is about 2.5mm diameter. If you were serious about increasing the regulated air chamber, it would certainly be worth matching and enlarging those holes. 

FWIW, my Impact was made around May 2017. 

Rusty
 
Upvote 0
I would certainly agree that you can't have too large of a regulated chamber, though of course there are diminishing returns as you get larger. If the regulator gauge doesn't move when you shoot, it's big enough :) 

As for transfer ports on the Impact, it's certainly less than ideal for the air to have to make that sharp 90 degree turn to flow down the barrel. We can't really change that, so all we can do is vary the TP area. I would bet that we need more TP area than the cross sectional area of the barrel, in order to overcome some of the flow restriction of the sharp 90 degree turn. If we're physically limited to an insufficient area with one TP hole, then I'd bet two will be better, and I'm not sure having too much TP area would be bad in any way. I do agree that the milled area around the brass barrel inlet is going to waste a bit of air, but I'm not sure how significant that is.

I really look forward to doing more testing on this eventually.

Rusty

Click to expand...

There is no plenum large enough except infinite, to get maximum value out of any configuration, its just how physics works, until you reach infinite there will always be pressure drop which equates to losses... same applies to air and fluid dynamics except in reverse when you increase wasted volume, until you reach 0 wasted volume, any more added is going to create losses... its a very simple concept...being that the air discharged is in supercritical state and its physical properties are in between a gas and a fluid...the valve seat is a SINGLE source of air, one exhaust...you don't want to transfer that ONE source into TWO sources (two ports) then back DOWN to 1...I can't explain it ANY simpler than that...if you can't understand how transfer plenum/port volume and waste DRAMATICALLY effects thermal efficiency, then please thoroughly read the article in regards to internal ballistics I shared...
 
Upvote 0
I value everyone's input here. In another thread Earnest Rowe told a guy that it's better to elongate the transfer port than to dill it larger. Then he said he would rather have a dual transfer port than an elongated one. What's the easiest way to add hammer weight? Wouldn't a stronger spring be better than weight? Mr Rowe said he was pushing the heavy .25s to 1025 fps.

No need to get excited. Parts can be changed back to original at any time.
Click to expand...

Forgot to mention, I also made my TP a bit bigger, 5.5x7mm. Matched probe hole size to TP. Easy job for everyone with some basic tools.

A heavier spring will make the forces on the sear higher, a higher cocking efford, and makes the hammer mover forward faster.

A heavier hammer (added hammer weight) has more inertia, thus it will move forward slower, but will be able to open the valve easier due to the heavier weight. It will keep the valve open for a bit longer time too.

What is better? I actually can't say. Light hammers have a short lock time, which is good for efficiency. I am a fan of high regulator pressures, and a short valve dwell time.

I don't know the exact velocity difference between a 600mm and 700mm barrel, but my guess is that my gun will be very close to 1025fps too with the longer barrel.

That is the good thing about the Impact, it is a very easy platform to try out new things. Main reason why I bought mine :)
 
Upvote 0
Click to expand...

Forgot to mention, I also made my TP a bit bigger, 5.5x7mm. Matched probe hole size to TP. Easy job for everyone with some basic tools.
Click to expand...

How did you enlarge the TP and what's the orientation of the 7mm?
Click to expand...

I have a milling machine, and milled it out to a size of 5.5mm wide, and 7mm long (TP size in action is 7mm in diameter) Probe likewise, but I filed it out with a 5.5mm chansaw file.

But with some patience and care, the TP can be done by some filing too, or even better, with a dremel. It is brass, so quite easy to work with.
 
Upvote 0
the ultimate limitation of the transferport size is the barrel internal diameter, no matter how big you go on TP in the end the caliber and the pellet position and barrel length that what limits the flow. the dual tp is just for preventing the pellet from falling into the hole or damage to the skirt



got no Impact but why dont you guys make the tube fatter the one which connects the reard and front blocks?

use that instead of adding those ugly outgrowths😁
 
Upvote 0

got no Impact but why dont you guys make the tube fatter the one which connects the reard and front blocks?

use that instead of adding those ugly outgrowths😁
Click to expand...

I've seen it mentioned by Ernest, but haven't seen any pictures, so I don't know if it's been done. I'd probably be afraid to try to make something like that considering the pressures involved. 

Rusty
 
Upvote 0
My new Huma high pressure regulator (145 to 190 bar) ships from the Netherlands tomorrow so as soon as it gets here I'll install it, the larger valve seat from Earnest Rowe and elongate the transfer port a bit. I'll see about a stronger hammer spring or adding hammer weight while I have it apart and then give it a try across the chronograph. The FX regulator creeps up 20 bar overnight so Huma says their regulator solves that problem. We'll see.
 
Upvote 0

got no Impact but why dont you guys make the tube fatter the one which connects the reard and front blocks?

use that instead of adding those ugly outgrowths😁
Click to expand...

I've seen it mentioned by Ernest, but haven't seen any pictures, so I don't know if it's been done. I'd probably be afraid to try to make something like that considering the pressures involved. 

Rusty
Click to expand...

Isn't that what they just did on the Impact mark 2.....?
 
Upvote 0
 

From the testing I have done,(admittedly not on an impact) duel ports offer few gains unless the Reg pressure is low, it’s only then they come int there own. To gain power you need to smooth out the air flow not just make the holes bigger. Compressed air is thick and viscous, the higher the Reg pressure, the thicker the air becomes, any acute turns or sharp edges really sap power. while I haven’t collected my impact yet, I already have plans to modify several parts that look suspect in a hope to improve performance. 

By comparison to many airguns the impact plenum is huge, the barrels are long and the Reg pressure is high, so power should not be an issue so something somewhere is holding it back, in an ideal world, For maximum power/ efficiency/ consistency, air should move seamlessly from bottle to muzzle,.

i will let you know how I get on ( or not) when mine finally arrives 

.

Bb
 
Upvote 0


From the testing I have done,(admittedly not on an impact) duel ports offer few gains unless the Reg pressure is low, it’s only then they come int there own. To gain power you need to smooth out the air flow not just make the holes bigger. Compressed air is thick and viscous, the higher the Reg pressure, the thicker the air becomes, any acute turns or sharp edges really sap power. while I haven’t collected my impact yet, I already have plans to modify several parts that look suspect in a hope to improve performance. 

By comparison to many airguns the impact plenum is huge, the barrels are long and the Reg pressure is high, so power should not be an issue so something somewhere is holding it back, in an ideal world, For maximum power/ efficiency/ consistency, air should move seamlessly from bottle to muzzle,.

i will let you know how I get on ( or not) when mine finally arrives 

.

Bb
Click to expand...


The valve (seat ID) is the bottleneck above .22 cal. The transfer port in the brass barrel inlet should be flared deep at it's entry and elongated forward where it enters the breach, with the forward edges smoothed. This tilts the port forward slightly. Then open the feed hole in the pellet probe a good bit larger than the port feeding it and knife edge the edges. You should not be able to see the edges of the pellet probe entry when looking through the barrel inlet port. Then remove the top half of the pellet probe from the feed hole forward and knife edge the cut edges.

The greatest gains will be under .30 cal and heavier projectiles will produce the highest energy.
 
Upvote 0


From the testing I have done,(admittedly not on an impact) duel ports offer few gains unless the Reg pressure is low, it’s only then they come int there own. To gain power you need to smooth out the air flow not just make the holes bigger. Compressed air is thick and viscous, the higher the Reg pressure, the thicker the air becomes, any acute turns or sharp edges really sap power. while I haven’t collected my impact yet, I already have plans to modify several parts that look suspect in a hope to improve performance. 

By comparison to many airguns the impact plenum is huge, the barrels are long and the Reg pressure is high, so power should not be an issue so something somewhere is holding it back, in an ideal world, For maximum power/ efficiency/ consistency, air should move seamlessly from bottle to muzzle,.

i will let you know how I get on ( or not) when mine finally arrives 

.

Bb
Click to expand...

I'm off topic here. But there's a lot of info. in this post that pertains to me. 

Interesting....I was forced to build a duel PT system on a gun because of size limitations. 

The two ports have a 30% larger combined volume than the port that feeds them.

Used a ball end mill to round the inside, but I still have a sharp edge at the muzzle end of the ports. 

I thought I'd probably have to address that. Clearly I better. 

After I work out the sharp edges I'll re-chrony to see if there's is any significant improvement. 
 
Upvote 0
To get maximum flow from the external plenum tube:

1. bore out gauge hole to M14X1.5 ----->75-100fps increase

2. need new plenum with M14 X 1.5 with 9mm bore hole 

3. valve housing need clear passage for the 14X1.5 bore ---see photo

4. the smallest air restriction are the transfer port on barrel and pellet probe, so dual port them see photo 45-65fps+ increase

FPS are actual testing---> no math !



is.php


is.php


is.php

 
Upvote 0
To get maximum flow from the external plenum tube:

1. bore out gauge hole to M14X1.5 ----->75-100fps increase

2. need new plenum with M14 X 1.5 with 9mm bore hole 

3. valve housing need clear passage for the 14X1.5 bore ---see photo

4. the smallest air restriction are the transfer port on barrel and pellet probe, so dual port them see photo 45-65fps+ increase

FPS are actual testing---> no math !



is.php


is.php


is.php
Click to expand...

Ernest, here's a picture of the ported and polished valve housing I did, similar to how we port engine's head intake and exhaust ports. It flows air so much better after the valve seat is opened. Top speed was 980 fps @ 174 bar with 50.15 grain JSB's. I didn't open the reg any higher.
1555356723_10956196175cb4dc3344e056.14528122_IMG_20190412_213557943~3.jpg

 
Upvote 0
Nice, that usually get me 5-10fps by porting but got 10fps more by enlarging the TP then nozzle shape porting. I,m testing a 7.15mm VS with 7.65mm rod seat with impressive results.
Click to expand...

Yes, I port-matched the block and brass transfer port as well. The pictures don't do this part's port job justice. I would like to buy your titanium valve stem and matching 7.15 mm valve seat to complete this gunsg set-up. Right now I am maxed out with the stock valve stem seal and ported 6mm valve seat opening. Please let me know... Thanks.
 
Upvote 0
You must log in or register to reply here.
Top Bottom
Back
Home
Forums
Resources
Menu