Piston Porting : What is it? How-to-do it

[Almighty]

I have searched through the forums and am quite surprised to find nothing on the subject of ported pistons, considering the number of posts and amount of information accumulated over the time this place has existed. I assume there are many who are actually familiar with ported pistons, mostly as a feature of many upgrade piston heads.. but don't know how it really works, what it really contributes, and that it's possible to incorporate that feature into the stock plastic piston head.

 

Here's a short piece on what piston porting is all about.

 

 

The diagrams above show the working difference between an unported piston piston and a ported one. With a stock piston, the cylinder fills up with air only thru one opening - the air nozzle. Because more often than not, there would be a BB in front of the nozzle, air passage is effectively restricted (to a degree) so much so that the cylinder may not have fully equalized (filled with air) when the piston starts moving forward (in full-auto cycle). A ported piston has holes which allow air to be drawn from the back of the piston, effectively increasing the number of intake passages. During the pull-back or draw phase, the piston o-ring moves forward against the front plate, thereby exposing/opening the holes - air rushes forward. As the piston moves forward, the o-ring slides backward, seals against the backplate-cylinder gap and prevents air from leaking backward. Its an easy assumption that the cylinder equalizes faster and therefore has more air to compress. Expect a little more power.

 

A stock unported piston drawing air thru a restricted opening will produce partial vacuum in the cylinder - the gears and motor will experience some drag, or a heavy draw. If the air nozzle was completely blocked, the motor will definitely strain, possibly stall, and not be able to cock the piston at all - the vacuum will not allow it. A ported piston, however, can still allow air in from the back and eliminate the vacuum effect totally. The piston draw will consequently be much lighter. Expect the ROF to improve.

 

 

In order to modify the stock piston, one must first separate the piston head from the piston body. Whereas it may be possible to simply twist the head off and unscrew it, there is no assurance that the head can be screwed back on and tightened sufficiently. The idea of the head unscrewing itself off while the gun is in operation is not exactly entertaining. The best way to prevent that is to carve out the center of the front (face) plate to expose the mounting screw so one can use a (phillips) screwdriver to mount or dismount the head.

 

 

This last picture is pretty much self-explanatory. It shows how the stock Marui piston assembly is put together and a couple of ways to put holes thru the front plate. There may be as few as 2 holes, and even more than 8. Don't over do it tho' as it may possibly affect the integrity of the faceplate. Personally.. I usually put in only 4 holes (I'm lazy). Make sure all the hole edges are clean and free of burrs, especially on the o-ring side (uneven surface may keep the o-ring from seating/sealing properly).

 

I hope you guys would find this little tip useful, and save you a few precious bucks or pounds you can spend on something else.

[Verymanynames]

I love these cheap garage mods. Have you done it, does it work?

[Almighty]

I love these cheap garage mods. Have you done it, does it work?

<{POST_SNAPBACK}>

The practice of porting stock piston heads has been around these parts for some 10 years, and I do it as a matter of course whenever I open a gearbox and find a fully stock piston. Anyone (here) who can open a gearbox almost always does the same thing, so much so that a ported stock piston head has become indication of a gun/gearbox worked on by someone with some degree of knowledge or experience. The modification really works. The sheer number of our local players who buy aluminum, polycarbonate, or even Deepfire piston bodies yet retain the original, but ported, stock piston heads should be enough proof it does.

[Sale]

I'm even lazier than you drilling a couple holes - I just buy a ported piston head.

 

A stock piston head with an upgraded nozzle (no + shaped opening to let air pass between the BB and nozzle) will work without completely stalling, but it's not recommended. Like you described, there will be more strain on the piston, gears and motor.

 

-Sale

[Almighty]

I'm even lazier than you drilling a couple holes - I just buy a ported piston head.

<{POST_SNAPBACK}>

We come from a poor 3rd world country - buying is not always an option. In any case, we started doing this modification during those times when aftermarket parts were but pictures on a catalog for most of us. The practice has endured for reasons of practicality, usability and hobbyist pride. Like I said, the money saved can be used to buy some other part which cannot be handmade, jury-rigged or fabricated with most ordinary shop tools.

[Verymanynames]

I agree, doing a mod to your gun with your own shop has a lot of pride in it. You feel more like a gun smith than a monkey who can swap parts Besides when someone asks what upgrades your gun has you can rattle off scary techno jargon like in the movies.

[Hissing_Sid]

Alternatively, if you drill a hole in the wrong place, you can f**k up a perfectly good gun.

 

So long as you're using a stock nozzle you'll never have to think of this again. It's only with some designs of nozzle that this becomes a problem.

 

In the right situation this will solve a problem but for 99% of the guns around it will make no difference at all.

[Almighty]

Alternatively, if you drill a hole in the wrong place, you can f**k up a perfectly good gun.

<{POST_SNAPBACK}>

I can't see how drilling a hole in the wrong place on the piston head will mess up the whole gun. While doing it wrong can certainly put to waste a stock piston head (which many here don't think twice throwing away anyway). The damage limits itself to only that far. Only those who cannot understand the given instructions and diagrams are bound to make such a fumbling error as drill in the wrong place.. and I don't think they'd attempt it in the first place.

 

So long as you're using a stock nozzle you'll never have to think of this again. It's only with some designs of nozzle that this becomes a problem.

<{POST_SNAPBACK}>

The restricted air passage at the nozzle isn't really a big problem, if a problem at all. The different offered designs only show that designers realize that the air intake could be improved further. But there's only so much redesign improvement possible for 1 small intake hole, hence the development of the ported piston head - more intake holes. The "completely blocked nozzle" was only an illustrative example how a ported piston can still be drawn back, with ease, virtually completely oblivious of the closed off air intake up front.

 

In the right situation this will solve a problem but for 99% of the guns around it will make no difference at all.

<{POST_SNAPBACK}>

If the design concept made no difference, then why are 99% of aftermarket piston heads ported?

[lacroixpamplemousse]

newb question:

 

Does the mounting block move forward to allow space between the O-ring, back and frount plate?

Is the bearing like diamond actually the o-ring?

(Im referring to your first diagram, Almighty.)

[Tommygunn]

Nice mod.

I would say, however, that the piston ring and piston head porting have nothing to do with allowing air ingress into the cylinder, which is achieved purely through the barrel/nozzle or in combination with a cylinder port.

You can see this in the true fit of the o-ring in the piston head where there is no back and forth movement, as shown in your lower diagrams.

In my opinion, piston head porting purely allows compressed air, from the forward stroke of the piston, to be directed in and against the piston o-ring making a tight and efficient seal against the cylinder wall.

Still, a good mod to save a few bob.

[Tommygunn]

Neoific,

The mounting block butts up against the inside face of the piston wall, the gap is there for clarity I suppose. All plates etc lie flat against each other.

The o-ring is round in its cross-section and it looks like a diamond because computers can't do perfect circles because of pixilation.

[Verymanynames]

Newb question, is that mounting block always there or do you have to add it?

[Tommygunn]

It's always there in stock Marui type pistons. It acts as the 'nut' for the piston head screw and also as a fixing block for the piston spring.

[Almighty]

Nice mod.

I would say, however, that the piston ring and piston head porting have nothing to do with allowing air ingress into the cylinder, which is achieved purely through the barrel/nozzle or in combination with a cylinder port.

You can see this in the true fit of the o-ring in the piston head where there is no back and forth movement, as shown in your lower diagrams.

In my opinion, piston head porting purely allows compressed air, from the forward stroke of the piston, to be directed in and against the piston o-ring making a tight and efficient seal against the cylinder wall.

Still, a good mod to save a few bob.

<{POST_SNAPBACK}>

Please bear in mind that my drawing of how the porting works was made deliberately exaggerated in order to clearly show what otherwise would have been too small to perceive. While the drawing is mine, the concept is not. Its a copy of a similar diagram found in one of the early issues of Airsoft Tuning Guide. I did not come up with the porting explanation entirely on my own - I lifted it off from the Japanese.

 

While the o-ring is, as you say, a true fit.. it's by no means a tight fit - there is some movement (as pointed out in the original Japanese material) enough to allow air to pass as shown in the diagrams. The o-ring always seals against the gap between the piston and the cylinder regardless of the direction of travel. That is why an unported piston is almost impossible to pull, or draw, backward if the air nozzle is completely blocked - vacuum is formed within the cylinder. Yet, a piston with ported head can easily be drawn with hardly any resistance. If the front opening was totally shut, where else did air pass into the cylinder to negate the vacuum?

 

None of what I have so far posted here is by conjecture or guesswork. Most, if not all, of it has been researched and backed up by close to 20 years experience as an airsoft gunsmith.

[Tommygunn]

It just seems odd to me that you would allow air in from that direction. Firstly because it seems to be very restricted and there are other means for air to enter but also because of the amount of grease present. I personally always smear grease around the piston o-ring and a film of it around the cylinder inner. Now I would have thought considering the speed the piston retracts then a considerable force of air is passed around the o-ring which I would have thought would blast grease into the cylinder cavity and also into the nozzle, hop etc. Obviously this has its negative effects.

[Marlowe]

Well, I wish you all the best in this modificiation. The use of such a head in Systema Bore-Up sets has been a source of woe for me for some time, with the expanding and contracting o-ring succeeding in perishing enough to simply flop from the piston head, and the ensuing nightmare of attempting to locate an appropriate head. Personally I would much rather have the stock piston in - had that not disintegrated too.

 

However it is your gearbox, and so I wish you the best of luck, and hope you don't experience the same issues I have.

[systema]

 

Hey Almighty,

Nice to see you're posting here too

 

Anyways, I'm trying to understand the mechanics of the piston porting as you've been describing. Is it not true that in figure3, that the drawn air would also exit from the holes from the porting? Or is that amount of air insignificant to the quantity that was drawn in the first place? I'm assuming that when the piston is drawing, there is more time to draw air then when the piston is released, and that most of the drawn air from both the ports and the nozzle is exited out of the air nozzle. Is this correct?

[Almighty]

I personally always smear grease around the piston o-ring and a film of it around the cylinder inner. Now I would have thought considering the speed the piston retracts then a considerable force of air is passed around the o-ring which I would have thought would blast grease into the cylinder cavity and also into the nozzle, hop etc. Obviously this has its negative effects.

<{POST_SNAPBACK}>

You are correct about the gear issue. If, as you say, a liberal amount of grease is applied to the o-ring, then it will surely get carried into the cylinder cavite and blasted out thru the air nozzle and into the barrel, drastically affecting BB velocity as well as flight characteristics. This would happen not only with DIY ported piston heads but with Japanese original ported heads as well. IN fact, the same can also happen to overgreased unported piston heads. That is why, as a rule, we keep grease to a minimum when it comes to the piston and the cylinder. In some instances, we even resort to wiping down just to keep grease from fouling the bore.

[bignaz]

did this on a stock utg and seen a 25fps increase overall. the gun is now in the low 280's on avrage.

[cazboab]

Porting the piston head shouldn't have done that Naz, maybe something was out of place slightly and you nudged it into the proper position when re-assembling.

 

Personally, My view is, it doesn't do anything, unless maybe your barrel length was borderline for the piston your using, but the only experience I have with a ported piston head is the Laylax one in my L85, which now works only due to me filling in the holes with rubber resin, and really common sense says holes mean leaks so you will get a slight drop in pressure from them, regardless of the "increased" pressure created by the "extra" air the piston head is supposed to let in.

[Hissing_Sid]

If the design concept made no difference, then why are 99% of aftermarket piston heads ported?

<{POST_SNAPBACK}>

Don't get me wrong. I think it's a good idea and your little write-up on how to do it is very well-written and readable.

 

The reason 99% of after-market pistons are ported is probably cos, in the world of airsoft, people buy stuff that they perceive to be an "upgraded" part rather than a standard one.

 

Systema haven't stopped making their eliptical gear sets, you can still buy 6mm ball-bearing bushes and TK is still knocking out twist barrels. Somebody must be buying all this junk or it wouldn't still be made.

[Almighty]

My view is, it doesn't do anything,..

...and really common sense says holes mean leaks so you will get a slight drop in pressure from them, regardless of the "increased" pressure created by the "extra" air the piston head is supposed to let in.

<{POST_SNAPBACK}>

It's common sense enough also to test for leaks by simply taking the cylinder and piston, plugging the nozzle and trying to compress the trapped air inside.. while submerged in a basin of water. In as much as o-ring may perform differently during fast and slow compression, do it both ways just to be sure. If a stream of bubbles appear and the piston "bottoms" out, then maybe the holes leak as you say they would. So far, it has not happened to us.. yet.

 

Don't get me wrong. I think it's a good idea and your little write-up on how to do it is very well-written and readable.

Thank you.

 

..in the world of airsoft, people buy stuff that they perceive to be an "upgraded" part rather than a standard one.

 

Systema haven't stopped making their eliptical gear sets, you can still buy 6mm ball-bearing bushes and TK is still knocking out twist barrels. Somebody must be buying all this junk or it wouldn't still be made.

<{POST_SNAPBACK}>

I quite agree. For most part, my recommended upgrade buys stop at metal bushings and the spring. Practical experience has shown that the cost of air seal nozzles, bore up kits, spring guide w/ bearings, TN barrels is not justifiably proportionate to (relatively small) increase in performance.

 

Still, empirical results and experience should carry some weight. Explainable or otherwise, actual performance is hardly debatable. We wouldn't keep on reworking pistons if doing so amounted to nothing all this time.

[Sale]

The majority of upgrade piston heads are ported, because they are intended to be used with upgraded nozzles, which require a ported piston head.

 

Tommygunn is right that the pressure directed to the O-ring in the compression stage improves seal. So porting the piston head actually has more benefits than just easing the air intake phase.

 

Comparing a ported and stock piston head while handling the parts backs all this theory up. It lets the piston move back more easily, and provides a better seal when going forward. If it doesn't work like this, there is something wrong with the parts.

 

It's definitely an effective upgrade, not a matter of faith. Remember to keep grease to a minimum. It's only there to prolong the life of the O-ring, and excess amounts will actually slow the piston down, as well as get into the barrel and cause problems. I usually use a drop or two of silicone oil, and completely whipe the inside of the cylinder free from grease.

 

-Sale

[Almighty]

Tommygunn is right that the pressure directed to the O-ring in the compression stage improves seal. So porting the piston head actually has more benefits than just easing the air intake phase.

<{POST_SNAPBACK}>

No debate from me on this. Though I had not dwelled on the improved air sealing during compression.. notice that in the drawing, beside the o-ring are little arrows indicating o-ring tendency to expand due to the air compression. I am glad to see someone agree that there are indeed benefits to this mod.

[Zephyranthes]

Well I can't really say this post really helped me because I knew that, but good work. I've been doing those on all my own AEGs, and all my customers who get their AEG upgraded from me.

 

My AEG is so incredibly air efficient, if I do the compression test, no air leaks at all.