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Menace 04-09-2009 09:42 PM

Valve and bolt tweak

With the advent of warmer weather, I've got the tinker itch again.

For giggles, I'm thinking of tapping and capping all the holes in the valve that aren't actually in use, just to see what it does to the efficiency and velocity.

This would obviously be done on a spare valve.

Has anyone here actually done this, so as to give some commentary on the mod?

EDIT: Also, it would appear I'm the only person on the planet who hasn't opened up the valve to 3/16". Any clue as to the velocity/efficiency change this will bring?


HP_Lovecraft 04-10-2009 09:06 PM

Thats the first I've heard of that, and I don't see anything wrong with that idea.

Thats how the aftermarket magnaport valve was setup. One large hole, and nothing else for max effeciency.

Even if its not a spare valve, I don't see much risk. Especially if your drilling/tapping the 3 holes that nobody ever uses. Worse case scenerio is you just remove the plugs.

Menace 04-11-2009 01:08 AM


A new one for HP?

I'm floored. ;)

It seemed like a non-harmful idea, and I was of course hoping for a bit of boost in efficiency and perhaps velocity as icing on the cake.

Did the Magnaport valve provide a meaningful difference over the stock valve? Now I'm curious about that. No doubt they cannot be had for cheap anymore, eh? Still, it's more fun making your own.

And to refrain the second question, big hole at 3/16"---what changes can be expected from this? If each hole size represents roughly 40 fps increase, would it be fair to expect the same for the larger hole?

HP_Lovecraft 04-11-2009 07:24 AM

The amount of increase is limited by the valve channel that transfers the air from the valve to the valve. It acts as a bottleneck.

Earlier VMs had a smaller hole, while the later ones had larger holes.

Menace 04-11-2009 01:41 PM

Ah, yes, the bottleneck. That was another question, whether 3/16" would match, or overreach the original hole.

Clearly I can determine a maximum diameter, but before I go through the hassle of fighting Loctite to measure, do you happen to know (a) roughly when the switch came (I'm assuming we are talking about changes in the VM itself, vice change from PMI-III to VM), and (b) the size of the larger hole?

EvilEd 04-13-2009 08:36 PM

Ok plz do before and after tests and pix of the mod and send them my way and I post it on the Vm Empire

Menace 04-15-2009 01:57 AM

Oh, great!

No pressure now!


(Will do, though it may be a week or two yet. Mucho busy this time of year. I'll PM ya with the goods. ;))

Anonymous Coward 04-17-2009 08:35 PM

My bet is plugging the holes will give you to small of results to matter. Remember all flow travels though the least amount of resistance. You are talking about very tiny holes that go nowhere.

But increasing the size of the valve's port will, though you run the risk of countering the blow back force needed to recock the hammer.

I'd like to know if you elongate the bolt's valve input port so that the bolt and the valve ports match up sooner, will you get a boost? But is that removing the small shock buffer the hammer needs to not wear down against the valve?

Take out the screw plug for the valve port behind the feedblock. Then use a marker and put a matching size dot on top of your bolt right above where the bolt's valve input port is. Then manually work the action of your hammer and you will see at what point your bolt's input valve port aligns with your valve's output port. You'll feel when the hammer hits the pin and when in the depression cycle the two line up. That better explains what I'm talking about. Then measure the distance traveled when the hammer hits the pin to when the two ports just start to line up. That's the initial sock absorption buffer zone. Then measure the valve pin's lip length that allows the CO2/HPA to slip around the valve and push back the hammer. That should tell you how much you have to play with in that buffer zone.

Having the hammer slam into the valve over and over will really mess an aluminum body up over time.

You might look into getting an open faced bolt over the center fire bolt to increase FPS. It's the easiest drop-in increase for FPS I've seen. Mainly it does not restrict flow and places the full gas blast across a much larger surface area of the ball at initial contact.

Menace 04-18-2009 11:03 AM


You raise some interesting points. However, I'm still betting that, given that so much here has to do with volume, pressure, and time, the plugging of the ports will have more than simply a minimal effect. Even though they do go nowhere, they increase volume and decrease pressure inside the valve.

Besides, the mod is already finished! :gunsfiring:

I'll be posting more on that soon.

I want to think more about your slotting of the top bolt. Most intriguing, but may be too good to be true. A number of things seem to speak against it being very effective. Also, I've not considered the "shock buffer" scenario you paint. I'll look at that more closely. You may well be correct.

More to come!

Menace 04-21-2009 09:40 PM

3 Attachment(s)
Well, gang,

Here are the pics of the mod, as promised. After it's tested to my satisfaction I'll be posting more specific data to Evil Ed for use on VM Empire (assuming this thing passes muster). In that event, I will be including all technical information, boring stuff, etc.

Here's the test valve, all small holes freshly bored (I maintained the large hole, as I wanted to test it as is, to keep variables to a minimum. In time, further tests will likely be done, and their results included). He's wearing a bandit's garb and some internal plugging to keep out as much junk as possible. Besides, it makes him look mean!

Attachment 8401

Here he is, having been tapped for 10-32 threads, with a stock friend for comparison.

Attachment 8399

And here he is again, having been plugged with 3/16" cap screws. You can see the blue Loctite on the left side. If it looks as though the cap screws are really short, or in really deep, there is a reason for it (though some of it is is an optical illusion). But more on that to come.

Attachment 8400

Again, these are just the pics, to whet the tinker appetite. There's more that's been done to our friend here, but I don't want to give away too much (read: put your stuff at risk if you unwisely follow suite) until things have been properly tested.

With that in mind, be advised NOT to try this (unless you have spares and just don't care) until this is fully checked out. I don't want any of you annoyed with me for having ruined your baby.


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