90% Bore porting Revisted. Marauder @ .23"

Forums PCP Airguns 90% Bore porting Revisted. Marauder @ .23"

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    ackuric
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    So I couldn't help but try again, this time the goal was as per the original goal I had, to keep the OEM seat intact and port the valve to 90% or greater. It was actually really easy…but I can only say that after failing and learning from the experience.

     

    My first step was to drill the throat to .2345". I used the stock spring retaining cap as a centering tool and went from .203" to .2188" and then to .2345". I then took it to .237" and later polished it really well which likely brought it to around .238". My error on my last attempt was not doing this prior to drilling the exit port. I thought about plugging the stock port to create more resistance for the drill bit to help stay centered but I figured using the spring retainer cap plus not drilling the valve exit port first would both suffice, which they did.

     

    Picture 1 shows the valve throat drilled to .2345" and the valve seat sanded down to remove the 'rim' creating more of a flat spot which is larger than my poppet od of .275":

    20181129-181611

     

    My second step was to drill the valve exit port up to .203" at a negative angle, the degree was minimal, between 5-10…almost straight, and then dremel it the rest of the way as I desired which ended up at .226" front to back, and .234" side to side, making a .23" port. 

     

    Picture 2, 3 and 4 are of the valves exit port after being opened up. (You can see the minimal degree / cant required to achieve my porting in pic 2 on the calipers.)

     

    20181129-181632

     

    20181129-181753

     

    20181129-182019

     

    I also removed .1" from the back of the valve as I prefer to create more throw than the stock marauder which aids in reducing required spring/hammer energy. I also ported and polished the surfaces really well after the pics were taken, using 600 grit and following up with automotive polish. 

     

    Right now the valve is just setup in my test rig for holding pressure, which so far it is, but I like to give thorough testing prior to tearing down my rifle and swapping valves. I'll let it sit over night and test fire it a bunch in the test rig and see where it starts to let pressure go as I am running a peek poppet and they can be stubborn at low pressures. I will likely have it up and running by this weekend hopefully with a shot or two over the chronograph that edges passed 900 fps, which isn't shabby considering my reg pressure is JUST shy of 2000 psi and I run the stock marauder length barrel of 19.5". This will all be done on just 7.7 lb of hammer spring and 48 gr of hammer. I have a 29 gr hammer that I could alternatively use but it requires 11-12 lbs of spring.

     

    But there you have it, I knew a marauder could be taken to .23" without moving the seat forward, I didn't intend to go to .23"…it kind of just happened. I have .05~.06~" space between the valve exit port and seat which should hold up great. That is at the edge, it increases in thickness gradually as the angle in the porting changes.

     

    ***Note porting to .23" with only .238~" throat requires a .04-.045" valve stem, do not modify a stock valve stem in attempt to copy this. Upgraded materials required. Do so at your own risk***

     

    -Matt

     

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    spysir
    Participant
    Member

    Ya just had too huh.

    And thank you for sharing pictures along with detailed information.

    John

     

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    ackuric
    Participant
    Member

    Yea, well…a guys gotta do what a guys gotta do. When you know something can be done better than you had done before, you tend to have an itch until getting it done. The only thing I didn't do on this valve compared to my last was hog it from .42"~ to .5" from valve entry to seat, which IMO is only really good for volume, which I do not lack or currently need. If I find myself on the edge of 900 fps @ 899.9 or something I would tear down the rifle and hog it out lol..but my .214~" ported valve isn't hogged out either and hit 891 so I don't think it'll make much difference for me. My plenum volume is 53 cc, the extra volume available in valve is 1 cc, which is just under 2% increase. If I were at say 20 cc volume then that would be 5% which would make it more worth it, at least IMO…so thats why I didn't bother.

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    ackuric
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    Welp, I hit my goal, as I said I wanted to edge passed 900 fps with 33.95 MKll's on 1990~ PSI of air regulated using a marauder 19.5" barrel. My calculations put me RIGHT there. And what do ya know? I hit 901.7 (902 fps)!  My calculated peak put me at 904~ fps.  Accurate within 99.77%! Consider myself tickled pink. I didn't lean on the spring to see if there was another fps or two, or take any more shots as there can be mild fluctuation at peak. I am happy enough knowing I did what I set out to do and am in celebratory mode! This was done with 7.7 lb of hammer spring and 48 gr of hammer, as I said it would be! :D

     

    20181130-171134

     

    Also picture of gauge for anyone in disbelief. As you can see its shy of 2,000 psi, likely right around 1990 or 137.25 bar, but thats just a guess..this gauge was calibrated @ 2k psi against my liquid filled gauge which  is accurate within 1%.

     

    20181130-172224

     

    -Matt

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    Bigragu
    Participant
    Member

    That’s awesome, Matt. I can’t remember, whose reg do you have in that thing? I apologize for not getting back to you with a sample shot string. Son got me sick, slowly getting over it.

     

    i always read up on folks like yourself messing with a “PEEK poppet”. Where does one obtain this material? Is there a parts place other than our vendors that one can source these specialty materials?

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    ackuric
    Participant
    Member

    Lane regulator.

     

    You can find 1/4" or 3/8" peek on eBay for fairly cheap, I prefer 5/16" rods which are harder to find. Acetal is much more readily available and is VERY comparable and even easier to get to seal so its not a bad alternative, much cheaper too.

     

    My valve stem material is made from 1/8" HSS blanks, and then thinned down to 1mm in all the areas that goes into the valve throat. I am still testing strength on this arrangement, but I've had a similar .215" ported valve with 1mm valve stem  run for over a year with it. 2mm is WAY safer and would be without question strong enough for upwards of 3k psi, at least IMO. I don't really advise people to do as I have done, because it is pushing the limits, but thats what I am here for, to be a test dummy. My .215" valve with .26" poppet had 107 lbs of force against the poppet head when the valve is closed, where as my .23" valve with .275" poppet has 120 lbs of force on it when the valves closed. I did increase the OD of valve stem 10% from .04 to .044 when going from the old valve to new valve to compensate for the 10% increase in opening force required. IMO the stem should hold up fine for me.

     

    My setup also has a HUGE plenum extension, 33 CC's. Without that extension I would be at 20 CC's of plenum. A Whopper of a difference. The 20 CC version of my setup would likely only make 890~ FPS at best. Not a HUGE difference being 12 FPS, the smaller plenum would require me to raise the set point 100~ psi to compensate.

     

    -Matt

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