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combustion pressures

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combustion pressures

Unread postAuthor: splat » Mon Sep 25, 2006 9:10 pm

Hi all, newbie here with a 1 day old spud gun, already have bigger-better-itis. So I'm seeing what I can do to really blast some taters. I grabbed another cleanout cap today and put a spark plug anti-fouler in it and have been using an auto engine compression gauge. I've seen as much as 42 psi.

Basically I'm wondering if that's a decent number, or even too much for my sch 40 pvc.. seems to be fine, but who knows if that number's really accurate as the spike may be more than the gauge can read?

My best shots so far have been nitrous and Mapp gas, the potato literally goes till I can't see it anymore but I'm getting the same peak pressure reading as the other, still visible shots.

Am I going about this the right way?
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Unread postAuthor: ProfessorAmadeus » Mon Sep 25, 2006 9:14 pm

Well dont use an oxidizer like notrous anymore and just use the mapp gas. For the distance, one spud probably had a better seal than the other one. Thats about the average pressure it sould make. If you want to make something better may i suggest a pnuematic gun?
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Unread postAuthor: splat » Mon Sep 25, 2006 9:29 pm

Is nitrous dangerous in these? I know it doesn't burn by itself, but it does put a nice frigid blast into the warm PVC.
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Unread postAuthor: carlbelcher » Mon Sep 25, 2006 9:32 pm

Think of it this way:

Your combustion = ~42psi

Basic pneumatic = ~100psi

Also are you seriously using NOS?
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Unread postAuthor: splat » Mon Sep 25, 2006 9:51 pm

No, my N2O kit came from NX, not NOS.
Anyway, I'm giving a couple second shot into the open 3" chamber.. just enough to see the white plume enter the chamber. Then 14 seconds of MAPP through the torch head, cap within 5 seconds.

And I know pneumatics always win, but I like the booms.. I wonder about increasing fuel efficiency while staying in the safe zone, hence the pressure gauge. I didn't know if MAPP was gonna spike through the roof or what. Frankly I was disappointed w/ MAPP until I gave it the N2O, it really seemed to wake it up. Haven't accurately measured range yet but it looks close to 1000 feet.
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Unread postAuthor: Jolly Roger » Mon Sep 25, 2006 10:36 pm

How are you measuring the fule ratios? Technically with MAPP gas, you could achieve alot higher pressures (Past 200psi) but they are not realistic. If you make a fuel meter using burnt lake (search) you would increase your fuel efficiency greatly. There is no need for oxidizers if you get this step right.
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Unread postAuthor: splat » Mon Sep 25, 2006 11:01 pm

Reading up on metering systems right now..

I'm not accurately measuring the ratios, just as I described above. A fog of this, spray of that..
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