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MAPP gas question

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Unread postAuthor: Technician1002 » Mon Jul 06, 2009 9:22 pm

Budarooski wrote:
Moonbogg wrote:Screw it. Start with 5% then tweak from there.


That's funny...that's what I was thinking. :)


This is often recommended as some space in chambers is estimated. The actual chamber ID may be slightly larger or smaller than assumed. The volume in the reducers, elbows, and other parts is often a guess. Volume taken up by fans, spark strips and such are often unaccounted for in the volume calculations.

Tweak for best performance and lock it in. Pressure gauges are another source of measurement error.
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Unread postAuthor: Moonbogg » Mon Jul 06, 2009 9:40 pm

Technician1002 wrote:. Pressure gauges are another source of measurement error.


Are you referring to them when they are inaccurate? Or perhaps when one might be hard headed about using the correct reading since its what the calculations tell you is correct? I suspect maybe both :lol:
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Unread postAuthor: inonickname » Mon Jul 06, 2009 11:27 pm

If you want your exact chamber volume, then fill it with water. A good ratio for mapp is about 5%, I believe it's a tiny bit higher.
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Unread postAuthor: Technician1002 » Tue Jul 07, 2009 8:12 am

Moonbogg wrote:
Technician1002 wrote:. Pressure gauges are another source of measurement error.


Are you referring to them when they are inaccurate? Or perhaps when one might be hard headed about using the correct reading since its what the calculations tell you is correct? I suspect maybe both :lol:


I suspect you are correct. Anyone metering by calculations only is missing the adjustment phase. I have 2 100 PSI gauges. When one reads 100, the other reads 92. A little trial and error can go from the might be close to tuned to peak performance.

In the t shirt launch coemptition, we did some calculations, and then took a bunch of measurements. Which works better? 2 inch, 2.5, inch 3 inch, 4 inch? 5 feet, 6 feet, 7 feet 8 feet? 30 PSI, 40 PSI, 50 PSI, 60 PSI? We have a stack of graphs from tests and picked a solution that can literally hit any area of the Rose Garden Arena, including the back row of the 300 section.

We guessed the long 2.5 inch barrel would be the best one. I even gave it the best paint job. We were wrong. Without testing, we wouldn't have known.

Is your mix at the peak? Have you tested?
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