right ratios

Boom! The classic potato gun harnesses the combustion of flammable vapor. Show us your combustion spud gun and discuss fuels, ratios, safety, ignition systems, tools, and more.
kimmimaru1227
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Thu Dec 20, 2007 9:11 pm

i was wonderin about my gun and a problem arose..... need the right propane to air ratio..so if anyone knows it plz tell.
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hi
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Thu Dec 20, 2007 9:22 pm

well, how are you measuring it? do you have a a meter or are you just spraying it in with a torch head?

if you have a meter you can use this to calculate the exact amount of fuel needed. http://www.burntlatke.com/ratcalc.html


if you are just doing the old "spray and pray" method, then keep spraying and keep praying... 8)
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you know you are not an engineer if you have to remind yourself "left loosy righty tighty"
cwazy1
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Thu Dec 20, 2007 9:25 pm

its like 4.2% for propane and 4.7% for mapp
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mark.f
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Fri Dec 21, 2007 9:29 am

4.89% for MAPP, I just round to 4.9%, but 4.7% is a little lean...
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bigbob12345
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Fri Dec 21, 2007 9:56 am

No its closer to 4.7 for MAPP than it is to 4.9
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jimmy101
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Fri Dec 21, 2007 12:42 pm

Check the Spud Wiki page on various fuels
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King_TaTer
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Fri Dec 21, 2007 12:55 pm

this is understandable since you are new to this site. but from now on try searching on your own first, like in the wiki, before asking. tends to annoy the mods when this happens haha :lol: .

anyway... if you haven't invested in a metering system i suggest you do so as it will be much easier than guessing. good luck.
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octane89
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Fri Dec 21, 2007 1:21 pm

On the wiki, I thought mapp was 4.6%?
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mark.f
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Fri Dec 21, 2007 1:56 pm

It is.

I sat down and calculated MAPP percentages last year based on average percentages of different gases from information from Bernzomatic, and got 4.89%. Regardless, BurntLatke's tests show 4.6% is around optimal.
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boilingleadbath
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Fri Dec 21, 2007 4:01 pm

Ya know, there's a fairly good chance that the 4.9% test velocities where actually higher than the 4.6% tests... latke's data had a large standard deviation, and his averages in question aren't very different.

I think the probability that the 4.9% is better is 26.5% (T-test), but I really don't know as much statistics as I'd like to.
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