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C:B ratio 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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C:B ratio question

Unread postAuthor: psycix » Mon Jun 25, 2007 7:56 am

Hi guys,

I just came on this forum today and I have a question about C:B ratio.

Im planning to build my first real combustion spudgun soon.
Now i have read alot about ratios and some people say 0.6:1 is best, some say 0.7:1, 0.8:1, 1:1 or 1.5:1

Now i know a ratio thats too small will ruin the performance, but will a too high ratio do too?
Now when i just go for performance (projectile speed) and dont care about wasting fuel or energy or making too much noise, then what would be the best ratio for me? (im thinking to use a 1,5" or a 2" barrel, both about 1 meter long (3-4 feet)

bye,
psycix
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Unread postAuthor: jimmy101 » Mon Jun 25, 2007 5:38 pm

Any CB ratio in the range of 0.5 to 1.0 will behave about the same. Really doesn't make all that much difference. (See Latke's 1.5" data for example.)

The two things that will make your gun perform the best are (1) a chamber fan and (2) some kind of a fuel metering system. Both of those mod's will do more for the performance of your gun than will getting the C:B ratio exactly right.
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Unread postAuthor: psycix » Tue Jun 26, 2007 4:21 am

thanks for your answer and thanks for the scheme :)
my first real comb spud was planned to have a 1:1 ratio
i see now that .8 may be better but indeed, it doesnt really make much difference

so ill keep it that way :)
well thanks again :D
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Unread postAuthor: SnowFlox » Fri Jun 29, 2007 12:38 pm

how do you calculate a C:B ??

i dont get it... :(
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Unread postAuthor: SpudBlaster15 » Fri Jun 29, 2007 12:50 pm

Divide the chamber volume by the barrel volume.
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Unread postAuthor: SnowFlox » Fri Jun 29, 2007 12:52 pm

omg... i get it.. thanks !
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