Best Ratio

[Fight The Machine]

What is the best C:B ratio for massive, awesome power on a combustion spud gun? I'm talking super distance and knocking down trees powerful...

[boilingleadbath]

To determine the most powerfull volume ratio (max power for a certain overall length) you have to examine your chamber's DIAMETER and your barrel's DIAMETER. For a propane fueled launcher, it hits bottom at .6:1 (volume) at a 1:1 (diameter), and increases as the diameter ratio inrceases. For instance, a 1.5" barrel, 4" chamber (2.7 diameter) wants roughly a 2:1 (volume) ratio, 'cording to a estimation using the GGDT.

[longshot1068]

My big combustion is running a C:B of 4.5:1- 4"diam chamber and 1.5" diam barrel and im landing them 600 feet out with 4.2%volume. not super distance but fun and loud just the same.

[jinxd]

BurntLatke proved that 0.8:1 was the best, IIRC

[Velocity]

yeah, jinxd is right...

0.8:1 C:B ratio is best for propane powered combustions
1.5:1 C:B ratio is best for aerosol powered combustions (not 100% sure why, probably has something to do with the burn rate)

This is kinda off topic, but I think 2:1 is the best ratio for pneumatics


and i dont think you will be knocking over too many trees, no matter how perfect your ratio is

[Mihlrad]

i would go at least 2:1. or smaller on the barrel bigger on the chamber, all ratios aside, its common sense that bigger chamber + smaller barrel = more power.

As for knocking down trees, i would say go for a 36" diameter barrel to fit wrecking balls in along with a 144" barrel, that holds about 6 propane tanks in it, along with massive amounts of extra air, say a 10x mix or so? Give or take 1 mix? Than you will certainly be knocking down trees. Best of luck, if you build it be sure to post it.

[FiveseveN]

Would somebody stick this? There's a C:B ratio topic every 2 weeks or so. This one looks like it's got all the good info.

its common sense that bigger chamber + smaller barrel = more power

But there's a limit. 1st of all, a tiny barrel might constrict gas flow enough to make the chamber go boom. Depends on the chamber's geometry, material and the fuel you're using, but it's something to keep in mind.
I've tried 4.5mm barrel with a 37mm chamber (IDs) and it had negligible power.
So going over 3:1 will probably just be a big waste of fuel.

Also, here's the Spud Wiki page on C:B ratios: http://www.spudfiles.com/spud_wiki/inde ... rrel_ratio

[mark.f]

Actually, if you build it right you can completely close off the chamber and ignite the mix inside it without anything happening. Only 50 PSI max.

Jspellman did a closed chamber ignition with a 4x/4x atm mix on his hybrid.

[LucyInTheSky]

I wpuld say with a fixed barrel length then make the chamber as big as you want, But never shorten the barrel to get a higher ratio.

With a fixed chamber length then make go with 1:1