Ahh, the yearly "performance" vs. "efficiency" thread.Labtecpower wrote:jackssmirkingrevenge wrote:Anything above 1:1 is going to be bad for performance, for a combustion you want the chamber to be between 0.9 and 0.5 times the barrel volume.
It could be that a larger chamber would have performed the same or better with the same barrel as the small chamber. Or am I wrong?
Performance and efficiency are not the same thing. And there are many ways to quantify both.
Efficiency is, in the combustion spud gun world, totally irrelevant. Latke's CB of 0.8 is the most efficient one. That means the largest percentage of the energy available in the fuel is converted into kinetic energy of the spud. He started with a fixed chamber size then changed the barrel length until he had maximized the muzzle velocity. If he would have then take the most efficient barrel length and put it on a larger chamber the performance would have gone up, but the efficiency would have gone down. But efficiency is irrelevant, so by any logical view of the matter a chamber bigger than CB 0.8 is better.
There is a a point where a large enough chamber will actually start to decrease muzzle velocity for a given barrel and ammo. I don't think anyone really knows what that ratio is but it is certainly well above a CB of 5:1.
Bottom line #1: Make the CB bigger than 1:1 but anything above 1.5:1 is getting into greatly diminishings returns.
Bottom line #2: There are a number of much better ways to significantly improve the muzzle energy (i.e., the only "performance" you really care about), and Bottom Line #1 isn't even on the list.
In rough order of biggest improvement to least improvement:
1. Meter your fuel: Figure that will double your muzzle kinetic energy (on average). And, your shots, and ignition, will be much more consistent.
2. Include a chamber fan: Figure that will also double you muzzle kinetic energy, particularly if you are impatient. (Or, omit the fan and just let the gun sit for a few tens of minutes before firing.)
3. Increase both the sealing capability and static friction of the ammo to the barrel. This is easily done for spud ammo by beveling both the inside and the outside of the barrel when making the spud cutter. You want a tight seal and a fair amount of static friction.
87. Optimize the CB ratio