SpudFiles

in a week or two im going to make a large cannon with a 4" x 24" chamber and a 2" x 5' barrel, it will most like be a "spray and pray" cannon and i was wondering how much a chamber fan would help

Quite a bit. I wouldn't be able to quantify it, but it would mean that the amount of fuel you need was more consistent so easier to gauge.

it gives you a "huge" increes in performance!

It increases the power of you gun by 30-50%. Thats ALOT.
It mixes the fuel with the air, vents out the cannon faster for fresh air (thus oxygen) and last but not least: it creates turbulence making the fuel burn faster.

After upgrading my cannon with a chamber fan and a second spark gap, it increased the power of it so much, that instead of shooting a spud against a plywood board making it splatter, the spud went straight trough the board AND my barn door.

@Biopyro
I dont exactly get what you mean with that?
You mean that when it is mixed your amount of fuel is more consistent since it doesnt all sit in one place of the chamber?

thanx a bunch, ill get 1 then

Yes a fan makes a difference and use 2 or 3 spark gaps roughly equally spaced in length and down the center of the chamber. That will add performance in that relatively long chamber.

All a noticable difference in performance.

Psycix - yeah, basically, the mix is consitent throughout the chamber. Without a fan there might be the correct concentration between the electrodes, but not enough or too much in the rest of the chamber, making it less powerful.

In my experience it's not the size of the fan but rather the fact that it's there. You are just moving a small amount of air for venting and mixing. Place it close to the end for easy access for easier mounting and cleaning.