SpudFiles

When i measure the chamber do i measure the (2) 90 degree elbos as well?

depends where the valve is... if its on top then yes if its on the bottom then no...

If part of chamber yes

if not then no.
please think before you post

-e1337

It looks like this...

yes it is part of the chamber since there is no valve because it's a combustion. It's part of the chamber because the potato will only go down and stop at the elbows.

I've never bothered to measure the volume of the elbow, reducer, or other fittings. I just don't think theres a need to be that precise with a combustion. All my guns have worked very well. I use a 1.5:1 loud as hell and powerful. It rocks.

When i measure the chamber do i measure the (2) 90 degree elbos as well?

Depends on what you are trying to do.

Trying to get a big bang and a spud launched a long way? Then no, you don't need to measure the volume of the elbows.

Trying to get the launcher to work as well as it possibly can? Then yes, you should either;

1. Measure (or estimate as well as you can) the volume of the elbows and add to the volume of the chamber. Calculate the amount of fuel based on the total volume.

or

2. Fire the gun with varying amounts of fuel until you get the best performance.

One challenge with an over-under combustion design is getting the fuel to mix with the air all the way around the bend and up to the spud. A fan will help but it will still take a while to get the fuel around the bend.

ALIHISGREAT wrote:depends where the valve is... if its on top then yes if its on the bottom then no...

Combustion discussion......

@jimmy101
Indeed the fuel should be mixed all the way up to the spud to get the right fuel ratio.
If the fuel doesnt mix all the way up, you got too much fuel in the chamber.
Not that it matters much, but it does apply to the "Trying to get the launcher to work as well as it possibly can?"
So you should have to wait longer for the fuel to mix in that case.