Will tank size on a engine test stand make a difference on breaking in different engines? I have a test stand with a 10 oz. tank and only recently thought of what difference it makes depending on engine size you are breaking in. After breaking in many 40-80 size engines and a few bigger 120-140 size engines it was pointed out to me the larger engines may be running richer than expected due to higher tank pressure from the small tank. Should a engine be broken in on the test stand with the same size tank used in the airplane? Thanks.

Smaller tank size means higher pressure, resulting in rucher than expected? Hmmm, this is a good one. For most setups you use an exhaust fitting to pressurize the tank. This pressure would not vary based on tank size. Furthermore, you control the fuel mixture with the needle valve. If for some reason the smaller tank really was resulting in more fuel flowing to the engine you would just set the needle valve a bit more lean. The value of using the same size tank as you will use in the plane is to be able to measure run times.

There must be a connection to tank size since the Magnum 80 engine specifically calls for a 12-14oz or less tank , otherwise a lean run will occur. This is stated in the manual and does seem to effect operation. I will contact the manufacturer and post some more information on it once I find out a little more info. Thanks

piper_chuck, I think you are missing something,

Let say you have 10cc void with 12oz tank and want to increase to 1.5 atm so with PxV=nRT you need n= 0.5atmx10cc/(RT) amount of air/exhaust gas,

If you have 20cc void with 24oz tank than you are looking at 2 times more air/exhaust gas to achieve the same pressure.

The importnat thing is not whether the muffler can provide this much pressure, it will provide it at the end but how long will it take it achieve that presssure? about 2 times more time (roughly). So the engine might lean out becuase there is not enough pressure in the tank when large tanks are used.

The flow of exhaust gas from the muffler is same on both cases.

Altough small tank will not run rich at the steady-State with a big engine but the transition will be richer as it will be able to increase the pressure in the tank rapidly and pump more fuel quicker, it might result in richer run and transition.