Trying different setups for this to simulate a radial type engine. The original bottle I tried looked to long and not enough diameter. So I used that as the mount for a slightly larger bottle. An extra 1/4". Made the outside bottle shorter and think it does look better. There are air holes in the inner bottle to vent the motor. Of course, all this is subject to change!
Inner medicine bottle used for mount support for the otther bottle above.