Compressed-air pinewood derby car

MAKE subscriber sliptonic wrote in with his enhanced pinewood derby car:

I built this car for the open class of my son’s Cubscout pinewood derby race. It uses a 9V solenoid to release pressure from a PET bottle. I won, despite a minor design flaw.

The flaw being that the bottle didn’t fit under the finish line banner — but only the nose has to cross the line to win.