For those who don't know, the Pinewood Derby is a gravity powered race of home made cars fabricated from small lightweight blocks of wood with plastic wheels. They run down an inclined track. Usually a track has four lanes.
Our pinewood derby track has IR sensors at the end of the track and a serial interface that connects with commercial software that will track times, scores, speed to scale in miles per hour, organizes the race order, etc. Our track is 4 lanes and has 1 large 7 seg. display per lane that shows the finish order. All the timing, etc is displayed via the software on a laptop thats connected to a projector.
The IR emitter for each lane is placed below the 7 segment displays at the finish line and aims downward to a small drilled hole in the wood that contains a recessed IR detector.
In addition there is an IR beam across the tracks at the start line that triggers the counter to start. Hopefully this information helps. Sorry, but the name of the software escapes me right now.