don't know how many cars, but on my 8'x 12' train board that I take to shows, I had a continuous train around the entire outside loop. the rear coupler of the caboose coupled with the front coupler of the lead locomotive. so 8+8+12+12= 40feet or close to it.
one lady stood there and watched for about 5 min before she realized there was no end, she says.
"there's no end to this train"