For my brother's birthday, I was going to do a racetrack cake. (Thankyou, Kathy164 for the idea!) But... how do I make a racetrack. Note, I can't use fondant or anything, only BC. Do I use graham cracker crumbs? Or can I pipe it easily somehow? Then I am buying little dirtbikes or sporty cars and will place them on the track. Thank you!

If you have the Wilton cake icer tip (the really flat, wide one) use that to pipe the track. It will be really quick. If not, then graham cracker crumbs would work well, too. I would put them in a funnel so that you can control exactly where they go on the cake - maybe pipe borders and then funnel the crumbs inside that.