If you're setting up a track for 1/8th scale I HIGHLY recommend doing exactly what Bob said. Use two 2x4's stacked with ends rounded (all you really have to do is cut off the corners...like the pic.) We don't have a lot of nitro cars racing with us lately, but when we had, the really serious wrecks would sometimes cause the board to split where the bolt goes through the lap joints.
We thought about the stacking of 2x4's for our track. The biggest reason we decided against it because it does double the weight being hauled around and we were not sure if our trailer was going to be able to handle it, the drivers stands, the outer boards, timing tower, pop-up tents, several tables, etc....
rD Squared-MW Designs-C and R racing
Final Thoughts RC club R.I.P.