If you go to Ed Hartley's page, you can see a lot of different OS1.40 set ups. http://www.rcpattern.com/2cycle.htm

I used a pipe for a while, but the last two planes I have used a Bolly 590 muffler. No set up or tuning with a muffler. Mine turns a 15,5X12 4 blade at over 7,800 rpm on 15% fuel. Plenty good for most 2M's. I'm half convinced that by the time you make a tuned pipe long enough not to have a noticeable"peak" that you lose much of the benefit of a tuned pipe.