I ran a FP 40 on my first Morris Knife a few years back. Of course with the stock muffler it was a real dog, just enough power to fly the plane around but without much authority. Then I found out about MCM pipes (mousse can muffler). I bought a macs header, found a site with a diagram for making a mcm and a few days later I was ready to try it out. %10 Omega (morgan fuels) 10-5 apc, os a-3 plug, cut about 1 inch off the lenght of the header. Fired it up, right away I noticed a different sound to the engine, quite pleasant really. Much more responsive throttle, and a noticeable gain in top rpm. I tached it, I had gained 1300 rpm over the stock muffler, with the same prop/fuel ect!! Needless to say the Knife was a real blast to fly after that. Plenty enough power to hover the plane, and it could climb out at a very good rate.
I ran this combo for a good year + 1/2 with no trouble. But I did notice the engine didnt run quite as nice as when it was new....of course. It still had the power and throttle responce but the idle wasnt as steady/smooth and it was not as user friendly to hand start, especially when hot.
So yes, the fp 40 does respond to a mcm pipe, and I would imagine it would gain good rpm on a tuned pipe as well. But be aware that all the extra rpm gained will wear the engine faster than running the stock muffler. I dont know what your running the engine on, but either a fun fly or a speedster, you might want to consider a mcm pipe, theyre cheap to build.

good luck