Good luck with that "trouble maker"

The exhaust parts are used from other existing engines.....

The engine uses the muffler for the OS 91 Surpass II engine

http://www2.towerhobbies.com/cgi-bin...?&I=LXCP62&P=Z

The exhaust pipe is the one for the OS FL 70 four stroke.

http://www2.towerhobbies.com/cgi-bin...?&I=LXKXY9&P=Z

The thread size for the exhaust is M-11 X .75

Four strokes are not as sensitive with respect to the exhaust as two strokes are.

You can use any exhaust/manifold - muffler set up that has the correct 11mm diameter X .75mm pitch on the threads.