Charles,


With the Pitts, muffler and a big prop, the MVVS .91 has a definite advantage in power.
On the other hand it is more expensive.

The best power system for the .91 is to mate it with the full length tuned pipe #3250.

The .77 responds very well to the shorter, lighter mini-pipe #3253.

Contact David Moen, representing MVVS in your country.
You can find him here and I remember he is actually flying with such an engine.