HalH,

I have not compared in actual tests but I went through this research in the past couple of years in selecting my combination.

It depends on the airframe that you will be installing the unit into. It is my impression that the OS 91/ Ramtec and Dynamax are very equivalent. The Dynamax may give a little better static thrust than the Ramtec I am told. The BVM combo tends to be highly regarded but very expensive.

I believe from my research and my application that the BVM would rank #1, Dynamax #2, and Ramtec #3 . I did not feel that the percentage of greater power that the BVM provided was affordable to my working budget. If it was, that is what I would be installing now instead of the Dynamax.

In any case, if the combination is not set up correctly with the inlet and outlet area configured for optimal thrust and attention to the airflow through the ductwork, you can really rob the efficiency of the system and wind up with poor performance.

Hope this helps,

Kaos1