Steve:

Have you considered the OS R5-300? It's about the same six inch diameter of the A7 and B5 Technopower, and a lot more powerful.

Or for less money and even more power the ASP five cylinder radial is a full 4.0 cid, one third larger displacement than the OS. If you have room that one would do very well.

I just wanted more than five cylinders showing, so that meant the Technopower A7. Granted, it's only 1.35 cid, but my f7f issmall enough to fly with 0.40 two strokes, so my only problem will be trying to make up for the weight.

Bill.