a friend just purchased a alpha 60 arf whats the range of engine choices he has to simplify whats the biggest and whats the smallest he could install between the evolution and the os engines

OS Engines: .55 AX / .65 LA / .61 FX / .75 AX

Evolution: .61 NT

.75 ax wouldnt be too big?

It will phisically fit where any 60 size 2 stroke fits. Just more power. Also I did not include your freinds four stroke options if that is something he would be interested in.

A .46-size ball-bearing engine like the O.S. Max .46 AX or Evolution .46 NT would fly an Alpha .60 ARF trainer just fine. Extra power wouldn't hurt anything, however, and it might make the plane easier to fly in windy conditions. Engines get much thirstier as you move up from a .46 or .52 to a .61 or .75. A smaller engine would allow for longer flight times before having to land to refuel.

A two-stroke in the .52 to .61 range or a four-stroke in the .70 to .82 range would be a nice compromise between power and fuel economy. You might check out Ed Moorman's thread in the glow engines forum on the excellent JBA .56 2-stroke engine available from www.kangkeusa.com for just $79.99:

http://www.rcuniverse.com/forum/m_6762745/tm.htm

Ed compares the JBA .56 to the new O.S. Max .55 AX quite favorably, even though the JBA engine barely costs more than half the price of the O.S. model. Power, economy, and $70 extra dollars to spend on servos and a receiver; how can you go wrong?