if you are speaking of the SPA. The motor of choice in our group seems to be the OS 91 FS. Very reliable. Its in about 90-95% of the SPA aircraft at a meet. I am installing one in an ALtair for SPA.
Also have one in a Daddy Rabbit that I compete with now.
The Altair is a huge plane as far as SPA planes go, it will be weighing in at about 7.5 lbs i think. Check it out at my webpage . The webpage is fairly new, and lacks much content. But the Plane constuction of the King Altair is full of photos. and some good photos of the Huntsville contest, we took photos of all the contestants .

gwair.com