What engine do you have on your trainer that went bad? Remember that no engine will hold up very long to constant lean running. As far as which engine is better between the SK and the Magnum, I would have to say that I really could not say. I have never owned a Magnum 2 stroke engine. I have owned several of there 4 strokes and have been very happy with them. I am so happy with the way my new SK .90 is running, that I went ahead and ordered another one just to have another one around. So I have been happy with both the Magnums I have had, and the SK. The important thing to remember no matter which engine you buy is tune them correctly, and do regular preventative maintence. I will say that the SK .50 will be the more powerful of the two, but if this is going on a trainer the Mag .46 would probally have plenty of power as well.