I agree that the Magnum 91 as a great choice for the Hog Bipe. I was in the same boat as you not wanting to spend a fortune for a 4 stroke, but the Magnum was affordable and is a great performer. I initially flew the Hog with a .75 2-stroke and it flew with authority. I decided to try out the 4-stroke after several recommendations and the 91 4-stroke/Hog Bipe combo is hard to beat. Best of luck with your build!