The horsepower ratings that marketers placed on engines only enable certain bragging rights to the seller and mean almost nothing in real practical use on a model airplane. If you'll notice, the rpm's given are usually way beyond any possible use. The reason for the difference between the two engines is that the Hobbico and Tower 46 are rated at 16000 rpm whereby the GMS 47 is rated at 15000 rpm.

The Magnum XLS 52 has a blue head very much like the Hobbico but the ports in the sleeve on this Magnum are placed half way between being a side exhaust and a rear exhaust engine. The exhaust stack sticks out in the pure side exhaust fashion though.

Enjoy,

Jim