Hi there!

Manufacturer's horsepower ratings are as good as meaningless to you. Ignore them. Choose your engine based on the engine's size class, cost, weight and the manufacturer's reputation for reliability and service.

You're looking at large 40 class engines. Many manufacturers will design a basic .40 size engine, and then offer basically bored out versions at .45 and .51 or even up to .55. They're all based on the same case, and often the same crank, so the larger displacement engines will often be both lighter and more powerful. Judge the engine's power by looking at the props that people swing with them. A .40 will typically use a 10x6 prop, while a .45 will use an 11x6 prop and achieve similar RPM's.

Look at the rated RPM's where they give the hp numbers. Over 15K rpms! When we choose a prop for a sport engine (anything non-competition, generally), we choose one that will put the engine in the 10K-13K rpm range for good life and good power. That horsepower rating is similar to if Honda were to rate your civic's engine at 300hp at 10Krpm. Great, but who's gonna turn it that fast, and how long would it last? No-one. Not long.

If you're looking at specific engines, ask about the specific engines. Problem there is, it's often a "ford/chevy" debate. Most of the well known engine manufacturers (OS, Saito, Tower, GMS, Supertigre, Thundertiger, Magnum etc, etc) make good engines. Some have particular quirks, and people here know them to have them. They'll let you know, and suggest options if you've chosen one they wouldnt' recommend.

Also it would be helpful to know what plane you want this on NOW! There are lots of great 40 size sport planes you can move to later, but match the engine to the plane you HAVE.

For what it's worth, I've played recently with the OS46AX, the Supertiger G45 and the Evo trainer engine. The OS was easiest to tune and break in, the Supertiger was harder to break in, and slightly harder to tune, the evo was a breeze to break in but finnicky to tune. The Supertiger and the OS put up nearly identical RPM's on the 11x6 (about 13,100-13,300), and the evo was behind a bit (about 12500). The OS has been most reliable in teh air, but all have been pretty damned good!

J