Just some thoughts and random stuff to toss out:

- HP numbers, as reported by engine companeis is a totally useless number. They get the HP reading using a really small prop and cranking the engine to some serious RPM, much higher than you'd see in normal use. You really want to know the HP produced at the engine's peak torque RPM, but no one reports that. So, to know what engine is more powerful, you need to actually look at tach readings for the prop you want to use and compare that way.

- Due to differnet port timings and bore/stroke ratios, etc, some engines like to run at high rpms with small props, others like to turn slower with larger props. This means that the HP numbers might be totally misleading, since a trainer usually flys better on a slower turning, larger prop. An engine that is timed to scream on a small prop may not fly the trainer as well as one that produces more low end torque.

- The good news is that most of the common engines you see mentioned here are built for generally good running at moderate RPM, using fairly conservitive port timings and compression ratios to make the engine easy to tune and put out decent power in the process.

- Ringed engines, in theory, last longer than ABC engines. However, most engines are done in before they are just worn out, so really, life span is determined more by how often you fill the engine full of dirt than anything. Not all piston rings are Dykes rings, but many (most?) are. I have seen worn out engines though.

- On a ringed engine, you can replace just the ring. On ABC engines, the piston and liner are a matched set and have to be replaced together. It should come as no surprise that the piston/liner combo is the most expensive part in an ABC engine. So, if you eat dirt and kill your compression on an ABC engine, the repair is going to cost you. Ringed engines tolerate dusty envrionments better, and can sometimes survive eating stuff that would kill and ABC engine.

- On the flip side, as a ringed engine heats up, the ring expands, creating a better seal. If the engine overheats, the ring can seize in the liner. The result is a dead engine. I've seen ringed engines break conrods and crankshafts just because they were set a little lean and overheated. Since you also have to replace the piston and liner when that happens, you have an instant paperweight.

- As ABC engines heat up, the liner expands faster than the piston, so the hotter they get, the looser they are. So an ABC engine won't be harmed by over heating, it just looses compression and slows down. Note, however, that a lean run is the most common form of overheating. If you run lean, you can still damage the engine due to lack of lubrication. But the engine won't seize up like a ringed engine will. And if you over heat due to a bad cowl install, you probibly won't hurt the engine.

- ABC/ABN is just one kind of non-ringed engine. There are a few other types out there. Norvell, for example, makes some interesting non-ringed engines. However, ABC/ABN are the most common engines in the .40-size class. ABC Stands for Aluminum, Brass, Chrome. Al Piston in a Chromed Brass Liner. ABN is the same, but Nickle instead of Chrome. OS has something they call ABL. It's really another flavor of ABN, they just claim better Nickle alloys.

- BB engines are heavier, and as said, usually produce more power than bushed engines in the same size, but not always. Norvell, for example, makes some bushed engines in the .25 class that absolutly kick but and will out rev most BB engines and weigh a lot less. (but they have a reputation for being touchy.)

- FSR used to mean Shnerle (sp) ported. Most all .40 class engines are ported this way now. This porting is basically a way to get more fuel/air mixture in to the engine and get more power.

- .46 engines came about by taking .40 engines and boring them out. (In fact, some .40's can be converted to .46's by just replacing the pison, liner, and head. The case, crank, bearings, carb, etc are all the same). So they usually weigh less than a .40 and produce more power. Many .50 size engines are also bored/stroked .40's so they fit the same mounting dimenions. .40 size engines are slowly going the way of the Dodo, there is no reason to buy a .40 when a .46 is available for $5-$10 more from the same company.

- That said, a .40 as part of a combo deal that meets your budget isn't necessarily a bad idea. I have an OS .40 LA I run in a beater trainer. It's not as powerful as some engines, but with the baffle removed from the muffler and an APC 10x5 prop, it pulls the trainer around well enough.