What are all these different letters on engines stand for?[&:]

It's like auto manufacturers, i.e. Mercury Grand Marquis GS or LS etc. Sounds good. The FP is OS's older version of their bushing engines. Their newer versions are called LA. I have never heard of any specific meaning for the letters other than to designate families of engines.

I second that.
I was talking to a tech at hobby services (warranty dept for OS etc) I asked that very question he basicaly said almost word for word what Jim stated.

While the letters are not important, what IS important is whether the engine has a bushing or ball bearings. For instance, on the OS 40 FP and 40 LA, the crankshaft is supported by a bushing. On the more expensive engines, such as 40 FX or the new AX series, the crankshaft is supported by ball bearings. While these engines are a bit more expensive, they are considerably more powerful.

So MinnFlyer, is it the bearing setup or the difference in porting that accounts for the difference in power?

They may both contribute. I don't know for sure that the porting IS different. After all, if you found one type of porting that worked better than another, wouldn't you use that porting in all of your engines? I used to build Machines for the automation industry, and I can tell you first hand that the machines with bearings felt 10 times smoother than their bushed counterparts.

My bushed counterpart is the reason I cant afford the good engines !!!!LOL

ready to fly wed's, gitterdun.... you in ????

Not if the marketing department wants to sell a cheaper line of engines and you don't want them to siphon sales from the better line. Now, consider the Norvel Big Mig 25. Hard to tell the power difference from the bearing model. Also, look at the OS LA 15. It is a well known screamer often out performing the competitors bearing models. Please note that OS has no bearing model in the 15 size so they are not competing with themselves and are free to use aggressive porting without hurting their own sales.