Yes, the engines forum here on RCU!
The .40 .46 ect, is refering to cubic inches, ie-.46 being just shy of a half cubic inch. Not to confuse, but the numbers are fairly secondary. A good .32 can out power a crappy .46. So..... best to learn all you can, and a decent .40 size is a good engine to start with. The Evolution TPS is a good all around starter engine, reviewed here on RCU.

Jetts