thanks! you see, I come froma huge toyota backround, with a dabble in nissan as well. in nissan, the numbers signify the displacement of the engine: L28= 2.8 litre inline six, vg30= 3.0 litre v-six, rb26= 2.6 litre inline six. whereas, toyota engines use the number to signify the generation/technological advancement of the engine: 7m= 7th generation m-series engine(inline six) fount in mk3 supras& in cressidas, 4ag= 4th gen. ag series engine, found in ae86 corolla, and in the 1st gen MR2. when you combine two engines, you use certain aspects of the coding of both engines, the best example of which I can think of is the 7a-gze. using the block of the 7a-fe in the newer celicas, the head off of a 4a-gze, out of a sc'd 1st gen. MR2, and a sc that would be used on aformentioned MR2. combine those factors, and you get the 7a-gze. By the way, in toyota, a "z" after the dash means its sc'd, a "t" means turbo. now if someone explain to me the method behind the numbers in subaru codes, it seems that some represent the displacement, but I dont know about the others.