whats the difference between

lt1-
lt4-
ls1-
ls6-

i dont know if i got the numbers right but whenever i see it i get confused

 

The LTx's vary from the LSx's in firing order, heads, building materials, bore and stroke, intake manifold,usuallysize (i.e. the LT1 is a 350 c.i., the LS1 is roughly a 350 c.i., but the LS7 is a 427 c.i.). The LT4 has a slightly different intake than the LT1 and a more aggressive cam as well as some slight tweaking done to the heads. The LSx's can vary amongst themselves with size and other things too.
They are all technically Chevrolet small blocks but they can be different enough that parts can't be interchanged amongst them. If you want to look up exact specs you can go to Wikipedia and lookup the LSx engine and the LTx engine and compare them.