When my uncle, a Chevy mechanic used to refer to our ol' stovebolts he just called it a "6". Everyone knew what that was, all the way up until the 80's a Chevy 6 only meant one thing, an inline 6-cylinder motor. Then, when the V-6's came along (I know about the early GMC's) I guess there had to be some way of differentiating between the two so it was called the I6. I just assumed that meant an Inline 6. Now, I see people reffering to them as L6. Where does that come from, and what does it mean?
