Okay this is killing me. I'm a newbie here, and a fairly inexperienced newbie when it comes to performance street engines (was involved in circle track racing for a few years, but that's really a different game all together). Anyway, regarding the Gen-I versus Gen-II SBC blocks, I keep finding conflicting information.

Specifically, I cannot figure out exactly what to call the blocks used between 1987 and 1992. I know that the pre-'87 blocks were Gen-I 2-piece rear main seal blocks, and the blocks used in the '92 LT1 and later (until LS1) were Gen-II 1-piece rear main seal blocks. But what about the blocks between those years?? I have seen them referred to as Gen-I blocks with 1-piece rear main seal, and also as regular Gen-II blocks. So which is it? And if they ARE actually a 1-piece rear main seal Gen-I block, then how are they different from the Gen-II?... and why did they not call it a Gen-II (making LT's Gen-III, LS's Gen-IV, etc.)???

Can someone clarify this (stupid) question for me PLEASE?! It's driving me nuts

Thanks y'all

 

The Gen 2 engine family is the LT-1's made between 92'-97'. The one peice rear main seal engines that are not LT-1's are still a Gen 1 family motor. The Gen 2 LT-1's have a slightly different block design for its cooling passages and a few other item's that are only used by the late model LT-1.

 

Gen 1.5, thats what I hear some people call them. Most of the parts that actually bolt to the block interchange, the main ones that dont are the rear seal retainer, crank(and flywheel/flexplate), oil pan, etc. Heads, accesories, transmissions, all will bolt up. Even though the serpentine accesories are different they will bolt up. I have never run into one that didnt have roller cam provisions either, even the ones that didnt actually have roller cams. The other main differences being the intake bolt pattern for the iron heads, but that doesnt affect the block, and the center bolt valve covers.

 

The 1990 Truck block I have is a '681' casting and its still a GEN I block. Nothing changed about it besides the 1 piece rear main.

 

i dunno where you are looking but i've seen tons of 1pc rear main blocks without roller cam provisions, up to and including 1992's. mainly truck blocks. i own several right now.

 

I have bought 3 different truck blocks for personal use, all 4 bolt mains, no roller cams, but they all had the provisions. And that is just what I got when I asked for late model truck blocks.