We found an old LS2 block with scored cylinders, but Demirjian says various LS blocks would be suitable candidates. As he explained, "I like the LS1 block because it has solid main webs with no cast-in breather holes. I will install the large bore, 4.200-inch sleeves in the LS1 blocks but not the LS6. The LS6 blocks have the cast-in breather holes making them too weak, in my opinion, to bore out for the larger bore sleeves. Now the Gen IV blocks also have breather holes but on these blocks the floor of the coolant section has been raised leaving more material for the sleeves to sit on, resulting in less chance of cracks developing compared to the LS6 block." The process of installing sleeves is an exercise in supertight tolerances. Bore centers must be held to within +/- 0.0005 inch. The bores themselves, for sleeve fitment, must be held to +/- 0.00025 inch, or a quarter of a thousandth of an inch! This is why having the right tools and skills are imperative.Demirjian has had blocks come in from various shops doing the installs dry that were six thousandths out of spec. In these cases the block couldn’t be saved and the only option was to pull the sleeves and install them in a correctly machined block.
If all of this sounds labor intensive, that’s only because it is. The basic charge to machine, stress relieve, install the sleeves, and deck the block is $1,175. Add in $100 to bore the block to within honing range and another $75 if you want the notches cut for rod clearance. The sleeves retail right around $1,300 and when you add it all up, you’re at $2,650 for parts and labor. Of course, you have to factor in the cost of the block, but good used donors can be found for around $400 (give or take). That means the total for a big-bore aluminum small-block would be a hair over $3,000. Not cheap, but very competitive to the aftermarket LS blocks that are currently available.