The great thing about big-block Chevy engines is they offer gobs of luscious torque-producing displacement. The downside is that they are big and heavy, which has resulted in a trade-off between weight and displacement. These days, however, there are ways to have your proverbial cake and eat it, too.
The problem with going bigger, especially with today’s aluminum GM blocks, is that the factory steel sleeves can only be bored so far before getting too thin to be reliable. The solution is to knock out the factory sleeves and insert aftermarket sleeves that are able to go big, real big. Having the ability to go with a bore size up to 4.200 inches is a key part of getting big-block displacement from the LS2. The other half of the displacement equation, stroke, is addressed with the use of a longer stroke crank. These are readily available and a 4.125-inch stroke can be accommodated inside the typical GM LS block with a bit of finesse. The upshot of this is it’s now fairly easy to create a lightweight aluminum LS engine in the 454ci range.
This bump in available displacement equates to torque and as we all know torque, not horsepower, is the real star of the show. In addition, those extra cubes allow the use of a larger camshaft that would prove to be too raucous in an engine of more diminutive displacement.
For this build we decided to use a set of Darton MID sleeves to punch out the bore of a used LS block. The recipe also included a 4.125-inch K1 crank with standard length 6.125-inch K1 rods. When it came to selecting the camshaft we resisted the urge to slide in something too rowdy just to nail a sexy dyno figure. Instead, we chose a stick that would make great power and still offer excellent street manners. After getting our donor block resleeved by Steve Demirjian, of Race Engine Development, we headed over to Turn Key Engine Supply to complete the big-inch mill.
It’s bigger on the inside
Sleeving an LS block involves very specialized, and expensive, equipment, but more importantly it requires someone with the skill and experience to pull off the surgery. That’s where Steve Demirjian of Race Engine Development comes in. He’s been in the racing engine business since 1972 and that equates to a lot of knowledge of what works and what doesn’t. In regards to sleeves he’s been working with Darton for quite some time and is even one of the patent holders for their Modular Integrated Deck (MID) sleeve system. The MID system was developed by Darton to address the factory block’s cylinder stability design weakness due to the poor support at the upper deck area. GM’s "cast-in sleeves" make the factory engines affordable and they are great to a certain power level, but lacking when it comes to high power, boosted, or, as in our case, larger bore sizes. When the Darton sleeves are siamesed and nested, they create a solid deck of sleeve flanges held in tension, this reinforces the upper deck area and provides for individual replacement with what Darton calls MID. Unlike factory sleeves, water flows all the way around the cylinders and this promotes cooling and helps control detonation.
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.