So you've done the heads and cam swap and added all the bolt-ons your late-model LS-powered Trans Am or GTO can stand, but 11-second time slips are just not scratching the itch anymore, and you're ready to step up the excitement level. Perhaps it's even time to retire your Pontiac from daily transportation duties and snuggle up to around 500 cubic inches and a big dose of power adder. Until recently, this would have required tossing your modern LS-series engine and converting to a Pontiac IA II based engine, or commiting the sacrilege of swapping in a big-block Chevy, but no more. The impressive efficiency of the 15-degree LSX series heads can now be used on a block that can deliver serious inches, rock-like stability, and 6-bolt head clamping-all for about $2,000!
The Current Choices
The LS family of engines has already come to be regarded as great street performers, and the number of companies offering speed parts and power-increasing services for them has grown tremendously. Unfortunately, the lightweight aluminum block that helps them to be so potent on the street eventually becomes an Achilles heel when we talk about serious drag racing, and single-digit e.t. cars with LS OEM blocks are viewed by some as hand grenades with the pin pulled.
Some racers go with sleeved LS2 blocks, but apart from the '05-'06 GTO, no Pontiacs have come with LS2s. You must figure in the purchase price of the OEM block with the cost of sleeving it, which increases the cash outlay to more than buying the LSX block outright.
Another option is the C5-R block. CAD designed for prototype road racing as part of the chassis, it was never intended for public sale, let alone drag racing, so it is very expensive and simply does not allow the overbore size and stability of the LSX iron block.
World Products has announced its Warhawk block, a 356-T6 aluminum piece with iron liners. It appears to be sturdy and has many features in common with the LSX block, such as 6-bolt heads, priority oiling and provisions for a dry sump system, but it will have a smaller bore capacity and is over twice the cost of an LSX block.
The General Motors 6.0 liter iron truck block is the value leader. Although overbore capacity is limited, it is reasonably sturdy, cheap and can be stroked to about 410 ci. However, it was never designed as a performance block and was replaced in the GM trucks with an aluminum one in '07.
What is needed is a block that can be safely bored to 4.250 without getting major cylinder wall deflection, and it must have a rigid, thick deck with extra head bolts to hold the cylinder pressures required to reach over 2,000 hp. The real dream is to be able to do this at an affordable price. GM Performance Parts has now stepped up to the plate with a big bat, but will it be a home run?
Inside The Lsx Block
The new GMPP LSX block is not simply a thicker version of a production block. Instead, it was designed from a clean sheet of paper with the help of famed Pro Stock racer Warren "The Professor" Johnson specifically to withstand racing stresses. GMPP reps estimate that it will handle 2,000 horsepower. Essential to achieving this goal was a very rigid structure for minimum cylinder deflection, increased crankcase web strength and head sealing, yet it still had to allow the largest possible bore-up to a 4.250-inch-while retaining 0.200-inch wall thickness. This required the inherent strength of a Siamesed bore iron block.
Although the LSX block pays a weight penalty because of the beefy construction and material choice, it is simply because "The Professor" kept nudging GMPP to design this block with no compromises in strength or limits regarding the ability to fit true racing components. This makes it perfect for use in high-boost/large displacement racing and extreme street car applications.
GM chose an extra-tough 280 kPa tensile strength block material (stock iron castings are 220-240, anything above 280 makes machining difficult), which not only helps rigidity but will also aid in bore durability. Features include 1045 billet steel 6-bolt main caps, two extra head bolts per cylinder (now six per hole), much thicker Siamesed cylinder walls and other beefy areas throughout to allow maximum head clamping integrity as well as distortion and twist resistance.
Another benefit of this sturdy construction is that the significantly thicker areas around the cam bearings and lifter bosses were designed to allow machining for oversized lifters and larger cam bearings to support the huge race cams that a serious racer will need to be competitive.
Other design characteristics of interest are extra bay-to-bay breathing pockets, which GM engineers found critical to high rpm power on big engines, and drilled and tapped bosses on the block for mounting motor plates. The oiling system on this block is a true priority system. Oil from the pump exits the filter, goes directly to the main bearings, then is routed to the cam bearings and valvetrain. This is beneficial because it puts the freshest, coolest oil at the main bearings with minimum startup time, minimizes pressure fluctuations at the mains, and tends to reduce windage by requiring less oil to be returned from the top end to the sump. If you're going to go racing with an LS-family engine, this is the block for you
Because the new LSX block was designed to use as many components as is practical in going back to the LS1, all LS-engine-equipped cars will find it easy to convert to a big displacement or high-boost racing class simply by adding the LSX block to their engine build recipe.
Only two caveats prevent transferring all of your existing hardware from another LS-family engine-the first being the need for special lifter retainers to get to the sixth head bolt access windows in the block valley. GMPP includes the required lifter retainers with every block, even though they are only needed if the engine builder decides to use stock-type hydraulic roller lifters. GMPP designed the extra head bolts to use studs that thread into the bottom of the cylinder heads, as running bolts in from the top would require compromising the head and intake port areas with holes to allow bolt access from the top. With the stud design, nuts can be easily put on the extra top head bolts from the intake valley windows and on the bottom bolts from outside the block. If your engine doesn't see very high cylinder pressures, feel free to use the standard pattern to bolt up whatever LS-type heads you want with the standard 4-bolts per cylinder.
The LSX block incorporates many drag racing specific features, but is also designed to be fully compatible with street-driver needs. | 
This OEM GM 6.0 Liter truck block was disassembled and photographed for comparison with the LSX. GM replaced this iron block with an aluminum one in the Escalade and trucks in '07. Overbore capacity is limited compared to the LSX, but the price is very reasonable. | 
The LSX block, when compared to the 6.0L iron block, shows the extra head bolt provisions (top and bottom of bores) and the cam valley windows that access the end of the top head bolts. |