The start of any high-performance LS engine build usually starts with a choice between an iron or aluminum foundation.
Conventionally, iron blocks have been the favorite for big boost, four-figure horsepower engines used in straight-line spaces. This is mostly due to iron’s superior strength and its ability to resist flexing or distorting under high cylinder pressures. It’s also cheap. Meanwhile, lighter aluminum blocks often find favor in high-RPM naturally aspirated road racing applications or mildly boosted builds where the engine isn’t living on a knife-edge. Not counting billet blocks, of course.
LSR Block From Concept Performance
Enter Concept Performance and its all-aluminum LSR block. The company exploded onto the scene a few years back with the first-gen LSR, but its parent company, Ewing Light Metals, has long been serving go-fast-geeks as a private label manufacturer for several big-name brands. The aftermarket LSR block takes the design advancements of Chevrolet’s venerable LSX race block and offers it in a much lighter cast-aluminum package.
The LSR block is cast at the company’s foundry in Indianapolis, Indiana, from A356 T6 aluminum ingot and features spun ductile iron sleeves from Ohio-based PowerBore Cylinder Sleeves. The LSR is available with a standard deck height of 9.240 inches, or an optional 9.720-inch-tall deck. Both decks have a thickness of .750-inches. The tall-deck version offers a raised cam option and the cam bores of either deck height can be machined to accept 60mm roller bearings.
Most of these blocks are ending up in Corvettes, Late Model Engines (LME) is our largest LS customer and they’re working mostly with Corvettes. – Carlos Inocencio
“This block has now been out for about four or five years and we’ve gone through several generations starting with an LSX-style version that had almost no extra beefing up,” says company principal Carlos Inocencio. “Originally, the LSR was literally a replication of an LSX. Now the current version of our block is almost like a Gen-V block in terms of strength.”
When Chevrolet launched the iron LSX block in 2006 its bones were derived from the production design of the aluminum LS7 developed for the C6 Corvette Z06. Geared towards heavy-duty competitive use, design changes were made to increase the block’s strength and reliability when spinning at high RPM and swallowing big boost. Priority main oiling was added, along with six-bolt cylinder heads, thicker exterior walls, and copious cross-bracing throughout. Concept Performance continues to use many of Chevy’s original improvements, plus several more developed in-house over the years.
“The LSR has significant bracing through the valley. It has triple bracing through the sides of the block, the skirt is super thick, it’s 5/8-inch-thick in most areas of the skirt. The windage area under the crank saddle has been removed which creates a stronger brace between the saddle and the block skirt wall.”
Compared to a Chevrolet Performance LSX block, the LSR offers weight savings of more than 100 pounds. Even with the additional bracing and material thickness, the LSR block tips the scale at a scant 113 pounds, which is roughly the same weight as a production LS7 block. “We also now machine a radius in the crank saddle which attaches to the skirt wall, adding strength. There used to be a sharp corner where the saddle met the skirt wall. Any place you have a sharp corner is a breaking point, so this helps with strength. Blocks like the RHS or LSX have a windage window under the crank saddle that goes straight through the casting, we remove that so it’s solid through there now. This creates a stronger crank saddle,” explains Inocencio.
This is a significant improvement considering factory aluminum LS blocks can let go at the saddles when horsepower gets into four-figure territory. Properly built LSR-based engines are more than capable of handling 1,500 horsepower, while some in the wild are happily pumping out more than 2,000 horsepower.
The main caps on the LSR are made from billet 1045 steel and include ARP hardware. According to Inocencio, the cap design has evolved over the years to help with harmonics. The mains are offered in either six- or eight-bolt configurations adding to the overall strength of the package. As a result, the double cross-bolt option has a 40-percent larger main cap surface.
Moving up into the valley, the lifter bores can be enlarged to accept a larger bore or key-way style lifter. “The lifters start off as standard size but we can go up all the way to a .904-inch lifter bushing,” says Inocencio. “The valley is also cross-braced. We use PowerBore sleeves We suggest they can be bored to 4.185 inches max. All of the sleeves we use are the extended version.”
The final machining of the LSR is done at the retail level by Concept Performance’s cadre of dealers. Some dealers claim cylinder bores can range from 4.065 inches all the way up to 4.200 inches depending on your final spec, this helps facilitate a wide spectrum of bore-stroke ratios. The raised-cam, tall-deck version of the LSR can take up to a 4.600-inch stroke.
“Our decks on the LSR block are 3/4-inch minimum thickness after machining, and also include a cam thrust plate and rear cover. The cam bearings are included for the engine builder to install.”
Like the iron LSX block, the aluminum LSR will accept six-bolt cylinder heads — the greater clamping force becomes mandatory with increased cylinder pressures from big boost. However, the block will happily work with production-based four-bolt cylinder heads for milder applications. The block also has a seventh transmission bolt hole in the rear of the block, facilitating the use of older GM transmissions like the Powerglide.
In just a few short years the LSR block has established itself as a capable performer and popular choice for those looking to blend the strength of an iron block with the weight advantage of an aluminum block. “Most of these blocks are ending up in Corvettes. Late Model Engines (LME) is our largest LS customer and they’re working mostly with Corvettes,” adds Inocencio. From a cost standpoint, the LSR is quite competitive with Chevy’s own catalog blocks, and considering the LS7 and LS427 are being phased out of existence, that’s a very good thing.