With more than 2,000 horsepower put to the pavement, Mark Koehler's drag radial Trans Am blew through the 2010 racing season with a best e.t. of 7.50 at 194 mph. The combination that generated that performance was a Kurt Urban-built 440-inch engine with the typical forged internals, a hydraulic roller cam, and a big, 106mm single turbo. And unless you're a regular in the pits at the LSX Shootout and other drag radial competitions, you may be surprised to learn the foundation for Koehler's engine isn't one of the dedicated racing blocks on the market, but a production 6.0-liter LS2 block-albeit one with some pretty serious reinforcements from ERL Performance.
"It's been a remarkably solid engine and through an entire season of racing, we didn't have any bottom end issues," says Koehler, a member of that group of turbocharged, envelope pushers known as the Ohio Boys. "Kurt [Urban] did a great job building and tuning the engine, but that ERL Superdeck block really held up to all the boost."
Before we get into how ERL modifies the block and the materials they use, lets get to the root of the issue: Why production blocks fail in extreme high-performance combinations. In the most basic terms, they weren't designed to be used as 1,000-, 1,500- and 2,000-horsepower racing engines. More specifically, they weren't designed to support the cylinder pressures those engines experience, especially under high boost. An LS1 engine, for example, has combustion pressure of about 1,100 psi, although a high-boost engine producing more than 1,300 horsepower and 1,400 lb-ft of torque will generate about three times that pressure: 3,000 psi. In regular-production aluminum LS1 engines, it's the cast iron cylinder liners that take the brunt of the abuse. They crack. It's a similar story for other production LS engines. Even the iron (truck) blocks, which have long since been popular among power-adder engine builders, just aren't designed for that level of stress.
"All things considered, GM did a really good job in the design of the LS engine, but it was designed for passenger vehicles, not 1,500-horsepower True Street cars," said ERL's Sean Ragains. "If the tune is on the ragged edge or the boost pressure is really high, it doesn't take much to break the liners, decks, or the block itself."
A dedicated racing block, such as the LSX, RHS or Warhawk, provides the added strength necessary to support the cylinder pressures of a high-power engine, but ERL has done a remarkable job building exceptional strength into production engine blocks. It's accomplished primarily by installing the Superdeck I system, which includes aluminum trusses to strengthen the block and ductile iron sleeves to withstand the combustion pressure. It may seem contrary to what seems necessary in a high-pressure engine, but ductile iron-which is infused with nodular graphite-is surprisingly elastic, which makes it extremely durable. The graphite nodules used in the material are spherical, which inhibits the formation of cracks. In fact, the name ductile iron is derived from its exceptional ductility, or its capacity to deform without fracturing.
"Ductile iron is three times stronger than the cast iron used in production LS engine block cylinder liners," said Ragains. "The sleeves we use have yield strength of about 110,000 psi, so they'll stand up to just about any amount of boost you can throw at them."
It is important to note, that citation of yield strength is different from the cylinder pressure load described above. The yield strength is basically the amount of stress the liner endures physically, which varies along its length. Finite analysis testing conducted by ERL showed that on the same 1,300-horsepower boosted engine, stress ranged from about 600 psi to about 12,000 psi, but the area directly under the "T-head"-the portion of the liner directly beneath the lip that seats it in the block-is subject to anywhere from 30,000 psi to 60,000 psi of stress. That's definitely beyond the range of the stock cast iron liners, but well within the range of ductile iron's strength.
"With three times the tensile strength of cast iron, there are advantages even when you're not running a power adder," said Ragains. "We've seen liners crack even in 700-horsepower naturally aspirated engines that were bored too large. Also, working with ductile iron not only gives us great strength, it enables displacement options, because we can offer liners that are thinner than stock." Perhaps more importantly, however, is the fact that the ERL liners, at 5.800 inches in length, are longer than the stock, 5.455-inch-long LS2 liners. That ensures that enough of the piston skirt remains almost completely within the cylinder to prevent high oil consumption, even on a long, 4.125-inch stroke.
GMHTP recently paid a visit to ERL's facility to get a look at the modification and machining process involved in strengthening the LS block into a big boost-capable foundation. In fact, there are a number of processes and options, with all of the basic re-sleeving packages featuring "dry" sleeves-a process in which the original liners are removed and replaced within the block's cylinder bores. That's different from "wet" sleeve systems that bore out the original cylinder bores so that the new liners are directly exposed to the coolant circulating around the cylinders. For a number of reasons, ERL mostly stays away from sleeving the early 5.7L LS1 blocks. "There are some design elements, such as thin casting support around the sleeves, that make them impossible to sleeve," said Ragains. "The LS2, LS3, LS6, and LS7 blocks are much better to start with if you're building an engine from scratch. We've also had good luck with the 5.3L blocks-and those without the crankcase windows have proven to be very good for turbo engines."
ERL offers a more basic dry-sleeve package, as well as a tall-deck Superdeck II system, with ductile iron liners and options like ARP head studs, billet main caps, a main stud girdle, and bronze lifter bushings. However, ERL says at 800 horsepower it is time to step up to the Superdeck I system. The four-bolt version is suitable for engines up to about 1,100 horsepower, with a six-bolts-per cylinder upgrade to support about 1,500 horsepower, but racers like Koehler and Brown are getting more than 2,000 horses out of it (with additional top-secret modifications). The big difference between the basic dry sleeve package and the Superdeck I is a unique truss design that connects each pair of factory head bolts with an aluminum bridge. It allows stress to be shared across the deck surface to minimize deflection and eliminate cracking where the cylinder attaches to the deck. Importantly, the Superdeck I design doesn't restrict water access to the deck surface in order to bolster head gasket retention. In fact, holes drilled in the trusses enhance upper-cylinder cooling, which helps stave off detonation that could be caused by a potential hot spot near the combustion chamber.
ERL points out the trusses tie together the main saddles in the block to the deck, too, which significantly increases the strength of the main saddles because the load path is altered. The six-bolt Superdeck I adds additional cylinder head bolts compatible with GM Performance Parts' LSX six-bolt heads, as well as other popular heads from All Pro and Trick Flow. Bores of up to 4.200 inches are available with the Superdeck I. Billet main caps and 1/2-inch ARP head studs are included, while a main stud girdle is a $500 upgrade. Of course, the topic of optional upgrades begs the question about the cost for these upgraded blocks in the first place. The basic dry sleeve package starts at $1,550, plus an $800 refundable core charge. All the extras, including the stud girdle, billet main caps, main studs, ARP head studs, and bronze lifter bushings, will add another $2,170 to the bottom line. The Superdeck I starts at $2,600 for the four-bolt version and $3,000 for the six-bolt version, with the girdle, head bolt and lifter bushing options pushing the price to just north of $4,000 (fully machined).
At this point, some will argue the case for the various aftermarket blocks out there such as the LSX block that costs less than $2,000. However, when you consider the cost for machining and the approximate 125-pound weight penalty over an aluminum block, it becomes much less cut and dry. Similar statements could be made about the others out there, and ultimately it will come down to personal preference. The one thing not up for debate, though, is that purchasing any upgrade to the factory block is a wise investment. Given that the added cost of a Superdeck I would amount to only 15 or 20 percent of your typical engine and power adder combination, the assurance and longevity of a reinforced block seems like a no-brainer. Heck, you can't do a bolt-on blower on a stock engine for less than about $7,500 these days, so even the basic dry sleeve upgrade seems reasonably priced. All things considered, the ERL Superdeck I is great insurance against the potentially expensive consequence of high cylinder pressure.