Supercharged LSX Engine - Poor Man's LS9

Right off the bat, let's be clear about this story's title. "Poor Man's LS9" can be interpreted many ways, because wealth is a relative term. So, with the new ZR1 stickering for $103,300 (plus dealer markup), a more appropriate-albeit less catchy-title might be "Less-Affluent Man's LS9" or "Engine for the Man Who Didn't Get on the ZR1 Wait List."

Nevertheless, what we've got here is a 427-inch engine combination that is based on GM Performance Parts' LSX cylinder block and approaches power in the same supercharged manner as the LS9, but exceeds that engine's factory-rated output. And while this mill could never be considered inexpensive, it's well within the realm of attainability for enthusiasts with the means.

The foundation for the LS9-challenging engine is GM Performance Parts' LSX block. It comes semifinished with 3.99-inch bores that were taken out to 4.125 inches for this application. The LSX also features provisions for additional cylinder-head bolts, and it accepts just about any component from the LS engine family.

This supercharged LSX is the brainchild of Brian Thomson, who runs Thomson Automotive in the industrial suburbs of Detroit. He works closely with General Motors on a variety of engine-building and dyno-testing projects, and he has about as much experience with high-power LS engines as anyone in the business. Like Tim Robbins' character in Bull Durham, Thomson envisioned the engine as a way to "announce his presence with authority" when it came to LS performance.

"Cars with 500 and 600 hp are as common as pennies," Thomson says. "We wanted to build something with basically off-the-shelf parts that pushed the 800hp barrier."

It helped, too, that Thomson had access to some of the first examples of the LSX cylinder block-the cast-iron engine foundation that was developed with assistance from legendary drag racer Warren Johnson. Because of the LSX's purported capacity to support tremendous boost, Thomson figured it was the safe bet for ensuring a scatter-free first pull on his engine dyno. Even better, it was about one-sixth the price of a C5-R block. (LS7 blocks were not readily available when the project started.)

The LSX block is made of cast iron, making it more affordable than a comparable aluminum unit. A 9.26-inch semifinished deck height is standard, but we expect a tall-deck version to arrive any day now. Like other LS blocks, the LSX uses a long-skirt design and six-bolt main bearings.

"The LSX is a really strong block," Thomson says. "Our experience suggested it would handle the power we were looking for without a problem, whereas we would have been pushing the limit on a C5-R block."

Putting the pressure on the LSX block is a new Eaton-built supercharger from Australia's Harrop Engineering. As Roots-type blowers go, it's a monster, displacing 2,300 cc (the same as the one on the LS9) and capable of more than 20 pounds of boost. Thomson figured he'd need at least 15 pounds to reach his 800hp goal.

But while the blower is not yet widely available in the United States (Harrop's U.S. arm says it will be soon), the rest of the combination is a straightforward design built with off-the-shelf components. That's not to say this was a budget build, but there's nothing here that couldn't be easily duplicated.

"The parts in this engine are either already available or will be soon," Thomson says. "That's a key part of this project: It's awesome power that is available to anyone who wants it."

On this engine, the bores were finished with torque plates installed to ensure accuracy and promote head sealing.

The crankshaft is a stock LS7 forged-steel piece providing a 4.000-inch stroke.

Forged rods from Oliver were also used. They have an I-beam configuration, which enhances strength.