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LS7 Unplugged

Here's an inside look at the biggest, baddest small-block ever built by GM

Jul 27, 2005

lthough it's built on the same Gen III/Gen IV architecture as the current LS1 and LS2 engines, the 7.0-liter LS7 that comes as standard equipment in the '06 Corvette Z06 can't really be compared with them.

No, the 427-cube, 500hp, all-aluminum power plant more closely matches up with the legendary big-blocks of the musclecar heyday. While speculation has raged for years regarding the actual output of Chevy's baddest big-blocks, the new LS7 now ranks right up there with them as one of the most powerful engines ever offered by Chevrolet. Did the 1970 LS6 really make just 450 hp? And what about the supposed 475 horses of the ZL1?

Chew on these stats for a moment:
*The bore is 4.125 inches and the stroke is 4.000 inches*CNC-ported aluminum heads have 12-degree valve angles--just like the American Le Mans racing Corvettes
*The intake valves and connecting rods are titanium
*The camshaft delivers 0.591-inch of lift and 230/211 degrees of duration at 0.050
*The dry-sump oiling system is connected to an 8-quart reservoir mounted in the engine compartment
*This is, after all, the engine of a street-legal production car, but a rollcage and a set of Comp T/A R-1 tires are all the car needs to be a full-fledged track competitor.

Just as interesting as the LS7's specifi-cations is its assembly process at the new GM Performance Build Center (PBC), in the industrial 'burbs of Detroit. A single technician builds each engine by hand. It's a process that marches 180 degrees away from GM's typical mass-production methods.

The V-8 plant at St. Catharines, Ontario, for example, will produce thousands of engines in a day; the PBC might build 100. Indeed, it's a more intimate procedure, with a small, hand-selected group of experienced enthusiasts performing the assembly duties.

We toured the facility recently to watch--and help with--the assembly of an LS7 engine. At 100,000 square feet (and not all of it currently utilized), the PBC's shop floor is downright miniscule compared to other GM large-scale manufacturing operations. While we've been through other GM plants, and were surprised by the cleanliness and brightness of the assembly area, the PBC ratchets those qualities up several notches. It's more like the setting of a high-end Indy car or NASCAR race shop.

You'll see the LS7's build process unfold in the accompanying photos, but here's a quick rundown of the overall assembly procedure: Each engine is hand-assembled by a single technician who builds it from start to finish. (There's even a plaque with the builder's name affixed to the engine after the final inspections are completed.) He or she starts with a bare, cleaned block and begins the build by installing bearings--just like you would on an at-home build.

Yes, there are some power tools involved, most notably computer-monitored torque "wrenches" that provide far more accuracy and repeatability than conventional handtools could offer in a production line setting, but all the procedures are performed by the technician. He or she taps each rod-and-piston assembly into its respective bore and installs each main bearing one at a time. There are 13 build stations in a U-shape line. The technician has approximately 23 minutes to complete the task(s) prescribed for said station. There is a guide at each station that directs the builder to the tasks, the order they're to be performed, and even the sequence in which the fasteners should be tightened. A bar code reader at each station acts as the electronic checklist, recording the tasks performed, as well as every, single fastener's torque reading.

During our time on the line, we also learned a few more tidbits about the LS7, like the fact that Mobil 1 synthetic oil is the only lube used in the assembly, from the cam, to bearings, to any other part that needs assembly lubrication. It's stored at each build station in ketchup bottles.

After each engine is assembled and inspected, it is pushed to a balance station where it runs briefly on natural gas during a two-step balancing procedure. From the balance station, the engines are shipped to Johnson Matthey Testing in Taylor, Michigan, where they're subjected to a 20-minute "hot" test--10 minutes of no-load "break in" and 10 minutes of loaded operation. After this, the engines come back to the PBC and are ready to ship to the Corvette assembly facility in Bowling Green, Kentucky.

Frankly, we were amazed at the process because it seems so, well, un-GM. It's encouraging that even the General and his enormous mass production army can adjust the standard operating procedure when needed.

GM has suffered in the market and media this year, but the Z06 and, particularly, its hand-built LS7 engine, are examples of things gone right. Really right.


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The assembly process begins with a bare LS7 block, which is cleaned and washed in a several-step process to remove sediment or other debris. It's a completely different block casting than the LS2-type Gen IV block, with larger bores and a shortened height. There also is a prominent "7.0" identifier cast in one side. LS7 blocks are cast in Mexico, with machine work taking place in Canada and Ohio.

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The aluminum block is fitting with steel cylinder sleeves to accommodate the large, 4.125-inch bores. In person, the holes look big enough that Maxwell House cans might rattle around in them.

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The LS7's block and reciprocating assembly are compressed to accommodate the Corvette's fast hood line and taller cylinder heads, so the LS7's block is a little shorter than the 4.000-inch stroke would suggest. To compensate, each cylinder liner has small extension tabs to keep the pistons lined up the bores.

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The blocks are delivered to the Performance Build Center with the main caps installed, because the blocks are machined with them in place and the engine fitted with a torque plate. So, the caps must be removed before the crankshaft is installed. Note the painted arrows--the technicians paint arrows and inspection daubs everywhere on the engine. This will certainly cause restorers fits in 20 or 30 years.

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Specific to the LS7, the camshaft is a hydraulic roller with an astounding 0.591-inch lift (15 mm) on both the intake and exhaust sides and 230/231 duration specs at 0.050. Note the Mobil 1-filled ketchup bottle; the synthetic oil is the only lube used during the entire assembly.

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The camshaft slips in as one of the first assembly duties. The nifty handle makes the job a little easier. A temporary holder is attached at the rear of the block to prevent the cam from slipping out the back.

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With the cam and its thrust plate installed, the crankshaft comes next. It's a forged-steel, cross-drilled piece that provides the long 4-inch stroke. The geared ring on the rear of the crank is for engine timing. A crankshaft position sensor (CPS) tells the computer the exact position of the crank by counting the gear's teeth. There are 58 teeth on the gear (hence it's 58X name), but they are spaced for 60--one tooth for every degree of rotation. The two-tooth gap is what the CPS reads to know exactly where the crankshaft is on its rotation.

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The rods, pistons, and rings are delivered for installation as pre-assembled units. The rods are forged titanium and, because the titanium material is just about impossible to break, the rods do not have the production industry-common "cracked" rod caps. The rods are held on to the pistons with full-floating pins.The rods, pistons, and rings are delivered for installation as pre-assembled units. The rods are forged titanium and, because the titanium material is just about impossible to break, the rods do not have the production industry-common "cracked" rod caps. The rods are held on to the pistons with full-floating pins.

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Big valve cutouts on the pistons are an obvious difference from, say, the completely flat top design of the LS2 piston. The LS7 piston is cast aluminum and the rings aren't clocked for installation. The ring design, as well as the ring pack, makes clocking unnecessary.

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The PBC uses a tapered sleeve to compress the piston rings prior to installation. The piston/rod assembly is pulled down through the sleeve until the piston skirt pops out at the bottom. It's then ready to install.

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Just as if you were building an engine at home, the LS7's pistons are driven home one at a time and tapped all the way down with the handle of a dead-blow mallet. There is no sign of mass production to be found here.

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One of the coolest tools we've ever seen is the multi-wrenched torque machine, which is used to simultaneously cinch all the fasteners in certain procedures, such the main cap bolts or cylinder head bolts. The machine is connected to a computer that records every bolt's torque rating, and indicates a warning if any one of the bolts didn't meet the torque spec.

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An example of the continuous inspections during the assembly is yet more paint markings on the rod bolts. Each bolt gets a paint daub after it has been torqued to spec. The PBC's engineers weren't sure how long the paint would last on the bolts and whether they'd be visible in 25 years during a restoration teardown.

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As work progresses, the engine starts to take shape. Here, the front cover is cinched into place, indicating the reciprocating assembly chores are complete.

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This a great, low-tech secret of the PBC that contrasts with the computer-controlled torque wrenches: after the front cover is bolted on, a "boat wheel" is attached to the crankshaft as a leverage device that makes turning over the engine a lot easier. The red line, however, is a timing reference. When it's straight up, the crank is in the correct position for the timing chain. Easy!

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The LS7's oil pump is really two pumps in one: a 0.95ci pump for supply (the same spec as the LS2) and a 1.41ci rotor for oil scavenging. The scavenge pump needs more capacity because it will consequently pick up air along with oil.

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Here's a look at the special dry-sump oil pan. Because of the dry-sump system, there are two drain plugs, indicated by the cast-in line running between them. And before you ask, the answer is no: the LS7 pan--and corresponding dry sump system--will not bolt up to an LS1 or LS2 engine. There are too many differences with the front cover, crankshaft and other components.

LS7: The Crate Engine You've Been Waiting For

The folks at GM Performance Parts were on hand at our LS7 assembly line tour to tell us the 500-horse engine will be available as a crate engine right about the time the Corvette Z06 goes into production.

The crate engine package won't include the complete dry-sump oiling system, but it will likely be offered separately. A number of aftermarket systems should work, too, although the factory supply and scavenge outlets don't have conventional or AN-type fittings.

No, it won't be cheap, but then again, this is a hand-built, 500-horse engine with CNC-ported heads, and a whole mess of exotic materials. It sounds perfect for, say, a '70 Corvette or maybe a Pro Touring Chevy II. Don't be surprised to see other Z06 items in the next GMPP catalog too.


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