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Here's an inside look at the biggest, baddest small-block ever built by GM
Jul 27, 2005
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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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
As work progresses, the engine starts to take shape. Here, the front cover is cinched into place, indicating the reciprocating assembly chores are complete.
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!
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.
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.
There's a windage tray beneath the oil pan. It is notched to clear the oil pan's suction tube.
The LS7 has a unique, PF48 oil filter that incorporates an internal bypass valve. The filter is the same size as the common PF44 oil filter, but its thread pitch is different so the PF44 can't be mistakenly installed.
The cylinder heads are artfully crafted, CNC-carved blocks of aluminum with cavernous, super-straight tunnel ports. It's hard to believe this a factory-production part.
The heads' combustion chamber volume measures 70 cc and the chambers are fed by gigantic and lightweight titanium intake valves with 56mm faces. The intake valves have 22 percent more area than LS2 valves, but weigh 21 grams less! The exhaust valves are 41 mm across and are sodium-filled.
The heads are placed on multi-layer steel (MLS) head gaskets; they're tall, too. The ports are long to enhance velocity and the valvetrain is a little taller. In fact, the rocker rail is a full 6mm taller than the LS2's (approximately 0.25-inch).
The valve angles of the LS7 are 12 degrees (versus 15 degrees on the LS2). Accommodating this specification and leaving room for uninterrupted flow in the ports requires offset rocker arms on the intake side. Note that the rocker arms are not roller-tipped.
All the bolts of a cylinder head are run down and torqued by one of the big, computer-controlled tools. Each of these tools costs about $150,000, and there are several located along the production line.
The valve covers look similar to other Gen III and Gen IV engines, but with a big difference: the only oil fill port (passenger side) is designed for "fill it once and forget it" use. Except for an oil feed during balancing, the engines leave the PBC dry. They are filled at the offsite hot-test facility and capped with a permanent seal. For the car owner, oil must be added to the dry sump tank. There is no dipstick on the engine or oil pan, either.
The intake manifold, throttle body and fuel rails are delivered as a single part and installed as such. In GM jargon, the unit is called an Integrated Air Fuel Module (IAFM). The fuel rails are the same as the LS2, but the injectors are rated for 40 lb/hr. The IAFM assembly is supplied by Bosch.
The exhaust manifolds are installed on the assembly line, a procedure not always performed on engine lines. We're told the manifolds will bolt up to an LS2 engine, even though the exhaust port shape isn't quite a match--the LS7 manifolds' ports are larger, so there's no worry in blocking the flow path.
A rarity for production engines--and even racing engines--the exhaust manifolds are made from hydro-formed tubular steel. The individual runners of the header tubes meet at a unique quad-outlet collector, which is said to smooth exhaust flow and reduce backpressure.
Ignition coil packs are the same as those on the LS2, which are upgrades from the Gen III design. They're a little smaller and more efficient, but deliver the same spark energy as the previous-style coils.
This shot depicts the final assembly of the LS7 engine. At this stage, it is given a thorough inspection by the builder and a log of the torque sequences, and bar code-scanned procedures are checked. A second inspector who had nothing to do with building the engine will also look it over because a fresh pair of eyes will find things the first person might have missed.
An LS7's last stop in the PBC is the balancing room. The engine is fired up on natural gas fed through the throttle body. The engines are run briefly at 1500 rpm to produce baseline reading. The balance cradle is suspended on a cushion of air when the engine is running. Weight is added to the flywheel or balancer, as needed, with tolerances held at 0.5 ounce.
After balancing, the engine is sent offsite for hot testing, then returned for shipment to the Corvette's Bowling Green, Kentucky assembly plant. This one is ready for an awaiting Z06 body.
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