Inside the LS7

The all-new LS7 in the ’06 Z06 reintroduces the 427-cubic-inch engine to the Corvette lineup. Unlike the previous 427 engine, which was a big-block design, the new 7.0-liter LS7 is a small-block V-8 – the largest-displacement small-block ever produced by Chevrolet and GM, and a tribute to its 50 years as a performance icon.

With 505 horsepower (377 kw) and 470lb.-ft. of torque (637 Nm), it also is the most powerful passenger car engine ever produced byChevrolet and GM. The LS7 is easily identified under the hood by red engine covers with black lettering. The LS7 shares the same basic Gen IV V-8 architecture as the Corvette’s 6.0-liter LS2, but it uses a different cylinder block casting with pressed-in steel cylinder liners to accommodate the engine’s wide, 104.8-mm-wide cylinder bores.Compared with the LS2, the LS7 also has a different front cover, oil pan, exhaust manifolds and cylinder heads –among many other components.

Internally, the LS7’s reciprocating components make use of racing-derived lightweight technology, including titanium connecting rods and intake valves, to help boost horsepower and rpm capability. The rpm fuel shut-off limit is 7000rpm. The LS7’s details include:

 

Dry-sump oiling system
Unique cylinder block casting with large, 104.8-mm bores and pressed-in cylinder liners.Forged steel main bearingcaps
Forged steel crankshaft
Titanium connecting rods with 101.6-mm stroke. Cast aluminum flat-top pistons
11.0:1 compression

High-lift camshaft Racing-derived CNC-ported aluminum cylinder heads with titanium intake valves and sodium-filled exhaust valves Low-restriction air intake system Hydroformed exhaust headers with unique “quad flow” collector flanges.

 

One of the clearest examples of the LS7’s race-bred technology is its use of titanium connecting rods. They weigh just 464 grams apiece, almost 30 percent less than the rods in the LS2 V-8. Besides lightweight, which enhances high-rpm performance and rpm range, titanium makes the rods extremely durable.

The LS7’s CNC-ported aluminum cylinder heads are all-new and designed to meet the high airflow demands of the engine’s 7.0-liter displacement, as it ingests approximately 100 cubic feet more air per minute than the Corvette’s 6.0-liter LS2 V-8 – an 18-percent increase in airflow. Consequently, a hydraulic roller camshaft with .591/.591-inch valve lift is used to allow plenty of air to circulate in and out of the engine.

To ensure optimal, uninterrupted airflow, the LS7’s heads have straight, tunnel-like intake runners. Very large by production-vehicle standards – even racing standards – they are designed to maintain fast airflow velocity, providing excellent torque at low rpm and exhilarating horsepower at high rpm.

The heads feature 70-cc combustion chambers that are fed by huge, 56-mm-diameter titanium intake valves. The lightweight titanium valves weigh 21grams less than the stainless steel valves used in the LS2, despite the valve head having 22 percent more area.

They are complemented by 41-mm sodium-filled exhaust valves, vs. 39.4-mm valves in the LS2. To accommodate the large valve face diameters, the heads’ valve seats are siamesed; and, taken from experience with the engines of C5-R racecars, the LS7’s valve angles are held at 12 degrees – vs. 15 degrees for the LS2 – to enhance airflow through the ports.

The LS7 has a dry-sump oiling system designed to keep the engine fully lubricated during the high cornering loads the Corvette Z06 is capable of producing. An engine compartment-mounted 8-quart reservoir delivers oil at a constant pressure to a conventional-style oil pump pick-up at the bottom of the engine. The pressurized oil feed keeps the oil pick-up continually immersed in oil at cornering loads exceeding 1 g.

Oil circulates through the engine and down to the oil pan, where it is sent back to the reservoir via a scavenge pump. The large-capacity reservoir, combined with a high efficiency air-to-oil cooler, provides necessary engine oil cooling under the demands of the engine’s power output. With the dry-sump system, oil is added to the engine via the reservoir tank – which includes the oil level dipstick.

The LS7’s dry-sump system was developed and tested on racetracks in the United States and Europe , including Germany ’s famed Nürburgring. And while common in racing cars, the Corvette Z06 is one of just a handful of production vehicles – and the only production Corvette – ever to incorporate such a high-performance oiling system.

The piston assembly for the 2006 Corvette Z06 LS7 7.0-liter V-8 engine is one of the latest examples of race designs carrying over to production GM engines. Almost every aspect of the short skirt, high strength pistons and titanium connecting rods used in the 505 horsepower power plant is developed through race design know-how.

 

Thanks to racing experience GM engineers have brought one of the most advanced design piston and rod assemblies to a production engine. “Besides light-weight, the LS7 piston assembly has an abundance of features built-in through race experience,” said Roger Duguay, chief engineer for GM small block engines. “Full floating pistons with valve reliefs and lightening pockets, plasma moly rings, tapered wall pins, high strength chromium nitrided titanium rods just begin to highlight the racing DNA of this assembly.”

The full-floating piston is made of eutectic aluminum alloy and is CNC machined for balance and tolerance consistency. For durability the top land is anodized. Between the first and second ring lands is a pressure balance groove, another racing carry-over, to control blow-by and oil consumption at high speed. Piston tops are flat with symmetrical valve reliefs providing opportunities for a stroker crank or higher lift. A polymer coating on the skirts to reduce scuffing creates an almost negative interference fit in the bore.

The ring pack uses thin rings for high speed sealing control. A 1.2 mm top compression ring is used with a plasma moly face for superior sealing and durability. The second compression ring is also 1.2 mm thick and is made of ductile or high strength iron. The three-piece oil control ring is 2.0 mm thick and is made of nitrided steel for superior wear control and spring force longevity. Nitriding also enables lower ring tension resulting in more power due to reduced friction.

Little was spared when it came to developing the connecting rods. The rod is made of a titanium aerospace alloy and uses twelve-point doweled cap screws. The rods are heat treated and have a chromium nitride coating for surface durability. The coating is applied to the thrust facing areas via plasma vapor deposition (PVD) – a process taking 12 hours to apply. Each rod has three weight pads for precise balance. Blind holes are used, to eliminate stress areas, in conjunction with a heat treated style cap screw with a neck down shank for consistent clamp and controlled stretch. The LS7 rod weighs just 464 grams which is almost 30 percent lighter than the similar forged powder metal rod in the base engine Corvette.

Racing has always been on the forefront of reducing component weight. “Racing knowledge transfer gave us the basic design elements for the LS7 piston assembly,” said Tom Halka, development engineer for GM small block engines. “Thanks to GM’s vast technical resources and racing background we now have a light, high speed assembly that balances reliability and durability with performance. What we learned with this assembly we will apply to other GM engine programs.”

SPECIFICATIONS

Engine

Type:
7.0-liter (427.7 cu . In.) OHV V8 LS7 for the 2006 Corvette Z06

Horsepower:
505 (377 kW) @ 6300 rpm (SAE certified )

Torque:
470 lb.-ft. (637 Nm) @ 4800 rpm (SAE certified)

Bore x stroke:
4.125 in. x 4.00 in. ( 104.8 mm x 101.6 mm)

Compression ratio:
11.0 :1

Fuel shutoff:
7100 rpm

Piston

Type:
Flat top, short skirt, with valve reliefs and lightening pockets, anodized top land, second land with pressure balance groove

Material:
High strength aluminum alloy, T-7 heat treat, polymer coated skirts

Compression height:
30 mm

Weight:
482 grams

Piston-to-valve clearance:
Intake: 8 mm Exhaust: 7 mm

Piston pin

Type:
Full floating, taper wall

Material:
High strength steel alloy, nitrided

Length / diameter
58 mm / 23.5 mm

Weight:
132 grams

Retainer:
Round wire ring, chrome silicon steel

Piston rings

Top compression:
1.2 mm (.0472 in.) symmetrical barrel face and twisted, plasma moly coated

Second compression:
1.2 mm (.0472 in.) high strength ductile iron, taper face napier style

Oil control:
2.0 (.0787 in.) mm stainless nitrided steel, three piece, low tension

Connecting Rod

Type:
Forged I beam, stepped down pin end, blind cap hole, alignment sleeve

Material:
Titanium aerospace alloy

Center to center length:
154.1 mm

Bolts:
12 point cap screw, heat treated, high strength steel alloy, necked down shank

Weight:
464 grams

Rod Length-to-Stroke:
1.5:1

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