Chevy's New LS7. The Best Chevy V-8 Ever?
The LS7 shares the architecture which debuted with the celebrated LS1 in 1997, maintaining the LS1/2/6 engines' external dimensions, though nearly every component is all-new or revised for durability and power production. The block is a unique casting, designed to accommodate the 4.125-inch bore pressed-in dry cylinder liners. Main caps have been upgraded from the powdered metal material to forged steel, located and retained by dowels and six fasteners at each cap. That's some serious structure downstairs. Final block machining is carried out with torque plates installed, and main bulkhead fasteners torqued to specs.
The bigger bore is part of the equation that equals 427 cubic inches in the new LS7 - the balance is provided by the new 4.000-inch stroke crankshaft. Forged from 4140 chromium molybdenum steel with rolled fillet radius journals, it's essentially what we'd consider a race crank, far beyond the 10-series carbon steel undercut fillet forged production cranks of yesterday.
While the crankshaft material is impressive, the connecting rods are nothing short of exotic, being crafted from lightweight titanium, a first for a domestic production engine. Strength, fatigue life, and weight advantages make it the material of choice over the powdered metal rods used in the other current small-blocks. Rod weight is dropped to a flyweight 480 grams, a 30 percent savings in mass.
Topping the rod is a flat-top piston helping the LS7 achieve a compression ratio of 11:1. The piston features a skirt coating to reduce bore friction, and hard-anodized ring lands, which enhance durability and temperature resistance. Note the short compression height and the lightweight reactive ring pack; pins are full-floating.
The LS7 cylinder heads are a new design, and come fully CNC ported, setting a new benchmark for 2-valve performance. These heads are a key to the LS7's power production, with intake flow rates up 43 percent compared to the LS6/LS2 cylinder heads, while the exhaust notches up for a 26percent gain. These are serious cylinder heads, even by hardcore hot-rodder standards, and are far beyond anything ever seen in production.
Reports peg the intake port flow in the area of 360 cfm as delivered at the engine's peak valve lift, putting the flow capabilities in a league of its own. Technical highlights here include a raised runner with substantially enlarged cross section, full CNC porting, a 2.20-inch valve, and valves set at a 12 degree angle, in contrast to the LS 1/2/6's 15 degrees or the original smallblock's 23 degrees. Note that the familiar cathedral- shaped entrance of the LS1 is gone.
The deep CNC-ported exhaust ports are said to deliver 214 cfm of air flow at 28 inches of water depression. Also visible here are the "Beehive" shaped valvesprings, which reduce critical mass and are less prone to harmonic disturbance than conventional parallel-wound springs. The small diameter retainers also reduce mass at the valve side of the system.
As with the other working surfaces of the LS7 cylinder head, the 70cc combustion chamber is fully CNC-ed to a glorious flow-enhancing form. The combo of 2.20-inch intake and 1.610-inch exhaust valves fills the chamber to take maximum advantage of the available bore size. The spark plug is angled towards the exhaust valve as is standard procedure in aftermarket race heads, and is positioned deep in the chamber for a quick burn. Ample quench areas at each end of the chamber maximize combustion efficiency.
The cylinder heads are sealed to the block with multi-layered steel (MLS) headgaskets, a configuration which has become popular in the performance aftermarket for its bullet-proof seal.
The valves are far from standard fare, with the intake being made of titanium, dropping the weight 22 grams when compared to the LS2 units. The exhaust valves are also lightweight pieces, featuring hollow sodium-filled stems to reduce weight and aid heat transfer. The valvestems have been lengthened to allow for the flow enhancing, raised deep port, while accommodating the 0.591-inch valve lift.
The rockers are unique high-ratio pieces, providing a mechanical advantage of 1.8:1, as opposed to the 1.7:1 found on other Gen III and IV engines. Trunions are rollerized, while the body is designed for extremely low inertia and high strength. To route the pushrod away from the intake port walls, the intake rocker (left) is offset by 9mm, eliminating the compromise normally imposed by the pushrod pinch restriction.
Feeding the massive cylinder head port flow is an all-new intake, required to mate with the enlarged and raised ports of the LS7. The design mirrors the excellent earlier units, featuring cross-ram runners molded in a thermally advantageous polymer. Revisions to cross section, runner length, and plenum design match it to the LS7's requirements.
As with other Gen III and IV variants, the manifold is equipped with a large single throttle body mounted to the front. To supply the increase in displacement and airflow requirements, the throttle body has been enlarged to 90mm.
This cutaway illustrates the smooth streamlined shape from the intake runner into the beautifully-formed intake port. Notice that even without the older engines' cathedral roof, the injector targeting is directly to the back of the intake valve.
Another first for a domestic production engine with the LS7 is the use of a "dry-sump" oiling system. The front-mounted gerotor oil pump features two stages. The pan is evacuated by the scavenging stage, and the oil is fed to a remote reservoir tank. The reservoir allows a continuous supply to accumulate, and any air is separated, providing the pressure side of the pump with an uninterrupted and reliable source of lubricant under the most demanding driving conditions. This inside view of the sump illustrates the routing, with casting passages directing the scavenged oil flow from the pickup to the scavenge stage of the pump's port at the front of the pan. At the other side of the pan, the oil is routed to an exit at the side from the scavenge stage, and oil is drawn back into the pressure stage via the adjacent passage and supplied to the engine. Slick.
The two stages of the gerotor oil pump are clearly visible in the GM cutaway. The pump is driven directly off the crank snout, eliminating auxiliary drives from the camshaft.
Providing the exhaust scavenging are hydro-formed steel tubular exhaust headers. The individual header tubes meet at a unique quad-outlet collector flange at the end of the header outlet. From there, exhaust is routed by a smoothly-tapered extension into a "wide-mouth" catalytic converter. The design greatly reduces the engine's backpressure.
LS7 SPECIFICATIONS & Technical Highlights
Engine type: cam-in-block 90-degree V8
Block configuration: cast aluminum with pressed-in cylinder sleeves and 6-bolt, forged steel main bearing caps
Bore x Stroke (mm / in): 104.8 x 101.6 / 4.125 x 4.00
Displacement (L / cu in): 7.0 / 427
Crankshaft: forged steel
Connecting rods: forged titanium
Pistons: cast aluminum
Compression ratio: 11.0:1
Cylinder heads: CNC-ported aluminum; 70cc chamber volume
Exhaust: Hydro-formed tubular header
Valve size, intake (mm / in): 56 / 2.20 (titanium)
Valve size, exhaust (mm / in): 41 / 1.61 (sodium-filled)
Camshaft: hydraulic roller; 15mm (.591 in) lift (intake and exhaust)
Rocker arms: 1.8:1 offset (intake only)
Air intake: composite manifold with 90mm single-bore throttle body
Fuel: premium required. 91 octane minimum
Horsepower: 500 (373 kW) @ 6,200 rpm
Torque (lb-ft): 475 (644 Nm) @ 4,800 rpm
Engine redline(rpm): 7,000
CAM LIFT INT/EXH DUR @ 0.050 LOBE SEP
LS1 0.497"/0.498" 199/208 119
LS6 2001 0.550"/0.550" 204/218 117.5
LS6* LS2 0.525"/0.525" 207/217 116
LS7 0.593"/0.588" 211/230 TK
* 2nd design LS6
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