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LS2: An Inside Look

We open it up to see what makes the new Gen IV small-block tick

When it was introduced for the 1997 model year in the then-new fifth-generation Corvette, the Gen III small-block was indeed a revolution. It was the first redesign of the basic small-block architecture since Chevrolet introduced it in 1955.

Although it retained the characteristic 4.4-inch bore centers, there was nothing else really the same between the old and the new. Not surprisingly, there was some initial trepidation on the part of enthusiasts. After all, several generations had grown up with the ubiquitous small-block Chevy. Its performance, reliability and affordability were the measures against which other engines were compared.

It didn't take long, however, for those same enthusiasts to be swayed by the new LS1. Like the original small-block, it was powerful, reliable and has since proved itself a fantastic foundation for extracurricular horsepower exploration--heck, you can get an extra 100 horses out of an LS1 just by staring cross-eyed at it.

With the 2005 model year, the LS1 is superceded by the 6.0-liter LS2. It goes into the new 2005 Corvette, as well as the '05 Pontiac GTO and Chevy SSR. It's rated at 400 horsepower and 400 lb.-ft. of torque, with a high, 10.9:1 compression ratio and a 6500-rpm redline. GM calls the architecture for the LS2 (and its truck-oriented Vortec variants) the Gen IV small-block. We think that's a bit of a stretch (you'll understand why shortly), but it nevertheless opens a new chapter in late-model GM performance.

FAMILIAR FOUNDATION

Like we said, GM says the LS2 is built on the new Gen IV small-block architecture. The primary difference between it and the previous Gen III engines is a new block casting. It actually is just a revised version of the Gen III's cylinder case. In fact, the blocks are so similar that many of the Gen III parts carry over, including LS6-style cylinder heads used on the LS2. Here are the differences between the Gen III and Gen IV blocks:Aluminum and iron (truck) versions are cast with new oil galleries to facilitate Displacement on Demand technology (see sidebar story).

Engine knock sensors relocated from cylinder bank valley to external locations.Camshaft position sensor relocated from the rear of the block to the front. Cylinder bores increased from 3.90 inches to 4.00 inches (LS2 applications). Similar to the LS6 block, the PCV valve was moved from the rocker covers to inside the valley.

The remainder of the block's features, from the six-bolt main bearing cap design (four vertical bolts and two cross-bolts) and deep-skirted case remain unchanged.

At the bottom of the block, LS2 engines installed in Corvettes receive a revised oil pan. Redesigned interior baffles in the pan are designed to ensure an adequate oil supply to the oil pump pick-up during high-load cornering maneuvers. The previous Corvette/LS1 combination used a "gull wing" oil pan design, but oil starvation was an issue that more than one enthusiast encountered on the racetrack. With the new, wingless oil pan design, the Corvette's oil capacity is reduced from 6.5 quarts to 5.5 quarts (with a dry filter).

SHORT BLOCK

Complementing the revised engine block is a new reciprocating assembly for the LS2. The crankshaft still delivers a 3.62-inch stroke, but the pistons have a true flat-top design and rings with lower tension. Lower tension reduces friction to free up horsepower.

The LS2's pistons also have full floating wrist pins that help reduce the piston "slap" noise that's common to Gen III engines. Interestingly some customers, particularly truck owners, have complained about piston slap, but there's no real evidence to indicate it causes premature engine wear--we know of a couple Gen III-powered GMC pickups at the GM Proving Ground, outside Detroit, that each have more than 400,000 miles on their original Vortec engines.

Another LS6 carryover part is the high-lift camshaft, which helps greatly in the department covered by the next section of our story.

CYLINDER HEADS

The new, 6.0-liter LS2 taps into a pair of proven winners in the breathing department: the Corvette Z06-derived LS6 cylinder heads. Compared to the standard LS1 heads, the LS6-style lungs feature raised intake ports and a combustion chamber design with unshrouded valves. This design, GM claims, when combined with the engine's flat-top pistons, produces a more efficient swirl of the air/fuel mixture. This efficiency allows a higher, 10.9:1 compression ratio--vs. 10.1:1 on the LS1 and 10.5:1 on the LS6--helping the engine attain 400 horsepower and, we're told, better fuel economy than the smaller-displacement LS1.

Like the LS6, the LS2's valves measure 2.00 inches for the intake and 1.55 inches for the exhaust. The valve springs are designed to handle the engine's 6500-rpm rev range. It's the engine's comparatively high compression ratio--a level not seen in some time on a performance-oriented V-8--that surely will have turbo and supercharger manufacturers wondering how much boost can be put to the LS2 before it arrives at Detonation City. At first blush, we'd think not too much!

THROTTLE BODY AND INTAKE MANIFOLD

All Gen IV small-blocks receive a new throttle body; for the LS2 it's a huge, single-blade 90mm design that incorporates a motor to actuate the throttle's operation with electronic throttle control (ETC).

All LS2 engines will have electronic throttle control, which dispenses with the traditional cable-operated throttle operation. Instead, input from the gas pedal tells the computer how much throttle movement is needed.

Those with an extra-large throttle body on their high-powered LS1 (or LT1 for that matter) know that single-blade designs can be a little touchy, but GM says ETC helps ensure the big, 90mm throttle body provides smooth, predictable performance. It also eliminates the need for an idle air control motor, cruise control module and the "throttle relaxer" for traction control.

The LS2's throttle body is mounted to the intake manifold on a slight upward angle to reduce water puddling at the bottom of the throttle body. The manifold itself isn't revolutionary; just an evolution of the cross-over plenum design of the LS1 and LS6. As with the Gen III versions, the LS2's manifold is made from lightweight composite material and comes in basic black.

By the way, if you've ever questioned the efficiency of this manifold design, you'll want to take a look at the new, three-valve version of the 4.6 "cammer" motor in the coming '05 Mustang; its intake manifold looks nearly identical--including the front-and-center throttle body location--to the LS1/LS6/LS2 design.

EXHAUST MANIFOLDS

A new exhaust manifold design is used for the LS2, bringing a "best of both worlds" advantage--improved flow and reduced mass. GM tells us the new manifolds are fully one-third lighter than previous designs.

Much of the change comes from reducing the wall thickness of the manifold's outlets from 4mm to 3mm. This change contributed to the overall weight loss, while give the interior passages a 4 percent increase in flow.

There are other minor design tweaks, too, to accommodate revised emissions equipment, but it's the lighter, improved flow design that is the newsworthy item here.

ACCESSORIES AND IGNITION

Many components that are standard on the LS2 found their way into production on late versions of Gen III engines. The water pump, for example, carries over, but it is different from early LS1 engines. Its revised design, with improved sealing, is said to greatly reduce the chances of a leak (it weighs less, too). Also, a stronger timing chain was incorporated into Gen III production and it carries over to the Gen IV. All-new to the Gen IV engine, however, is an improved ignition coil pack system.

The ignition system is still a coil-near-plug design, but the coil packs are more efficient and require less energy to deliver virtually the same spark energy as the LS1's coil packs.

FINAL THOUGHTS

Yes, the LS2 has all the material to build on the success of the LS1 and take GM performance to exciting new levels. The rumors about the next Corvette Z06 model indicate the 400-horsepower level of the '05 engines is truly just the beginning.

Generation Gap

To General Motors, the first-generation small-block includes those Chevy engines from 1955 that do not have the LT1-style configuration. The LT1 engines, produced only from 1991-1996, feature unique cylinder head and intake manifold designs to accommodate reverse-flow cooling.

The Gen III small-block includes the 1997-introduced LS1 and all its variants, including the LS6 and the seemingly infinite number of Vortec truck engine versions. Interestingly, GM calls the Vortec 8100 (8.1 liters/496 cubic inches) a "big block," even though it is built on the same architecture as the small-block LS1.

With 2005, the Gen IV engine is born in cars and trucks. It is architecturally similar to the Gen III engine.

Displacement on Demand:

Coming to a muscle car near you?One of the features on some V-8-powered midsize GM SUVs for '05 is an interesting new technology called Displacement on Demand (DOD). In a nutshell, DOD shuts down half of the engine's cylinders to save gas. GM claims the system is worth up to 8 percent better fuel economy.

The system works by deactivating the engine's valves on alternating cylinders, effectively creating a V-4. Unique lifters with special plungers affect the change after the computer determines the engine's operating parameters meet the deactivation requirements. This is generally in light-load, highway cruising driving conditions; full-throttle is always under V-8 power.

GM says the system is so seamless, it's virtually undetectable. There's no indicator on the dash to tell the driver when the engine is in four-cylinder mode.

Will DOD filter down to cars like the Corvette and GTO? Probably; most of the Gen IV engine block's revisions over the Gen III were made to accommodate DOD components. Interestingly, Chrysler already uses a version of this technology on its new Hemi-powered Chrysler 300C and Dodge Magnum. And with gas prices continuing to hover at record prices, we don't see a reasonable reason not to embrace DOD.

It's, like, guiltless performance.

At a Glance: 2005 LS2

Engine type OHV V-8; aluminum block and heads; 6-bolt main bearingsDisplacement 364 cu in / 6.0 literBore 4.00 in / 101.6 mmStroke 3.62 in / 92 mmCompression ratio 10.9:1Fuel delivery Returnless, sequential port fuel injectionRedline 6500 rpmHorsepower 400 @ 5200 rpmTorque (lb. ft.) 395 @ 4000 rpm

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