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With the 2005 model year, the LS1 is superceded by the 6.0-liter LS2.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.

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While based on the Gen III architecture, GM calls the LS2 (and the variants to come) a Gen IV small-block. This collection of parts represents most of what separates the LS2 from the LS1.

The LS2 has a new block casting. While still made of high-strength aluminum, several sensor locations have been revised to accommodate GM's Displacement on Demand cylinder deactivation technology.

One of the casting changes included relocating the provision for the camshaft position sensor (CMP) from the rear of the block to the front. The CMP determines the relationship of the cam to the crankshaft to determine, via the PCM, which cylinder is ready for fuel. It also detects misfires.

In the 6.0-liter applications, including the Corvette, GTO and SSR, the LS2's cylinder bores measure 4.00 inches in diameter. The LS1's bores measured 3.90 inches.

The LS2's crankshaft is essentially the same sturdy, 3.62-inch-stroke forging as the LS1's. Previous LS6 engines were balanced to a higher degree than LS1 engines; we don't know if that will be the case with the LS2, which incorporates many of the LS6's attributes.

Pistons for the LS2 have a true flat-top design. Ring tension has been altered, compared to the LS1, to reduce the tension and free up horsepower.

The pistons are connected to cast rods via full-floating wrist pins. This was done to reduce the piston slap often heard in LS1 engines. Though not proven to be detrimental to the engine, the slap noise nonetheless caused customer complaints.

For Corvettes, there's an all-new oil pan design. It eliminates the winged style of the LS1 pan as engineers devised a better internal design to fight high-g oil starvation.

New-design baffles inside the Corvette's oil pan are designed to keep the oil pump pickup submerged in oil during high-load cornering maneuvers. The elimination of the previous-style pan's wings also reduces the oil capacity of the pan by one quart.

Simply put, the LS2's cylinder heads are from the Corvette Z06 LS6 engine, including the same unshrouded-valve chamber design and port configurations. With the revised flat-top piston, however, compression jumps to 10.9:1--up from 10.5:1 in the LS6.

Like the LS6 engine on which they were first proven, the LS2's heads have unshrouded valves. They measure 2.00 inches on the intake side and 1.55 inches on the exhaust.

Nothing revolutionary here: The LS2's composite intake manifold is largely the same as the LS1's, although it's been changed to reflect the engine's various sensor relocations. It also will mount the throttle body on a slightly upward angle to prevent water puddling at the base.

A new, electronically-controlled throttle (ETC) is part of the LS2's standard features. ETC has been used on the Corvette and some other Gen III engines, but all LS2s will have the system. Instead of a traditional throttle cable, an electric motor attached to the throttle body actuates the throttle blade. The throttle opening itself measures 90mm.

The familiar coil-near-plug ignition system returns, but the coils themselves are new. They are more efficient and require less energy to produce the same spark as the previous design.

One of the LS2's more interesting innovations is the development of new, lighter exhaust manifolds. By reducing the interior wall thickness of the ports--and a few other changes--the manifolds are fully one-third lighter than before.

Our photo shoot of LS2 components also netted a close-up look at a cutaway version of the engine that GM built for display purposes.

This inside look at one of the LS2's cylinders shows the relationship of the flat-top piston, the unshrouded valve and the design of the intake port.

Another look at the cutaway engine reveals an inside look at one of the new, thinner-wall exhaust manifolds.

This is a significant change over the original LS1's heavy, twin-walled manifolds.

A running change with LS1 engines, the LS2 features a revamped water pump that is sealed better to prevent leaking. Note, too, the slightly upward position of the throttle body and the position of the electronic throttle control motor on the throttle body.

We caught several new Corvette-bound LS2s at a shipping point recently. Check out the bolted-on lift points. The engines are built in St. Catharines, Ontario.

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.

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In 2005, GM's family of extended-wheelbase mid-size SUVs, like the Chevy TrailBlazer EXT, receives a version of the Gen IV V-8 with Displacement on Demand.

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.

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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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