Gen III GM Small Block Tech

What You Need To Know To Get More Power With GM's New Small-Block V-8

Will HandzelDec 6, 2006
Photo 2/19
That Chevy LS1 small-block V-8 sitting under the hood isn't too bad, but, of course, it would be nice to make some power improvements. Ahead lie the tools and procedures that will make this possible: clarifying the terms used when talking about these engines, examining their architecture, and outlining several steps that can make that desire for more power a reality.

The Gen III V-8 was designed to be used in multiple cubic-inch sizes, to power cars and trucks, to be easy to manufacture and service, and to provide superior durability. It is a seemingly simple design that achieves all of these requirements with impressive power output and efficiency.
Photo 3/19   |   Some of the simple bolt-ons the LS1 Gen III V-8 makes power with include free-flowing airbox components (shown), after-cat exhaust systems, "wet" 100hp nitrous systems, mildly ported stock throttle bodies, a supercharger, and other similar components.
The Gen III small-block was designed from the beginning to be based on either an aluminum or cast-iron engine block. The cast-iron engine blocks came in the trucks, while the aluminum engines went in all the car applications with the thought that cast-iron blocks were needed to handle the rigors of truck usage. Some of the midsize SUVs and SSR trucks now use the aluminum block-based engines, but the fullsize trucks still use cast-iron blocks.
Here is the timeline of the first usages for this engine: The Regular Production Option (RPO), coded LS1, Gen III V-8 was introduced as an aluminum block-based engine in the '97 C5 Corvette. The aluminum block was improved and used as the foundation for the LS6 that powered the '01-'04 Corvette Z06s. The '98-'03 Camaro/Firebirds were powered by LS1s, as was the '04 GTO. The '04 Cadillac CTS-V started out with LS6 power.
The current engine in the '05 CTS-V, GTO, C6 Corvette, and SSR is the 400hp LS2 V-8-considered a Gen IV V-8 engine. The Gen IV is a variant of the Gen III. The Gen IV was not the completely new engine the Gen III was to the Gen I/II small-block V-8s, so much of this discussion applies to both the Gen III and IV V-8 engine families.
The Gen III aluminum block is a tour-de-force of technology. The block has pull-from-the-bottom head bolts, is deep-skirted, uses cross-bolted mains, has built-in crank and cam sensor mounts, and was designed to be as light as possible. The cylinder liners are thin, centrifugally cast, cast-iron inserts that are cast in place when the molten aluminum is poured into the mold. This reduces weight and machining time (not pressing in cylinder liners) and also extremely limits the amount the bores can be opened (because they are thin and are not perfectly positioned in the block). The LS1/LS6 engines come with 3.898-inch/99mm bores that can only be increased about 0.010 of an inch in diameter before fears of cutting through the liner become great.
One of the advantages of the just-released 6.0L Gen IV LS2 aluminum engine block is it has 4-inch/101.6mm bores and can be bored out 0.020 of an inch. Other than having bosses cast in place for the "Displacement on Demand" (DOD) in the lifter valley, the knock and cam sensors moved, and the head bolts being the short versions, the LS2 block is common with the LS1 block.
Photo 4/19   |   If you've got an airbox or after-cat system already, the next step is often a supercharger, like this Magnuson unit bolted on a stock 6.0L LQ4. These roots-style superchargers are perfect for this engine because they deliver approximately 5 psi of max boost and can add a real 100 hp.
In early performance combinations, the aluminum version of the Gen III/IV V-8 had shown itself to be able to stand only so much in street-going applications. Some numbers to put it in context: The stock aluminum block has been known to handle a constant 650 to 700 hp without issue-and this is with the factory torque-to-yield head bolts. Some design changes would allow more, but GM is more concerned with lightweight, fuel-efficient, and emissions-friendly engines. As an aside, there are nitrous Vettes on the street with 550hp engines and 150hp shot systems that are providing reliable service.
The cast-iron blocks appeared in the '99 fullsize GM trucks. They weigh 88 pounds more than the aluminum blocks and have been used as the foundation for engines making more than 1400 hp. Near-stock cast-iron blocks (GM PN 12551366) have been known to handle up to 850 hp in "drivers."
Other than being a bargain from GM Performance Parts, the advantages of the cast-iron blocks are numerous. These blocks are common with the aluminum blocks in their acceptance of components, they can be bored out 0.030 [the 4.8 and 5.3L blocks can be bored to 99 mm and the 4-inch (101.6mm) bores can go 0.030 of an inch over] and offer increased strength at a very low weight penalty. Simply put, just combine a 4-inch bore cast-iron block with a 4.125-inch-stroke aftermarket forged crank and you've got a 403ci bad-boy Gen III that can handle 1,000 hp with few problems.
Photo 5/19   |   Swapping the cam on a Gen III LS1 can be accomplished quickly. This is because unlike the previous small-blocks, the oil pan does not need to be dropped to remove the front cover, and the lifters can be left in the engine.
The stock LS1 Gen III V-8 cast crank, powdered metal rods, and hypereutectic, cast-aluminum pistons are all commonplace large-scale production OE components. None of these would be the first choice of a hot-rod enthusiast, but all the pieces do an amazingly good job of handling 500-plus hp in a performance application. Beyond that, you'll need forged, floating-pin pistons (the stock pistons use a pressed-on pin up to '04), and if you're going with forged pistons, you might as well go with new rods.
Most enthusiasts will go up in stroke if they spend the money on an aftermarket crank. This is one of the great advantages of the Gen III V-8: The engineers at GM raised the cam and left plenty of space in the cylinder block for a little more than a 4-inch-stroke crank. So, no grinding or special machinework is required to go up in arm to gain cubic inches.
Photo 9/19   |   The Gen IIIs were designed for manufacturability, so many of the connectors, fittings, and systems are not familiar to hot rodders, which can lead to a frustrating, expensive experience trying to remove an engine. The book "How to Build High Performance Chevy LS1/LS6 V-8s" has one chapter dedicated completely to removing and reinstalling the Gen III engine. It has more than 160 images to show how to remove the Gen III from GM fullsize trucks and SUVs, along with the Corvette, Camaro, and Firebird.
The cylinder heads are the big story on the LS1 Gen III V-8. Not only do they look serious with their symmetrical "cathedral" intake ports, aggressive exhaust ports, small combustion chamber volumes, and slick investment-cast rocker assembly; they make serious power in just about any application with little work.
GM veterans and brothers Ron and Ken Sperry spearheaded the design and development of the heads. With almost 80 years of GM development experience between them, the Sperrys were allowed to lead their teams to develop the best production head design ever. These heads have been used to support normally aspirated 800hp street nasties, 1,000hp centrifugally blown bruisers, and 1,400hp turbo killers. For more details, check out the sidebar on the head specs for more on this great design.
If there is one drawback to the production heads, it's that the engineering team was only allowed to build one head, and it had to fit all the Gen III V-8 engines. This means the valve spacing and chamber shape on the head are for the smallest bore engines: the high-volume 4.8L and 5.3L truck engines. These engines have 3.780-inch/96mm bore diameters. GM did this to minimize tooling expenses and to maximize its initial engineering focus, knowing full well that it was sacrificing real power. This is a good example of the many everyday compromises a large-scale manufacturing company like GM must make to maximize success, but it also highlights an opportunity for the aftermarket and performance enthusiast.
Photo 10/19   |   Whether in the engine bay or out of a vehicle, the Gen III V-8 is very straightforward to disassemble. For instance, the intake manifold is held on the engine with 10 "nested" bolts. Once unscrewed from the cylinder heads, the intake usually requires slight prying and pops off. No water or oil touches the nylon intake, so this step is completely dry.
The engineering team at GM estimates a set of heads built specifically for the 3.898-inch/99mm, 4-inch/101.6mm, and larger bore spacings would release at least 15 to 25 hp-thinking in terms of the stock engine. A performance engine would obviously see greater gains.
Now, this is no small undertaking. To take full advantage, the intake and exhaust ports would need to be reworked, the rockers and lifters would need to be offset to attain proper valvetrain geometry, and the combustion chamber would need to be considerably altered. Will it happen? More than likely, yes, as the engine has so much groundswell interest and power-producing potential. The question is more when, not if.
Photo 11/19   |   There have been many small changes to the Gen III since it was introduced in '97. One example is the valve covers: The '97-'98 Gen IIIs had perimeter bolts, while the '99-and-later valve covers were center-bolt designs. This makes it easier to identify what year heads and valve covers you are looking at.
The LS1 Gen III V-8 nylon-intake manifold is impressive with its low height, minimal turns, and high-flow numbers. The early LS1 intakes should all be replaced with LS6 or LS2 intakes, as the improvements in manifold volume, throttle size, and port shaping make the LS1 intake a detriment to power output.
The truck intakes have a much different design; they certainly won't win any appearance contests. The main reason they look different is that the inlet needed to be 3 inches higher than the LS intakes in order to clear the cooling fan. The 4.8, 5.3, and 6.0L intakes are all common, so there is no gain from swapping one for another.
The LS2 intake (GM PN 89017648, available from GM Performance Parts) is a bargain, and many believe it flows just as much as the aftermarket intakes. Installing it will require some rewiring work as the manifold pressure sensor is moved from the back to the front, and the factory LS2 throttle body has a different bolt pattern than the LS1 unit. Also, the 90mm LS2 throttle body is electronically controlled, so either an aftermarket, mechanical throttle body will be required or an adapter for the existing throttle body.
Photo 12/19   |   The act of torquing down stretch-to-yield fasteners (which are used on the head bolts, main cap bolts, harmonic balancer, and other major components) goes like this. First, the underside of the fastener head is lubricated, and the bolt is torqued to the minimal level; then using this torque angle socket (shown), a specific amount of additional twist is applied to the bolt. Often, the twist is added in two steps, like on the cylinder head bolts.
The LS1 Gen III V-8 architecture is sensitive to the components that support it. These include the inlet that provides air to it and the tubing that guides the exhaust out of it. The electronic controls [what GM calls the Powertrain Control Module (PCM)] and the calibration inside the PCM are also a big part of the power production of the Gen III V-8.
Since most of these components are built for 95 percent of the population, which doesn't care to hear the engine doing its thing or want that last 5 hp from the combination, there are power increase opportunities here.
Adding small amounts of power is easy with open-element airboxes and smooth-inlet tubes, after-cat exhaust systems, tube-exhaust headers, and calibration reprogrammers. All of these components are relatively straightforward to install, qualifying as "dry" components in the business since they don't require the installer to touch the oil, fuel, coolant, brake, air conditioning, or power steering systems (many of which require special tools, equipment, and knowledge to properly reassemble).
The LS1 Gen III V-8 responds to all of these modifications, but the most impact will come from installing long-tube headers. These headers are complex and expensive to install but point out the choke point on the vehicles. The exhausts are built to be low cost, durable, and emissions compliant, not to generate maximum flow, and the losses in flow do make a big difference in power output.
The long-tube systems usually require a completely new exhaust, with aftermarket catalytic converters and other components, so they are expensive, but if you've made other modifications and want to truly reap all the benefits of the changes, the stock manifolds will need to be swapped out at some point.
Photo 13/19   |   While the LS1 Gen III V-8 is a great engine design, the real mind-numbing components are the cylinder heads. The symmetrical, cathedral intake ports are a result of massive amounts of experience, testing, and innovation. They were built out of necessity to fit between the pushrods, the four head bolts, and other systems but are impressive in their ability to flow air. The design is common between all the cars and trucks through 2005, which makes it easy to swap parts for power. These are GM Performance Parts CNC-ported cylinder heads that will yield additional power.
While the LS1 Gen III V-8 is a new pushrod engine, many of the systems will seem familiar once you start working on them-except for one. The calibration side of the Gen III is not for the faint of heart. The factory controls should be changed with caution. Some of the simple power programmers, like those available from Hypertech, DiabloSport, and others, limit the consumer's access and ability to make changes. This minimizes the chances of causing a problem with the drivetrain.
More advanced calibrating aids-most notably the systems available from LS1 Edit and HP Tuners-allow impressive access to the factory calibrations. But even simple changes to maximum engine rpm, transmission shift line pressures, and the ignition advance can quickly spell disaster. It is strongly suggested you find a reputable, recommended calibrator to assist in getting the correct calibration for your vehicle. Not only does a good calibration make a huge difference in power production, you will notice an improvement in driveability, longevity, and other aspects also.
In general, the Chevy LS1 Gen III V-8 is going to be the foundation for hot-rod engines for a long time to come-and for good reason. It was developed with the goal of being the best production pushrod V-8 ever built. Judging by the interest in the automotive enthusiast community, it is a fitting powerplant to celebrate the amazing 50-year legacy of the small-block engine.
Photo 14/19   |   If you are making any power increases to the Gen III V-8, plan on increasing the flow of oil through the engine with a mild porting of the oil outlet passage and with an increase in the pop-off valve pressure (here being accomplished with a shim under the spring). The LS1 Gen III was designed to operate on a minimum of oil to minimize power losses, so more power means you need more oil.
The information presented here applies to all Hummer H2s and Cadillac Escalades. Powered by the cast-iron block, aluminum-head, 300hp LQ4 6.0L Gen III V-8, these massive rolling statements become much more pleasurable to drive with just a few engine upgrades. Some of the simpler pieces include air inlet and after-cat exhausts, but for a real seat-of-the-pants power infusion, you'll need to bolt on a Magnuson supercharger for a sweet increase of at least 100 hp.
Of all the modifications you can make under that flip-forward hood, a supercharger is the most dramatic. Installing a blower on the LQ4 works great since the engine was built with a 9.41:1 compression ratio-so adding some sub-5-psi boost can be done without changing pistons or encountering engine-damaging detonation (but you must run premium fuel with the blower). The Magnuson unit seems to be the most popular because its system bolts on with minimum hassle and makes durable power.
The Gen III V-8 architecture was introduced to the public as the GM Regular Production Option (RPO) LS1 engine in the '97 Corvette. A GM engine RPO is essentially its name for that vehicle platform, but not its architecture name.
Because of the RPO confusion, the industry has ended up calling every variation of the Gen III V-8 an LS1, which is slightly incorrect.
Internally, GM calls this engine architecture the Gen III V-8, so that's what we're going to call it throughout this story. But as you've probably noticed, the story often references LS1s; that's because everyone in the business knows these engines as LS1s. Whatever you call them, the Gen III LS1 V-8-and the latest version that are being called Gen IVs-make great hot-rod engines, and you're going to be ready to jump into building one.
Summary of the Many Gen I, II, and III Similarities and Differences
In case you are wondering what is similar and what is different on the Gen III V-8 versus the previous Chevy small-block design, here is a chart.
Similarities
* Gen III has the same 4.4-inch bore spacing as Gen I and II
* 90-degree angle spacing of cylinder banks
* Two overhead valves per cylinder
* Valvetrain oiled through lifter gallery/lifter/hollow pushrod system
* Connecting rod crank pin diameter of 2.1-inches
* Lifter diameter of 0.842 inch
* Single-piece rear crank seal (like on later versions of Gen I and II)
* Starter located on lower passenger side of block
* Oil filter located on lower driver side of block
Differences Gen III Gen I and II
Block length 519.0 mm (LS1) 553.2 mm (LT1)
Block width 460.0 mm (LS1) 434.6 mm (LT1)
Block deck height 9.{{{240}}} inch 9.025 inches
Firing order 1, 8, 7, 2, 6, 5, 4, 3 1, 8, 4, 3, 6, 5, 7, 2
Cylinder bank offset 0.9488 of an inch 0.8800 of an inch
Crank main caps 6 bolted – 4 verticle, 2 horizontal, Mostly 2-bolt mains, some splayed with 4 bolts
Distributor DriveNo distributor capability Distributor drive at rear of cam
Sensors Engine block–mounted; No direct electronic crank
and cam location cam sensors
Weight 430 lbs for a complete LS1
(add approximately 88 lbs for iron truck block)
531 lbs for most complete Gen I/IIs
Connecting rod 6.098 inches long 5.700 inches long offset
Piston pin diameter 0.{{{940}}} inch 0.927 inch
Crank thrust bearing No. 3 (center) Rear main bearing
Cylinder head ports All Replicated Mirrored images of each intake
and exhaust ports
Crank flange location 0.040 of an inch closer to bellhousing mount on block than Gen I/II  
Thermostat location Intake side of water pump; Exit side of water pump
Intake design No coolant or hot water passes through oil; Touches intake and oil hits bot tom of intake
Intake construction Intake made of nylon; Intake made of cast-iron or
aluminum
Order through www.cartechbooks.com or call (800) 551-4754.
INTAKE PORT SIZE
Engine Volume (cc's)
LS1 {{{200}}}
LS6 210
LQ4/LQ9 210
LM4/LM7 190
LR4 190
LS2 210
EXHAUST PORT SIZE(S)
Engine Volume (cc's)
LS1 70
LS6 75
LQ4/LQ9 75
LM4/LM7 70
LR4 70
LS2 70
CHAMBER SIZE(S)
Engine Volume (cc's)
LS1 66.67
LS6 64.46
LQ4/LQ9 71.16
LM4/LM7 61.14
LR4 61.14
LS2 64.14
Valvesprings - beehive shape wound from 4.6mm-diameter chromium silicate (Cr-Si) ovate (oval-shaped) wire
Retainers - steel
Locks - 10-degree design, steelCamshaft - roller design made from 5150 steel billet shaft, gun-drilled with a 17mm hole for reduced mass.
Lifters - hydraulic roller, sets of four nested in a plastic carrier guide in order to guide and provide easy installation
Rockers - Investment-cast, stainless steel needle roller bearing pivot nested in investment-cast aluminum rocker arm stand
Pushrods - steel, 8mm-diameter, 0.075-inch-wall thickness
Head gaskets - '97-'98: sandwich design of graphite layers over steel core, '99-and-later: multi-level steel (MLS) gaskets.
Valve Angle - 15 degrees (versus 23 degrees of previous Chevy small-block)
Valve Seat Machined Angles - 30, 45, and 60 degrees to blend into chamber
Distance between Valve Guides - 48.6 mm (1.913 inches) on all heads

Sources

Chevrolet Performance Parts
Detroit, MI 48232
800-577-6888
www.gmperformanceparts.com
Car Tech Books
cartechbooks.com

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