LS1 Block Basics Everything You Need to Know About GMs Gen III by asafwewe


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									LS1 Block Basics - Hot Rod                                                                       Page 1 of 6

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LS1 Block Basics
Everything You Need to Know About GM’s Gen III and IV Engine Blocks
By Will Handzel
Photography: Will Handzel
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  This is a good overall look at the Gen III V-8 block design. Like many of the components that install
  on the block, the main caps are swedged between the two sides of the skirted portion of the block. This
  interference fit allows the blocks to be built without dowels to hold the mains in place while
  maintaining the rigidity of the overall package.
The General Motors small-block Gen III LS1 V-8 has been around since 1997, but many enthusiasts are
still learning about its great features. Because of that, whether you are working on a Gen III V-8 project
or not, you’ll want to save this article since it’s loaded with tons of engine-block information. It will
show you which Gen III V-8 engine blocks are desirable, identify them via casting and service part
numbers, and then give tips on how to integrate the block you choose into your existing Gen III engine
plans. This article will also touch on the Gen IV V-8 engine blocks as that engine architecture was
introduced in the ’05 model year as an improved version of the Gen III V-8 design. Much of the
information shown here is excerpted from the recently released book, How to Build High Performance
LS1/LS6 V-8s, by Will Handzel, so if you want to know more about the Gen III V-8 engine family, get
a copy of the book at

Block Details
The Gen III V-8 was introduced in the ’97 Corvette as the regular production option (RPO) code LS1,
and it struck a chord. That is probably why many enthusiasts call their Gen III engines “LS1s” no matter
what RPO was used to order the engine (there are many RPO codes for the Gen III engine, as seen in the 4/18/2006
LS1 Block Basics - Hot Rod                                                                      Page 2 of 6

attached chart). Whatever you call your Gen III small-block, you should know the LS1 came with an
aluminum block loaded with groundbreaking features.

  All wired up on the dyno, the Gen III/IV isn’t much to look at, but it’s a stout package that can support
  a lot of power.
The LS1 block is quite different from previous small-block designs. Most of the internal parts, like the
crank mains, front and rear covers, and oil pan, are designed to “find their own home,” which simplified
the machining process and eliminates the need for dowels in many locations. A good example of this is
the crank main caps. They swedge between the block skirt walls to locate them in a scheme GM
engineers call snap-fit cross-bolting. The cross-bolting refers to how each one is held in place with four
vertical and two horizontal bolts.

Another different aspect is the extra-long torque-to-yield head bolts that thread deep into the block to
minimize bore distortion and minimize the clamping load variations often found in large-scale assembly.
A deep-skirted bottom end allows for cross-bolted mains and minimizes noise emission, integrating with
a stressed-member cast-aluminum oil pan to further stiffen the powertrain combo of the engine and

  The cylinder heads are attached to the block with four bolts per cylinder and use multilayer steel head
  gaskets. The cast-aluminum cover that seals the hot oil in the lifter valley from the bottom of the intake
  adds to block structure and houses two electronic knock sensors.
Another new feature was a raised camshaft to clear 4.000-inch-stroke cranks in case GM wanted to use
these in future applications. In major departures, four cylinder-head bolts are used per bore versus the
previous small-block’s five per cylinder, and an oil passage runs the entire length of the block to transfer
oil from the gerotor oil pump driven off the front of the crank. A separate valley-plate cover is used to
improve block structure. It also simplifies the cylinder head installation (they only bolt to the head/block
mating surface), seals the bottom of the intake from the engine oil, and provides a mounting spot for two
electronic knock sensors nested deep in the lifter valley. The other electronic sensors include crank and
cam position sensors permanently mounted on the block. To minimize oil leaks, planar mating surfaces
are used where two components meet (like at the mating point of the oil pan to the front cover). Also, all
gaskets are single-use, aluminum-compression type to maximize sealing capability.

As a final exclamation point on the design, this block turned out to be lighter, smaller, more rigid, and
more usage-flexible than any other production small-block V-8 GM has ever built. 4/18/2006
LS1 Block Basics - Hot Rod                                                                     Page 3 of 6

    The Gen III V-8 uses long head bolts to help isolate the bore distortion caused from torquing the head
    bolts. This cutaway shows the thin coolant passage between the cylinders.
Cast Iron or Aluminum?
While the truck versions of the Gen III, which were phased into the truck/SUV lineup beginning in
1999, are made of cast iron for severe-duty applications, they have the same set of features as found on
LS1 aluminum blocks. The SSR and some of the midsize SUVs are now built with aluminum-block Gen
III engines, but the fullsize trucks and SUVs still have iron blocks. The iron version of the Gen III block
is approximately 88 pounds heavier than the svelte, 116-pound aluminum block. The iron block is a not-
too-shabby 204 pounds, so you’re probably wondering why anyone would run an iron block if the
aluminum block is so lightweight.

Well, if you are making more than 700 hp (900-plus is routine today), the aluminum block starts to
become a liability to long-term health. Simply put, the aluminum block was not designed to support the
power the rest of the engine has shown itself capable of producing. The iron block, though, has been
known to withstand well over 1,400 hp with a few additions/modifications, and it will handle a little
over 1,000 hp in factory trim.

While these big dyno numbers might seem ludicrous, they’re not. The rotating/reciprocating assembly,
cylinder heads, valvetrain, oiling system, ignition, electronic management and other base systems on the
Gen III V-8 are the best pushrod design and execution ever. Period. They allow massive amounts of
power to be generated in very civil packages, which is why block selection is critical to ending up with
an engine that makes ridiculous power with a minimum of heartache.

  The engine block’s casting number on the rear of the driver-side cylinder bank of every Gen III/IV V-8
  block will tell you what you’re looking at. Refer to the accompanying chart for block casting numbers
  and service part numbers.
So what does this mean to the average enthusiast? Well, if you’re modifying a ’98 Camaro with a set of
CNC heads, a cam, and some headers for a 520hp package, your stock aluminum block should work just
fine. But if you’re bolting a big centrifugal supercharger on your C5 Vette with visions of a streetable
700 hp, you should make some modifications to the block. In fact, if you want factory durability, you
should be considering taking the 88-pound hit to swap in the iron block. 4/18/2006
LS1 Block Basics - Hot Rod                                                                         Page 4 of 6

But that’s getting ahead of many choices that are on the table. While the overall horsepower you intend
to make with your Gen III V-8 is key, issues like the engine’s purpose (drag, circle track, or road racing;
offroad or street usage), required durability, cost, and allowable weight need to be addressed.

LS1 Block Basics (cont.)
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       > Here’s a good bit of info to know: The ’97 to mid-’99 LS1 block (bottom) should not be used for
       high-performance applications.
Anger Time
If you are building an all-out drag racing engine, the length of time the engine will be used in anger will
be much, much less than a circle track or road racing engine or even a hot street engine. This means the
necessary foundational stability of the block and the amount of heat the engine will need to shed during
its usage is very different, as is how much wear and tear the engine will need to withstand between
servicing. In general, the stock LS1 block is not used in high-powered drag racing applications, not
because of the block’s strength, but because the bores cannot be machined out much beyond their stock
99mm sizes.

There are inserts available for a block that has had a lot of material removed from the cylinders to
achieve a larger bore. They seem to work in short-cycle, drag racing applications, but for more street-
type use, it’s probably a better idea to order a 4.125-inch bore C5-R GM Racing Gen III aluminum block
or wait a few months for the new LS7 block (derived from the C5-R block). These blocks come with
siamesed bores and bore liners pressed into the block, unlike production aluminum blocks that have
cast-in-place liners.

     The gerotor oil pump for the Gen III and IV V-8s slides over the snout of the crank and bolts to the
     front of the block. The driver side of the pump casting has a passage to feed pressurized oil through a
     galley in the block that runs to the back. Before getting to the back of the block, the oil travels down
     through the oil pan rail to the oil filter, then back up through the rear block cover to the lifter galleys
     and main bearing galley. From there, the oil follows the standard small-block Chevy split route of
     through the pushrods to the top of the engine and down to the cam, main, and rod bearings.
Something else to take into account is the fact that aluminum blocks require greater clearances than the
cast-iron blocks because aluminum grows approximately twice as much as iron. This means the major
clearances (crankshaft main and rod, camshaft, piston to bore, and so on) need to be almost double what
they would be in an iron block. We’re only talking thousandths of an inch (0.001) here, but it affects oil
consumption, the required startup procedures (to bring everything up to temperature), and component
life. The last issue is especially critical with solid-lifter cams. With the advances of hydraulic-roller
lifters, the use of solid lifters is not as common. But in some full-on racing engines that use these blocks,
the valve lash will start out very tight with the engine cold. Then, as the deck height grows from the
engine coming up to temperature, it will be at its proper valve lash. Any hard use before the engine is up
to temperature could lead to broken valvetrain parts.

Application Suggestions
In general, normally aspirated street engines below 650 hp can be supported by mid-’99-and-later stock 4/18/2006
LS1 Block Basics - Hot Rod                                                                       Page 5 of 6

LS1 aluminum blocks with just oil pressure/volume increases and basic blueprinting (honing cylinder
bores with a deck plate, ensuring the bottom end is machined correctly, and so on). Notice that the ’97
through early ’99 blocks are excluded. If you’re going to start adding power, these blocks become a
liability. They aren’t as strong as later blocks, and the oiling passage at the back of the block is
restrictive to high-horsepower applications.

Centrifugally supercharged street engines of 700 to 1,200 hp should consider the cast-iron 6.0L truck
block, with 800-plus horsepower engines using dowel-pinned steel main caps in iron blocks. In fact,
above 650 hp, steel main caps are good insurance, but the stock powdered metal caps will work fine
below this hp level on everything but nitrous’d engines. Also, on supercharged, turbocharged, or nitrous
engines above 900 hp, a main-cap girdle should be used to stabilize the caps. Head studs of 11 mm or
greater should be installed above 700 hp for maximum clamping force and used with performance
multilayer-steel head gaskets. Boosted and dry-sump-oiling-system engines should use front and rear
cover crank seals designed to handle the positive and negative crankcase pressure found in these

Ultra-high-rpm applications should seriously consider using the ’01-and-later LS6 block and possibly
dry-sump oiling. The LS6 block is suggested because the bay-to-bay breathing is much improved over
previous Gen III blocks. The production wet-sump oiling system is good, but a dry sump is better
because it can be designed to scavenge from the separate bays and eliminate this issue completely. This
is one detriment of a deep-skirted block that GM has addressed with the new Z06 Corvette LS7
engine—it is lubed by a dry-sump oiling system from the factory.

Overall, the LS1 is superior to any small-block that has come before it. GM set out to build on the
incredible legacy of this engine family, and the block design shows the company’s commitment to that
goal. Without a doubt, this engine architecture will become the benchmark performance engine for years
to come, and now you know the details behind its foundation. Enjoy the power. HRM

                                                                       The Gen III/IV V-8s use torque to
                                                                       yield bolts on the crank mains and
                                The Gen III engine was obviously cylinder heads. While the factory
When building a performance designed for electronic fuel injection uses special wrenches that
Gen III/IV V-8, you should from the get-go, so the block was automatically set these bolts at their
definitely use a deck plate     equipped with a permanently            clamping limit, recreating this in the
during the honing operation to mounted crank sensor (shown,            field requires an angle socket like
improve ring-to-bore sealing. located behind the starter on the        the one shown. The process of
Production engines are not      passenger side) and a cam-location achieving the proper clamping load
machined with a deck plate, sensor—among others. The crank is looks like this: first a low-level
though the soon-to-be-          equipped with a 24-tooth wheel to torque is achieved, then the bolts are
released LS7 will be.           tell the sensor where the engine is in twisted an additional angle in a
                                its rotation.                          torquing sequence using the angle
                                                                       socket. It’s actually a simple process
                                                                       and highly accurate.
                                Back in 1997, GM Racing
Practically every component developed a 7.0 L Gen III V-8              This illustration was created in 1991
that bolts to the Gen III/IV V- engine for the racing versions of the when the Gen III program was still
8 block does so with 8mm        C5 Corvette. The resulting engine, in its infancy. It looks somewhat like
hex-head bolts (like the oil    called the C5-R, was based on a        a Gen I small-block V-8, except for
pan bolts being used here).     special block and cylinder heads. It the many ideas on it that made it into
There are three different       featured pressed-in 4.125-inch         Gen III production, such as the deep
lengths and two diameters,      bores, minimal bay-to-bay breathing skirting on the block, front and rear 4/18/2006
LS1 Block Basics - Hot Rod                                                                                         Page 6 of 6

based on the use, but the                           passages in the bottom of the engine cover plates, structural oil pan, and
simplicity of using similar                         (it was intended for a dry-sump      braced main caps (though they are
bolts is noted. Most of the                         oiling system) and was cast from     six-bolted in production without the
bolts are torqued to 18 lb-ft,                      356 T6 aluminum, instead of the      girdle shown here). Notice there are
and many require a dab of                           production engine’s 319 T7           no head bolt holes yet—whether to
thread sealer on them as the                        aluminum. This high-tech block       go with four or five bolts per
threaded holes open up to the                       ended up being the basis for the LS7 cylinder was heavily debated before
insides of the engine.                              engine that is coming out in the C6 deciding on four per cylinder.
                                                    Z06 street car.
Car Tech Books                                                               GM Performance Parts
800.551.4754                                                                 800.577.6888                                                   

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c    Check the box to include the list of links referenced in the article. 4/18/2006

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