High-Performance GM LS-Series Cylinder Head Guide
By David Grasso
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High-Performance GM LS-Series Cylinder Head Guide - David Grasso
INTRODUCTION
The LS1 and its subsequent siblings are among the most formidable V-8s ever made for a production car. Add in some aftermarket parts and you can have performance only previously thought available with a radical race setup or big-block-type cubic inches. Oddly enough, the impetus for the revolutionary engine was a cylinder-head design closely related to the decades-old Ford Windsor. However, since then, the original cathedral-port design from General Motors has come a long way thanks to aftermarket manufacturers. The flow capable from the production LS3/L92 heads, to say nothing of an LS7 or canted valve head, has almost single-handedly raised the bar. Even cathedral port heads now exceed 350 cfm and 900 hp naturally aspirated. Needless to say, with the power and efficiency of LS1s, they have become extremely popular among hot rodders and racers. Chapter 1 discusses the basics of this evolution.
Chapter 2 examines the Gen III and IV small-block Chevy cylinder head market, starting with the original LS1 design and progressing to the other factory cathedral port heads such as the mighty LS6, as well as the LQ9 and LM7 truck heads, before moving on to various aftermarket offerings. Each casting and design has its own distinct advantages, so it is up to you to decipher which one best suits your needs.
For example, heavier vehicles (like trucks) may be better suited for a smaller runner cathedral port head that enables more torque. As a result, the AirFlow Research 210-cc LSX Mongoose and TrickFlow GenX 205 heads may be just what you need.
Chapter 3 focuses on rectangular port cylinder heads and Chapter 4 discusses race port heads. As many know, the C5R race head, created for the GM racing program including the championship-winning C5R Corvette, birthed the rectangular port LSX heads. Since then, General Motors has released the revolutionary L92 (and later LS3/L99) head, with flow numbers unheard of in a production engine, let alone one with as-cast ports. That, of course, was followed up with the LS7 head, which boasted even better flow numbers and CNC porting, a rarity in a production engine. In the interim, and since then, the aftermarket has been doing its best to improve upon GM designs with new castings of the L92/LS3, LS7, and C5R, as well as fresh designs to eliminate the conventional inline valve setup to suit hardcore racers.
Chapter 5 discusses several supporting components, and how they relate to LS-series cylinder heads, including intake manifolds and rocker arms. There are many choices when it comes to these key components, and this chapter provides some insight into choosing the right one for your combination that matches up to your cylinder heads.
Though typical LS-series owners are reluctant to leave behind their stamped-steel factory rockers, I cover modifications that can be made to factory heads, as well as steel and aluminum roller rockers, which helps reduce friction and wear, while providing high-RPM stability.
For solid-roller and full-on race builds, special attention should be paid to the section on shaft-mount setups. Some LS-series heads can make this a bit challenging, but nothing a quality machine shop can’t handle.
Chapter 6 provides details on factory, modified factory, and aftermarket engine blocks.
The LS1 was introduced in the 1997 Corvette, sporting 5.7 liters (346 ci) of displacement, 350 hp, and 350 ft-lbs of torque. The new (Gen III) design was a radical departure from both Gen I and Gen II small-block Chevy designs, using an aluminum block with a 3.89-inch bore and 3.62-inch stroke. The head design was a close relative of the Ford Windsor’s, sporting a cathedral-shaped intake and oval exhaust ports. There were many variations on this original design, from the iron-block 4.8, 5.3, and 6.0 truck engines to the front-wheel-drive LS4. The runners and chambers varied with each application, as did output; however, all sport the same basic port shape. (Photo Courtesy General Motors)The LS1 was introduced in the 1997 Corvette, sporting 5.7 liters (346 ci) of displacement, 350 hp, and 350 ft-lbs of torque. The new (Gen III) design was a radical departure from both Gen I and Gen II small-block Chevy designs, using an aluminum block with a 3.89-inch bore and 3.62-inch stroke. The head design was a close relative of the Ford Windsor’s, sporting a cathedral-shaped intake and oval exhaust ports. There were many variations on this original design, from the iron-block 4.8, 5.3, and 6.0 truck engines to the front-wheel-drive LS4. The runners and chambers varied with each application, as did output; however, all sport the same basic port shape. (Photo Courtesy General Motors)
The LS6 engine, introduced for the 2001 Corvette Z06 model, took the cathedral port to the next level and also used a larger camshaft, higher-flowing intake manifold (adopted to all LS1s thereafter), and higher compression to make 385 hp and 385 ft-lbs. Though they both utilize the same-size (2.00 intake, 1.55 exhaust) valves, the LS6 flows some 40 to 50 cfm better while still using an as-cast finish. For 2002, GM switched cam profiles to increase output to a whopping 405 hp and 400 ft-lbs. This version was also used in the 2004 CTS-V. Photo Courtesy General Motors)The LS6 engine, introduced for the 2001 Corvette Z06 model, took the cathedral port to the next level and also used a larger camshaft, higher-flowing intake manifold (adopted to all LS1s thereafter), and higher compression to make 385 hp and 385 ft-lbs. Though they both utilize the same-size (2.00 intake, 1.55 exhaust) valves, the LS6 flows some 40 to 50 cfm better while still using an as-cast finish. For 2002, GM switched cam profiles to increase output to a whopping 405 hp and 400 ft-lbs. This version was also used in the 2004 CTS-V. Photo Courtesy General Motors)
The Gen IV platform started with the LS2 in the 2005 Corvette and GTO, though no radical departures were made from the previous Gen III until later. The LS2 had a larger 4.00-inch bore, and a few improvements to the block, but heads identical to the LS6. Using the original (2001 version) cam from the LS6, the larger-cube LS2 (364) made 400 hp and 400 ft-lbs. (Photo Courtesy General Motors)The Gen IV platform started with the LS2 in the \ 2005 Corvette and GTO, though no radical departures were made from the previous Gen III until later. The LS2 had a larger 4.00-inch bore, and a few improvements to the block, but heads identical to the LS6. Using the original (2001 version) cam from the LS6, the larger-cube LS2 (364) made 400 hp and 400 ft-lbs. (Photo Courtesy General Motors)
The Corvette C5R and C6R racing programs are largely responsible for the evolution of the Gen IV. The rectangular port C5R heads gave birth to the LS7 casting as well as the more economical L92 design. (Photo Courtesy General Motors)The Corvette C5R and C6R racing programs are largely responsible for the evolution of the Gen IV. The rectangular port C5R heads gave birth to the LS7 casting as well as the more economical L92 design. (Photo Courtesy General Motors)
The mighty LS7 produced 505 hp and 470 ft-lbs using 427 ci (7.0 liters) of displacement (just like its C5R and LS7R cousins), debuting in the 2006 Corvette Z06. With an ultra-lightweight valvetrain and rotating assembly, chock full of high-end components such as titanium connecting rods and valves, dry sump lubrication, etc., the LS7 represents the pinnacle of factory Gen IV design, including the rectangular intake port (albeit with a raised runner and CNC porting). (Photo Courtesy General Motors)The mighty LS7 produced 505 hp and 470 ft-lbs using 427 ci (7.0 liters) of displacement (just like its C5R and LS7R cousins), debuting in the 2006 Corvette Z06. With an ultra-lightweight valvetrain and rotating assembly, chock full of high-end components such as titanium connecting rods and valves, dry sump lubrication, etc., the LS7 represents the pinnacle of factory Gen IV design, including the rectangular intake port (albeit with a raised runner and CNC porting). (Photo Courtesy General Motors)
The L92 was the first Gen IV engine released in the United States, as the powerplant for the 2007 Escalade, to sport a much more economical rectangular port design that would later be the basis for nearly all Gen IVs. These heads were originally used on the L76 engine in the 2006 Holden in Australia, and then in 2008 when this model came to the United States as the Pontiac G8 GT. The high-flowing, large-runner design had mammoth valves, which easily made 361 hp and 385 ft-lbs in the detuned 6.0 G8. The L92, however, utilized a new block design with 6.2 liters (376 ci) of displacement and variable valve timing to make a conservative 403 hp and 415 ft-lbs. (Photo Courtesy General Motors)The L92 was the first Gen IV engine released in the United States, as the powerplant for the 2007 Escalade, to sport a much more economical rectangular port design that would later be the basis for nearly all Gen IVs. These heads were originally used on the L76 engine in the 2006 Holden in Australia, and then in 2008 when this model came to the United States as the Pontiac G8 GT. The high-flowing, large-runner design had mammoth valves, which easily made 361 hp and 385 ft-lbs in the detuned 6.0 G8. The L92, however, utilized a new block design with 6.2 liters (376 ci) of displacement and variable valve timing to make a conservative 403 hp and 415 ft-lbs. (Photo Courtesy General Motors)
The LS3 in the 2008 Corvette used a lower profile intake manifold and a larger camshaft to make 436 hp and 428 ft-lbs. The valvetrain was also slightly revised for the higher-revving cam. Similar versions were used in the 2009 G8 GXP and the 2010 Camaro SS, making roughly the same output. The exception being the VVT-equipped L99 that GM paired with an automatic transmission in the Camaro SS, which made 400 hp and 410 ft-lbs. Its camshaft was a much tamer design, made to provide longevity to the Active Fuel Management system (also known as Displacement on Demand), just like the G8 GT’s L76. (Photo Courtesy General Motors)The LS3 in the 2008 Corvette used a lower profile intake manifold and a larger camshaft to make 436 hp and 428 ft-lbs. The valvetrain was also slightly revised for the higher-revving cam. Similar versions were used in the 2009 G8 GXP and the 2010 Camaro SS, making roughly the same output. The exception being the VVT-equipped L99 that GM paired with an automatic transmission in the Camaro SS, which made 400 hp and 410 ft-lbs. Its camshaft was a much tamer design, made to provide longevity to the Active Fuel Management system (also known as Displacement on Demand), just like the G8 GT’s L76. (Photo Courtesy General Motors)
The supercharged LS9, released in the 2009 Corvette ZR1, took the LS3 design to the next level, featuring a stronger alloy and less-porous casting method. Its heads mated to the block with larger-diameter head bolts for better clamping. A number of other improvements, including CNC porting and titanium valves, helped the supercharged 6.2 push out 638 hp and 604 ft-lbs. The LSA bridged the gap between the LS3 and the LS9, making a more conservative 556 hp and 551 ft-lbs, while debuting in the 2009 Cadillac CTS-V. The LSA uses a smaller (1.9 liters) supercharger to force air through a more durable casting than the factory LS3, though most of the valvetrain (except for the camshaft) is identical. (Photo Courtesy General Motors)The supercharged LS9, released in the 2009 Corvette ZR1, took the LS3 design to the next level, featuring a stronger alloy and less-porous casting method. Its heads mated to the block with larger-diameter head bolts for better clamping. A number of other improvements, including CNC porting and titanium valves, helped the supercharged 6.2 push out 638 hp and 604 ft-lbs. The LSA bridged the gap between the LS3 and the LS9, making a more conservative 556 hp and 551 ft-lbs, while debuting in the 2009 Cadillac CTS-V. The LSA uses a smaller (1.9 liters) supercharger to force air through a more durable casting than the factory LS3, though most of the valvetrain (except for the camshaft) is identical. (Photo Courtesy General Motors)
CHAPTER 1
THE BASICS
Before I get into the the meat of the book—the spec charts—there are a few things you need to know. They include information on converting from a cathedral port to a rectangular port, some thoughts on the merits of cathedral versus rectangular ports, and a bit of cylinder head theory.
The intake manifold is the most important element in swapping from a cathedral to a rectangular port head. To match the runners, this factory LS3 (PN 12610434) or an L76 manifold are the most popular. It is important to note that there are some minor differences between the L76 and LS3 intakes, such as a screw-in MAP sensor instead of the Gen III-style clip-in; though none are of any real consequence to swapping over. These factory manifolds come as shown here with a 90-mm electronic throttle body, injectors, fuel rails, and gaskets. (Photo Courtesy General Motors)The intake manifold is the most important element in swapping from a cathedral to a rectangular port head. To match the runners, this factory LS3 (PN 12610434) or an L76 manifold are the most popular. It is important to note that there are some minor differences between the L76 and LS3 intakes, such as a screw-in MAP sensor instead of the Gen III-style clip-in; though none are of any real consequence to swapping over. These factory manifolds come as shown here with a 90-mm electronic throttle body, injectors, fuel rails, and gaskets. (Photo Courtesy General Motors)
Converting from Cathedral to Rectangular Port
Since the factory L92 cylinder heads were released, one of the hottest topics has been how to convert older (cathedral port) LS-series combinations. Thankfully it is a pretty simple head and intake swap, which lends itself well to fairly high horsepower combinations on a modest budget. And since all LS blocks have the identical (four-per-cylinder)