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Ruthless Pursuit of Power: 2008 Edition

Our In-Depth Look at the New LS3 Engine

Image:  Author
© 2007 by Hib Halverson
No use without permission, All Rights Reserved

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I turned left on I-65-north on-ramp, then buried the gas.

First: exhilaration

In seconds, I was near the top of third gear, watching traffic fly backwards when I lifted. This twenty-oh-eight, six-speed–new LS3 under the hood and optional "NPP" exhaust out back–was a freakin' rocket ship.

Then: despair.

I realized that now, my '04 Z06, good old "3Balls39", can't even keep up with a base C6. The new engine–6.2-liters, 436hp@5900 rpm–makes the standard Corvette about half-a-tenth quicker than the most aggressive Vette of just 48 months ago.

 "This sucks!" I blurted.

The GM guy with me almost got a word out.

"Dude!" I cut him off. "The motor's awesome! What sucks is you guys took only four years to make a base car quicker than my 110-lbs. lighter C5Z."

At 75 in sixth, the '08 cruised effortlessly, demonstrating once again that the wide "bandwidth" (cutting-edge performance combined with darn nice road manners) which has been a hallmark of America's Sports Car and the envy of some of the world's other great car makers since the ZR-1 years of the early-90s.

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From the outside, the LS3 case looks like last year's LS2. If you have sharp eyes, you can see the larger bore, but the other major change is deep inside.
Image:  GMPT Communications.
As we rolled towards Bowling Green and the National Corvette Museum, I reflected upon the LS3. General Motors' Generation-Three and -Four Small-Block V8s are some of the World's great engines. Don't believe it? Just ask Mercedes-Benz. When it owned Chrysler, it copied–oops–it benchmarked GM's Gen 3 Small-Block architecture then reproduced key aspects of it in its current Hemi V8.

Short Block Details

  World-class engines have robust blocks, or "cylinder cases," as powertrain engineers say. The '08 Vette's 378-cubic inch, LS3 uses the same block as the L92, a high-performance Vortec 6200 truck engine. But–don't start flaming us about SUV motors. The L92 is light, compact, reliable, durable and powerful–just the foundation a Corvette engine needs.

The LS3 case shares basics most aluminum Gen 3s and 4s have had since that engine family debuted in the 1997 Corvette: deep skirted, 319-T5 aluminum block with siamesed, cast-in-place, gray iron liners which are centrifugally-cast to increase density and allow thinner walls, long head bolts threading deep into its main bearing webs and six-bolt, steel main bearing caps. All this makes a lightweight, rigid, block structure offering good durability and reduced friction.

Chrysler borrowing from that block design for V8s in its own full-sized trucks and performance cars says much about GM's engine technology. Some might be disbelieving of the Gen 3/4 block being so inspiring to a competitor but, if you ever see the two short blocks disassembled, side-by-side on a bench; the influence will be obvious. Imitation is the best form of flattery.

There are improvements in the LS3 block. Compared to last year's six-liter, the liners have .084-in larger bores, its main bearing webs are about 20% stronger and their "windows", which enhance "bay-to-bay breathing" in the interest of oil control and reduced parasitic loss, have been somewhat enlarged.

Last Spring, we visited GMPT's World Headquarters in Pontiac, Michigan to interview John Rydzewski, Assistant Chief Engineer for Small-Block Passenger Car Engines. Rydzewski leads the team of engineers working Corvette engines and the first subject we breached was the increased block strength.

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For Corvette engine geeks, this is the Mother Ship, where most of the engine engineering is done--GM Powertrain's World Headquarters in Pontiac, Michigan.
Image:  Author
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John Rydzewski is a Corvette engine ace, both figuratively and, as he's the LS3's Assistant Chief Engineer, literally. Rydzewski worked on Small-Block as far back as 1993 and he's been ACE since 2005.
Image:  Author

"When the block is honed, the bottom of the honing tool needs clearance so it doesn't contact the block below the bore." Rydzewski told the Corvette Action Center. "Before the honing operation, the block is machined in that area to provide (hone over-travel) clearance. The resulting surface geometry has a big impact on the block structure. The hone over-travel clearance used to be machined with a 3-mm radius. With LS7, to get more strength in that area, we changed to a more gentle, 8-mm radius. That was a big durability enabler at the LS7's power level. When we got into the LS3 finite element analysis (FEA), we found our safety factor needed some improvement, so we applied what we learned about LS7's hone over-travel cut-out. We were able to increase the radius to 10-mm which was worth about a 20% improvement (compared with the LS2 and '07 L92 blocks) in the strength of the block structure in that area."

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These changes to the main bearing webs in an LS3 case (right) might not look like much, but they make a huge difference in the strength of the lower end of the block.
Image:  Steve Constable/GMPT Communications

LS3's nodular iron, rolled-fillet-journal crankshaft is similar to LS1/2/6 parts except for counter weights altered to rebalance the engine for a slightly heavier piston.

The shotpeened, powdered metal, hot-forged, steel connecting rods are the same as what was in LS2 except for a new rod bolt. Rod length remains 6.1-in. The rods are "net shape" so post-production machine work for balancing is not required. As before, they're "cracked rods" which means that, to simplify manufacturing and enhance fit between rod and cap, the big end is fractured in half rather than machined. The rods' small ends are bushed for full-floating wrist pins.

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Rods with cracked or "fracture-split" big ends are common on modern engines. The fracturing creates a unique interface that "locks" together only one way and does so very precisely. The more accurate interface ensures a uniform big end diameter and shape.
Image:  Author
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Starting with the LS2, Gen 4 V8s use a full-floating wrist pin so the rods are silicon-bronze bushed and the bushing has an oil feed groove milled into it.
Image:  Author

The new rod bolt is made of stronger material and meets the same grade 12.9 specification as do LS7 bolts. The better material allows clamp load at the rod cap interface to go from 47 kilonewtons to 50kN. The design of the rod bolt was changed, too. "An alignment feature was added to the shank of the fastener," John Rydzewski told us. "Unique threads are rolled into a short length of the shank. Compared to the standard threads, they have a larger outer diameter which provides alignment to the rod hole and they have a smaller minor diameter which provides an additional benefit of isolating much of the plastic deformation from yield to this rolled section of the fastener.

"A connecting rod bolt will have deformation along the length of the fastener which results in concentrated stress at the first engaged thread. Since unengaged bolt threads are able to freely stretch, while engaged threads are constrained by the threads in the rod, the first engaged threads are more highly stressed.

"The new Small Block bolt is similar to a 'necked-down' fastener, where the bolt stretch/deformation will be focused in a portion of the length of the bolt not near the first thread of engagement. Therefore, the concentrated stresses at the first thread of engagement will be less and the overall joint safety factor improves."

More cutting-edge technology is in the LS3 piston and ring package. The piston is a flattop design, cast with a hypereutectic, aluminum/silicon alloy containing traces of copper and nickel. The compression ratio, 10.7:1, is down slightly from 10.87:1 in '05-'07. This piston is the same as the L92's 10.5:1 unit except for a valve relief the truck piston has for additional piston-to-valve clearance required by the L92's variable cam phasing. When the relief is removed, 0.2 compression is gained but, to get higher than 10.7 requires a domed piston, the cost of which was deemed unnecessary considering LS3 met its performance and efficiency goals at 10.7:1.

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The LS3 rod bolt uses two different thread sizes and diameters to control and localize bolt stretch.
Image:  Author.
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In the early LS1 years, because of the short-skirted piston necessary in the Gen 3/4 engine family, cold piston knock was a customer pleasability issue. Since the '02 LS6, Corvette pistons have had a polymer coating on their major and minor thrust surfaces-the gray area on this LS3 piston skirt. At the end of the break-in period, a lot of the polymer and a slight amount of piston material is worn away, leaving a very consistent skirt surface, a nominal (and tight) piston-to-bore clearance and hopefully, no cold piston knock.
Image:  Steve Constable/GMPT Communications.

Ring grooves are machined with a slight upward tilt which was increased by 0.25° for '08. The top ring's tilt disappears as the ring land flexes under the pressure of combustion such that sealing and oil control are optimized. The other two grooves' tilt enhances the ability of the second ring and the oil ring to scrape oil off the cylinder walls. To further improve oil control, the LS3 piston has four holes drilled in its skirt, just below the oil ring groove downwards into its interior. These holes, two adjacent to the major thrust surface and two adjacent to the minor thrust surface, improve oil drainage from below the oil ring.

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The LS3 piston and ring package is typical of what GMPT has used since 2002 in high-performance SBV8 applications, but with more groove "tilt" and higher oil ring tension.
Image:  Author.
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Here's a "bare" LS3 piston. The hard-anodizing adjacent to the top ring groove is a durability feature. While the oil drainback notches have been in Gen 3/4 pistons for along time, new are the oil drainback holes, two each on above the major and minor thrust faces, drilled into the piston interior.
Image:  Author.
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The underside of the LS3 piston. As the piston moves down in the bore, oil is scraped off the walls by the oil ring then is "flushed" down the oil holes and into the interior of the piston.
Image:  Author.

Surfaces either side of the top ring groove are hard-anodized. The piston skirts are coated with the antifriction polymer introduced on LS6 for MY02. Interestingly, the pistons are installed with -2 micron (-.00008-in or eight hundred-thousandths of an inch) piston-to-bore "clearance"–a slight interference fit. During break-in, some of the coating wears away, leaving a nominal piston-to-bore clearance. LS3 pistons use new wrist pins having tapered inside diameters, an idea straight from the C5R race program and which reduces pin weight with no loss in strength.

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The top ring is the most critical part of compression sealing and, in an LS3, it's a pretty trick part with one of the tricks being a slight twist to the ring.
Image:  Author.
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With the rings in simulated position on a piston, you can easily see the hook-like, Napier-faced second ring. "Napier rings" are much better at scrapping oil off the cylinder walls as the piston moves down and that's the reason GM upgraded to them for 2002.
Image:  Author.

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Here's the meat-and-potatoes of the Corvette's new, 436hp engine, the cylinder head casting. It also might be (see sidebar) the head used on the supercharged 6.2 we'll see in 2009.
Image:  GMPT Communications
Oil control at high rpm has been a challenge with Gen 3/4 engines. Since 1997, to that end, GM has tried several combinations of crankcase ventilation systems and ring tension. While, for '08, the PCV caries over from LS2; the ring package has, once again, been changed. The top ring is still moly-faced steel and "coin twisted," which means its shape in side view is slightly conical to improve the ring's sealing when under combustion pressure. The second ring remains cast iron with the "Napier" face introduced in MY02 and they both are 1.5-mm. wide with the same tension as before. The oil ring is still three-piece, two rails and an expander, however, to improve oil control, for '08, its tension was increased.

Major Cylinder Head Evolution

If there's anything GM Powertrain knows well, it's cylinder heads and air flow. GMPT's "ruthless pursuit of power" has paid-off in four different Vette heads since MY97: the original LS1 head, those for LS2 and LS6, the super-trick LS7 head and, now, the LS3.

Like the block design, the Gen 3 SBV8 head was of interest to Chrysler when it was designing its Hemi. While it has different combustion chamber a second spark plug, a Hemi's head borrows from the LS1 casting.

The high-performance, L92 version debuted in 2007 GMC Yukon XLs and Denalis (380hp) and Cadillac Escalades (403hp) and was the source of the casting used for the LS3 head assembly. It's key improvement over the LS1 and LS2/LS6 heads is revision of the intake and exhaust port shapes, volumes and locations. Those changes were influenced by the '06 Z06. In fact, the L92 head was the "first" LS7 head. Part way through development, when the goal was raised to 500hp, that head was set aside and development began on a second, more aggressive design which eventually went on the C6Z's engine.

Later, when a high-performance, 6.2 was needed for premium SUVs; Powertrain put that first LS7 head back on the front burner and, after more development, it went to production for the L92. Shortly thereafter, when the upgrade program for the base engine in America's Sports Car was initiated, GMPT took the L92 casting, added some parts unique to Corvette's performance envelope and used it on the LS3.

While this new head is not a "clean-sheet-of-paper" design, it is a major evolution in Gen 3/4 cylinder head architecture and its effect on performance is profound. There were a multitude of changes which we'll discuss in detail and, for this part of our GMPT visit, the Design Responsibility Engineer (DRE) for Small-Block Cylinder Heads, Lou Oniga, joined John Rydzewski. A "DRE" is a key person on any project at GM. "The buck stops with the DRE," Oniga told us. "If anything goes wrong with their part, it is their responsibility to make it good–casting, machining, assembly, testing, drawing, dimensioning, validation, or field issues, etc. It is the DRE who is responsible. No one else! Humans sometimes make mistakes. That is why most DRE's you meet are such a strange lot. We always worry–we always are concerned that everything we do is as close to perfect as possible."

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ACE Rydzewski and DRE, Lou Oniga, discuss the LS3 head design in our May 2007 interview.
Image:  Author
The CAC staff hopes there are many more DREs like Lou Oniga working on the Corvette.

The most noticeable feature of this head is vastly different intake port location and geometry. The change was inspired by cylinder head work Mike Chapman, an under-the-radar type with a near-mythical reputation in the racing head business, did for the C5-R engine program Katech, Inc. ran for GM Racing from 1997 to 2004.

Lou Oniga takes it from here, "Based on Chapman's airflow development work, we went to a large, square intake port and did away with the 'cathedral' port we had in the older (LS1/2/6) head. The numbers say what we have now flows better than the cathedral port."

"A key enabler of this," John Rydzewski pointed out, "is moving the pushrod over. Now we had a bigger space, so we moved the port up, gave it a straight-on approach, made it larger, wider, with less turns and have less bosses in the way of the flow path. The result is a huge improvement in performance."

This new head was going on an engine having 500-cc more displacement than the one for which the previous Corvette head was designed so, not only was the shape of the ports changed dramatically but their volume was increased. Just how much larger are the ports? Lou Oniga whipped-out his little black book of head information and told us that LS2 port volumes were: 210cc for intakes and 75 cc for exhausts. LS3 intakes are 257cc and exhausts are 86cc.

To compliment larger ports, LS3s have bigger valves. The intake diameter is 55- mm (2.165") the exhaust is 40.4-mm (1.59"). Larger valves forced a 2-mm (.078") increase in valve center distance because, on this head for durability reasons, the "valve bridge"–cylinder head structure between the valves–needed to meet a minimum width whereas, with the other most recent head design for the LS7, there's no bridge at all and the valve seats are "siamesed."

In another example of aftermarket high-performance and racing processes migrating to production applications, back in 1998, GM Powertrain began making Gen 3/4 heads with multi-angle valve seats and faces. The LS3 head continues that with 30-45-60-degree multi-angle finishing on the seats and a 45° angle on the valve faces.

The "short-turn" or "short-side" radius in the intake port is the holy grail of cylinder head airflow. It is where the floor of the intake port turns downward to the area of the valve seat closest to the port entry. There are differing opinions amongst cylinder head experts about some issues, but one upon which they all agree is the importance of the short-turn radius.

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These sectioned L92/LS3 (left) and LS2/6 (right) heads show the vast difference in intake port design. You can see how the earlier intake port got the name "cathedral port" 634.16) The '08 LS3 head's lower, wider intake port, exists mainly for improved air flow but also to make room below the port for hardware used by GM's active fuel management (AFM) cylinder deactivation system.
Image:  Author.
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How did GM "made room" for the wider LS3 intake port? They moved the intake pushrod sideways.
Image:  Author.
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Flow-wise, the LS3 intake port pulls ahead of the LS3/LS6 port almost at valve opening.
Image:  GMPT Communications.
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Look at these saw-cut sections and you can see why the new head flows better. The key enablers are 1) flat port floor, 2) improved short-side radius and 3) shorter distance the intake air flows around the short side radius.
Image:  Author.
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a) A closer look at the LS2/6 head's short-side radius area. The radius is not that sharp but the curved area is quite large and the port floor is inclined
Image:  Author.

b) A similar view of the L92/LS3 port shows a radius that is actually slightly tighter but the critical area of the port floor curving down to the valve is actually less. The net sum is improved intake flow. Not the larger "cavity" beneath the intake port entry. That's the larger space needed by the AFM hardware.
Image:  Author.
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Both valve seats get a three-angle "valve job".
Image:  Author.

"It's incredible," Oniga went on, "how much effort we put into the short-turn radius. Just a few thousandths of an inch change can affect airflow significantly–as much as 7-10 grams per second, so that's where we focused a lot of attention.

"We took the UG model of the Chapman-derived racing ports," Oniga continued, " which were fully CNC-machined, sent it to our pattern shop and they made a flow-box, based on this geometry."

"UG" is "Uni-Graphics", a high-end, 3D modeling, software application. A "flow box" is a plastic model of an individual cylinder head port from port entry or exit all the way to the valve seat.

"Then, we took these flow boxes and we flowed them, made modifications, and flowed them again, repeating this process multiple times. Next we digitized the port shapes and sent the resulting models to our foundry to manufacture a representative casting. Besides the optimized port shapes and size, metal shrinkage, manufacturing requirements, parting lines, even the coarseness of the (core) sand, all affect airflow. It took 15 iterations of the LS3 intake and exhaust ports to get the airflow to where it is, today. That was rather stressful."

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The LS3 intake port's floor is flat and smooth, all the way to the start of the short-side radius.
Image:  Author.
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Here's the view of the short-side radius from the piston top. Again, the port floor is smooth. The radius, itself, is actually a bit tighter than the previous head but the curved area is smaller. The net result is a better-flowing port.
Image:  Author.

 Typically," John Rydzewski interjected, "we do a lot more analysis nowadays, but to get that extra few percent we sometimes have to do it the old-fashioned way."

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The section on the right is the LS3 intake port. Note how smooth it is compared to the LS2/6 section at left. That is the benefit of the finer core sand.
Image:  Author
"Our analysis tools are getting more sophisticated with each passing generation of cylinder head." Oniga continued. "Computer software tools such as GT Power, Uni-Graphics, CFD (computational fluid dynamics) and NASTRAN (software designed and licensed by NASA to private companies) are necessary tools of the development process" "but there's a human touch needed as well. We'd take development heads to the Warren airflow room. There's a gentleman working there named 'Dave Suminski.' He's a wizard. All he does is flow heads. He analyzes the flow data and makes subtle modifications to the port sets to optimize the air flow to (meet) our desired number. Dave is very good. He's from the old school of porting, polishing and flow testing. We'd take his input, then go back and make additional samples then, flow them again–fifteen times–until we finally got what we wanted. We really sweated the details, right down to the last 2 grams per second (of air flow), which are within the measurement capability of the equipment utilized.

"We wanted to create a port design that provided the flow numbers required for the desired horsepower, but that could also be reproduced in a mass production foundry on a day-to-day basis .

"We made sure casting shrink rates (of the aluminum as it cools) was as accurate as possible. We changed an aspect of casting technology, too. We use a different foundry sand on both the intake and the exhaust ports. We went to a finer silica sand so the inside of the ports are smoother. Many cylinder head experts will state that surface finish does not affect airflow. I have conclusive and repeatable data that, for this particular head, significant flow improvements came from changing to a finer sand."

The exhaust port in the new head, also, benefited from GM's ruthless pursuit of power. The port roof was raised slightly and the floor was lowered slightly which increased cross-sectional area and port volume. The short-turn radius is not as important in an exhaust port as it is in an intake, but flow still benefited somewhat from its being recontoured. To further improve flow, the valve guide boss was recontoured and the port roof just upstream of the valve was smoothed. Lastly, exhaust flow also benefitted from the finer core sand.

In spite of all that, the exhaust port didn't change near as much as did the intake because one thing GM didn't want to do was effect a practical reduction exhaust port cooling jacket volume. It was imperative that the head have good cooling around the exhaust port. Nevertheless, the port changed enough that a new exhaust manifold with revised shape at its port entries was required.

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The LS3 exhaust port's flow also surpasses that of the old head.
Image:  Author.
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To make the LS3 exhaust (left) better some of the same changes made to the intakes were employed: enhanced short side radius, smoother port walls and increased port height and width.
Image:  Author.

The combustion chamber in the LS3 head changed from what was used in the LS2 and LS6. The chamber is shaped differently and it's a little larger. The change in shape is the addition of a "bulge" in the chamber wall, on the opposite side of the intake valve from the short side radius.

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While the spark plug location remained the same, just about everything else in the L92/LS3 combustion chamber changed. The shape is quite different, the valves are larger and the valve centers are 2-mm father apart.
Image:  Author.
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The biggest change in the LS3 combustion chamber was the area outlined in red. That change improved the chamber's tumble characteristics and that enhanced combustion efficiency.
Image:  Author.

The best combustion quality occurs when the air fuel mixture in the chamber is distributed uniformly, or is "homogenous", throughout the chamber. The process of becoming homogenous, or as close to it as possible, occurs in the latter stage of the intake valve event and continues once the valve is closed and the piston starts upward. Not only does the upward piston movement compress the air-fuel mix but it also causes it to swirl and tumble and that further mixes it up making it more homogenous. The LS2/LS6 chamber had great swirl but not very good tumble. The air fuel mix needs to be doing both if the goal is homogenity right when the spark comes.

The bulge in the LS3 chamber exists solely to get the air-fuel mix to tumble more as the piston nears the point at which the spark lights that mixture. The bulge is also responsible for a slight increase in chamber volume, from 64.75 cc. on LS2 to 68.7 cc . on LS3, and that is part of the small compression loss compared to LS2.

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Lou Oniga is a 22-year, veteran, GM Powertrain engineer who's been the DRE for Small-Block V8 heads since 2001.
Image:  Author
 "The flow numbers," an understandably proud Lou Oniga told us, summarizing the new head, "are (average) 17% improvement on the intake and 6.2% on the exhaust."

"That's very impressive." Rydzewski continued. "(The intake port has) more of a straight path, right down to the valve and that was very important to air flow. Lou did a good job, taking what the race guys came up with then refining that–tweaking it in our airflow facilities–to get where it is with LS3. It's a great high-volume cylinder head design which performs very well."

Stout Head Structure

The LS3 head has more than just great airflow. Since the big change in port configuration would drive changes in the core boxes used to cast the head, Powertrain took the opportunity to alter the head's structure for improved reliability/durability.

"We did extensive finite element analysis (FEA)", Lou Oniga stated. "We have an outstanding analysis group which was able to take our Unigraphics models and then utilize NASTRAN formulae for very detailed FEA."

Computer analysis and simulation software has become indispensable to engineering not only at General Motors, but industry-wide. Powertrain utilizes this software to perform analysis of its designs and to simulate engine tests, such as GED (Global Engine Test Durability Cycle), GTEC (General Engine Thermal Cycle) and PTED (Power train Engine Durability) all severe durability test schedules simulating 150,000 miles of abuse by a 95th percentile customer.

Obviously, such software tools require lots of computer power to run and, thus, are very costly but the costs are recovered many times over because analysis and simulation allows GM to bring its products to market faster. Some call this "from art to part", meaning that parts can make it from math art to production with less prototypes and less physical testing, but we emphasize: never to the point of no testing.

"We discovered that the exhaust manifolds have a tendency to grow significantly during the first thermal cycle and distort the end faces of the cylinder head," Oniga continued. "The intake side expands very little but the exhaust face grows significantly.

"Because of this distortion, we took the cup plugs out of the ends of the head. People believe those are 'freeze plugs,' but they're not. The hole’s primary purpose is to support the water jacket core inside the cylinder head so when molten aluminum flows into the mold, the water jacket core doesn't float or move around while the casting solidifies.

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By removing the cup plug, the head structure at the edges of the exhaust manifold flanges were strengthened. That strength reduced the impact the exhaust manifold's thermal cycling had on the head structure.
Image:  Author
Examine earlier heads other than for LS7s and you'll see the bores into which these plugs go are pretty good sized–about one inch diameter. The structure of the head in the areas adjacent to the exhaust manifold ends is not as stiff with those holes in it as it would be if those surfaces were continuous.

"We developed a new way to support the water jacket core through the deck face, locking it to the combustion chamber portion of the dies used to form the casting," Lou Oniga stated. "We got rid of the holes, which eliminates a potential leak path, eliminates a part–always good from a cost standpoint–and strengthens the structure of the cylinder head.

"We were able to run this head through multiple, detailed FEA analyses. We, improved the internal strength of the head with a more robust water jacket core. It has what I call the 'super jacket' which has excellent strength and a higher safety factor, but doesn't use much more metal internally than the current LS2 head.

"The valve seats are also more robust. The material still in production (at the time of this interview, mid-May '07) is a powdered metal, tool steel with some molybdenum-disulfide and traces of other metals.

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This is a killer, LS3, copper-infiltrated exhaust valve seat. The copper mixed in with the steel give it a sort of platinum appearance.
Image:  Author
"The Small-Block does not have water flowing completely around the valve seat inserts. When things get extra hot, you want fast heat transfer away from the valves and valve seats and into the water jacket. Because we did not have the luxury of adding water jacket cavities completely around the valves, we decided to employ a copper-infiltrated valve seat insert.

"The supplier, Federal-Mogul, takes a powdered metal blank and puts a copper cap over it. They run it though an oven, the copper melts and wicks into the voids of the powdered metal. Powdered metal has microscopic cavities into which this copper infiltrates. The main difference between the two inserts is the exhausts have more copper because they run hotter. The intakes can get by with less because they run cooler due to fuel spray and cool air flowing past them.

"Heat transfer increased significantly. We were able to get 4-6% faster heat transfer, out of the valves, though the seats and into the water jacket. Also, the added copper is easier to machine, so cutting tools used to machine them last longer.

"We invested in new, capital equipment. Obviously, because the valves are larger, we had to buy several new pieces of transfer equipment to cut the valve seats as well as other unique features. This allowed simultaneous engineering with the manufacturing engineering group permitting improvements in machining technology and increased accuracy."

The new machining processes made practical more stringent specifications for the surface quality of the head's deck and exhaust manifold faces. In North America, the American National Standards (ASNI) Institute sets standards for geometric dimensioning and tolerancing (GD&T) and ASNI recently adopted tighter finish and flatness requirements, specifically: Rz (average roughness), Rmax (maximum roughness), and Wt (maximum peak to minimum peak of the roughness range), all of which are surface finish benchmarks used by the metal working industries.

The application of new machining processes improved sealing between head, gasket and block along with that between head, exhaust gasket and exhaust manifold. We should point out, however, that we're "splittin' hairs," here, because the quality of these surfaces on previous engines was already very good. Apparently, they now are even better, but the improvement is incremental–we're talking less than a thousandth of an inch.

"The surface finish achieved is not unlike the surface of a compact disc–it is that smooth," Lou Oniga added. "This permits a 'designed-in' amount of relative sliding movement between the block, gasket, and cylinder head, keeping gasket wear and tear at a minimum during the millions of thermal cycles which will occur during the engine's life."

The reason for that seemingly small but important change is, as Oniga told us, "Deck and exhaust face surface finish and flatness are very critical when using modern, multi-layer, steel (MLS) cylinder head and exhaust manifold gaskets."

In conjunction with the surface finish enhancements, through 2006 and the first half of '07, Powertrain researched head gasket designs then released a new, 5-layer gasket for LS3–as opposed to a 3-layer gasket on LS2.

Serious engine sealing geeks work at GMPT and, over lunch, they talk about "gap amplitude." Combustion pressure pushes the head up. No matter how much clamp load the head bolts provide; that head wants to lift. The lift is called "gap amplitude" and the cylinder head gasket has to be able to fill or conform to it. If the lift exceeds the gasket's conformal capability; you get a leak. Even a short duration, small leak and exhaust gases start blowing by or coolant leaks. The LS3 gasket's two extra layers offer better sealing.

Another requirement for LS3 was the same or better oil flow though the head's oil drain cavity. The increase in port size took a bite out of the existing oil drain volume. The Small-Block team didn't want to shrink that passage, so they changed its shape to keep the same surface area and that made yet another change in the head's architecture.

Finally the rocker cover rail has a bigger sealing land. There's more material all the way around it. With FEA studies, GMPT learned the head was twisting a little. Bulking-up the sealing land stiffened the rocker cover area and provided a more robust seal.

Cam and Valvetrain

The Gen 3/4 valvetrain continues to evolve with previous Z06 features appearing in base engines. The LS3 camshaft is based on the one used in the C5Z's groundbreaking, LS6. Its intake lobe comes from the '02-'04, 405-horse cam. The exhaust profile is from the 385-horse LS6 of  2001 and the LS2 of '05-'07. For LS3, in order to reduce overlap, lobe separation was increased a degree over the LS2 cam. The net sum of all this was more intake airflow and a smoother idle.

Camshaft Profile, Intake Comparison

(All lift figures are valve lift)

year RPO

 

int.

lift

int. dur.

at .004

int. dur.

at .050

int. open

at .004

in. close

at .004

in. open

at .050

in. close

at .050

int.

CL

int.

area

int. area

increase

MY01 LS6

 

13.34 mm

.525 in

270°

204°

BTDC

81°

ABDC

18

ATDC

42

ABDC

118°

ATDC

1862.9

mm/deg.

n/a

MY02 LS6

 

14.01 mm

.551 in

267°

204°

BTDC

80°

ABDC

19°

ATDC

43

ABDC

120°

ATDC

1936.9

mm/deg.

4%

MY05 LS2

 

13.34 mm

.525 in

270°

204°

BTDC

81°

ABDC

18°

ATDC

42

ABDC

118°

ATDC

1862.9

mm/deg.

0

MY06 LS7

15.06 mm

.593 in

276°

210°

BTDC

88°

ABDC

18°

ATDC

48°

ABDC

122°

ATDC

2166.4 mm/deg.

16%

MY08 LS3

 

14.01 mm

.551 in

267°

204°

BTDC

80°

ABDC

19°

ATDC

43

ABDC

120°

ATDC

1936.9

mm/deg.

4%

Camshaft Profile, Exhaust Comparison

(All lift figures are valve lift)

year RPO

exh.

lift

exh. dur.

at. .004

exh. dur.

.050

ex. open

.004

ex. close

.004

ex. open

.050

ex. close

.050

exh.

CL

exh.

area

ex. area

change

MY01 LS6

 

13.33 mm

.525 in

275°

211°

65°

BBDC

30°

ATDC

37

BBDC

6

BTDC

114°

BTDC

1914.6

mm/deg.

n/a

MY02 LS6

 

13.91 mm

.547 in

282°

218°

69°

BBDC

33°

ATDC

42

BBDC

4

BTDC

115°

BTDC

2046.6

mm/deg.

8%

MY05 LS2

 

13.33 mm

.525 in

275°

211°

65°

BBDC

30°

ATDC

37

BBDC

6

BTDC

114°

BTDC

1914.6

mm/deg.

0

MY06 LS7

14.95 mm

.589 in

296°

230°

81°

BBDC

35°

ATDC

53

BBDC

3

BTDC

119°

BTDC

2359.4 mm/deg.

23%

MY08 LS3

 

13.33 mm

.525 in

275°

211°

66°

BBDC

29°

ATDC

38

BBDC

7

BTDC

115°

BTDC

1914.6

mm/deg.

0

The mix of lobe profiles, also, means there are two different base circles, 19-mm for the intake and 19.3-mm for the exhaust. Because of the different base circles, to keep valve train geometry optimized, two different valve lengths are used in the LS3 with intakes 0.6-mm. longer than exhausts.

Click image for larger view

The lift curves for the LS3 camshaft.
Drawing:  GMPT Communications
We interviewed valvetrain Design Release Engineer, Jim Hicks several times in recent years for stories on LS1, 2 and 6 and he told us, "All our cams (prior to LS6) had the same base circle radius. We had a problem, if we wanted higher lifts: the nose of the cam would approach the same diameter as the cam bearing journals or even exceed them.

"Obviously, that means you can’t install the cam in the engine–little bit of a problem. Your only alternatives are to increase rocker arm ratio, which we weren’t going to do (for this engine), or reduce the base circle radius."

The first base circle reduction, for the ’01 LS6, did not require a change in any other valvetrain part, however, the 405-horse cam for '02 was a different story as was the LS3's intake lobe, which uses the same profile.

"I wasn’t comfortable reducing base circle that much," Hicks told us, "without compensating for it somehow, because the position of the plunger within the hydraulic lifter is not optimal any more–you’re too high in the lifter.

"There are different ways to correct the geometry. The one we selected to minimize the impact on our manufacturing operations was to increase the length of the valve. The valves in the 02 LS6 and intake in the LS3 are 0.6-mm. longer than the valves in other engines."

Another new feature of the LS3 valve gear is offset intake rocker arms. Similar in concept to those used for the current Z06's LS7, they have a 1.7:1 ratio. The offset is .246-in. and exists so the pushrod could be moved sideways about a quarter of an inch, allowing those wider intake ports.

Click image for larger view

Bird's eye view of the L92/LS3 rocker arm assembly. The offset intake rocker is obvious. What is not be so obvious is the more robust rocker cover seal surface.
Image:  Author.
Click image for larger view

The LS3 intake rocker's offset is nearly a quarter of an inch. The material remains investment-cast steel. The rockers are typical of O.E.s in that they have roller trunnions but not roller tips. Roller tips are really not necessary and are used in aftermarket aluminum rockers because its easier to add a roller rather than some other method of hardening the valve tip.
Image:  Author.

Click image for larger view

The LS3 intake valve (right) compared to the LS2 unit. The new part has a larger, polished head and a hollow stem.
Image:  Steve Constable/GMPT Communications.
Taking another page from the Z06 engine book, the LS3 intake valve, because its larger diameter increases mass, now has a hollow stem to get weight back down to where the valvetrain is stable to the same, 6600 rpm rev limiter used on the LS2. The  LS3 valve spring used is the "double-shotpeened," Gen 3/4 high-performance unit, originally developed for the LS6 and used in LS2.

Intake and Exhaust

The Corvette intake manifold has, once again, been changed. One reason is the intake port floor in the head is much higher and the port is wider. That, alone, drove  development of a new intake.

Gen 3s all used a glass-reinforced Nylon-6,6 intake which was manufactured using the lost core process. In 2005, for the Vette's first Gen 4, the LS2, GM switched to a different material, Nylon-6, and went to a vibration-welding manufacturing process. For the LS3, Powertrain decided to go back to a one-piece, lost-core, intake.

"Since the ports moved up and their shape changed," John Rydzewski stated, "we needed a new intake. It's still made of Nylon-6 but it's now done with the lost core process. The manifold is specific to passenger car applications that use this cylinder head.

"A vibration-welded intake has different shells. One port can be a combination of an upper portion and a bottom portion with the runners welded together on the side. It's a pretty good seam, but there might be a little crosstalk (port-to-port leakage) which can rob you of some power. We had seen that in some applications, so we went to a lost-core intake.

Click image for larger view

The LS3 intake returns to lost core manufacturing. This is the bare intake. It is assembled with injectors and fuel rails by its supplier before being shipped to a GM engine plant.
Image:  Steve Constable/GMPT Communications.
"We also reshaped it for better flow. Yoon Lee, who's been on the program for a few years, did the development. Compared to LS2, he reduced restriction by 2-3% at 13.5mm lift. It's just a smoother path, right down to the head. There's some extra structure–some different type of webbing on the bottom of the manifold–to stiffen it up. We, also, went to metallic compression limiters (inside the manifold bolt bosses) vs. the previous composite compression limiters. You've got the long columns and, with time, composites–if you do over-tighten–can creep."

"Creep" is a bit of a misnomer because it implies that the manifold, as a unit, moves. Better terms might be "extrude" or "deform". If you tighten the intake manifold bolts on a plastic intake, over time and especially if the bolts are over-tightened, the plastic may extrude, radially, away from where the fastener load is applied.

For long-term durability," Rydzewski added, "we don't want any creep in our manifold, so we're applying 'Bill-of-Design'–more of what we learned (that metallic compression limiters in the bolt bosses eliminate creep) from other applications."

LS3's injectors come from LS7. With 30-36 more horsepower, LS7's 5-gram/sec. injectors were necessary. The throttle body carries-over from the LS2. There are no functional changes to the positive crankcase ventilation (PCV) system. The induction system ahead of the throttle body is from the Z06 but with some quarter-wave tuners added to attenuate certain frequencies of intake noise.

The exhaust manifolds are similar to the units introduced in 2005 on LS2 but have a slight change in each exhaust runner where it bolts to the head to match the revised exhaust port exits.

These manifolds were revolutionary in '05, as GM employed a new material, cast iron with higher silicon and molybdenum content, which made a stronger casting. As a result, the wall thickness of the part could be reduced by about 25% and that took 10.5 lbs out of the car. A new MLS exhaust gasket was, also, released.

Engine Controls and Bin 4 Emissions

Click image for larger view

The guts of an industrial-strength iPod? Hardly. This is the circuit board of the Corvette's E38 engine controller.
Image:  Author.
The engine control module (ECM) or "controller" as the guys who develop this stuff say, was new for 2006. Known internally as "E38, this new controller is part of GMPT's "Strategic Engine Management Complexity Reduction Initiative"–yeah, GM is like the Federal Government when it comes to thinking-up names. This program will result in only three engine management systems which share as many parts as possible.

The E38 has enhanced electronic throttle control (ETC) ability and it supports the 58x crankshaft position signals and 4x camshaft position signals which will be more common in coming years. It is a more thermally-robust design which can be mounted under the hood and close to the engine which reduces wiring harness length and complexity. It also uses connectors which meet standards set by the Electrical Wiring Component Applications Partnership (EWCAP) of the United States Council for Automotive Research (USCAR), a organization set-up by GM, Ford and Chrysler to foster the technology base of the domestic automotive industry.  

As for the deep-geek aspects of the E38: its CPU is Motorola's PowerPC. It's a 32-bit, RISC processor running at 40Mhz with 64Kb or RAM and 2 Mb of flash ROM.  The RAM nonvolatile and ignition independent and the flash EPROM, which contains the E38's calibration is nonvolatile and battery independent. E38 the carries over to the LS3 and is used on all Corvettes.

One capability enabled by the combination of the E38, LS3's improved combustion dynamics and enhanced emissions control devices, is compliance with the more stringent, Tier 2, Bin 4 exhaust emissions standard. These "bins" get tougher in a downward progression so, Bin 4 is cleaner than Bin 5. "With Bin4 emissions," John Rydzewski told us, "useful life hydrocarbon emissions are reduced by over 12% and useful life NOx emissions are reduced by over 40% compared to the LS2."

We should add that, Bin 4 emissions compliance comes with 36 more horsepower and no change in fuel economy. Plus if you order the LS3 with NPP exhaust, the darn car sounds better.

More performance, more green, less gas, better sound? Works for us!

Looks like the LS3 Team at GM Powertrain did a damn fine job.

Click image for larger view

The power and torque curves for both LS3s compared to the LS2. It's expected that the LS3 would be stronger above 3500 rpm but, the extra displacement, adds torque from idle to 3000 rpm.
Drawing:  GMPT Communications.
Click image for larger view

No Corvette engine story would be complete without a Kimble cutaway drawing. This art is beautiful.
Drawing:  David Kimble/GMPT Communications.

The Corvette Action Center would like to thank Sam Winegarden, John Rydzewski, Lou Oniga, Jim Hicks, Tom Read and Susan Garavaglia of GM Powertrain Division for their assistance with this article.

For space reasons, this story could not cover many details of the LS3 which carried-over from past engines. For more information on the LS1/2/6 engines see the following web resources:

LS1:  http://www.idavette.net/hib/ls1c.html

LS6:  http://www.idavette.net/hib/ls6/INDEX.HTM and http://www.idavette.net/hib/02ls6/index.htm

LS2:  http://www.corvetteactioncenter.com/specs/c6/2005/sequel5.html

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