There's a fantastic article on the LS7 at Camaro Home Page.com:
READ ORIGINAL ARTICLE HERE
PART ONE:
Ruthless Pursuit of Power: Lucky Seven Edition
The Mystique of the Z/28's 7-Liter, 7000-RPM, LS7
by Hib Halverson, Content Director
Oops! Darn those pesky leaks! Image: Various Web Locations.
In 2012, Camaro Nation got a nice Christmas present when the "VIN Card" for 2014 leaked out of GM. It listed "LS7", the seven-liter engine formerly used in Corvette C6 Z06es, as a regular production option for the Camaro in '14.
Of course, official GM denied the leak was accurate. As Chevrolet's spokesperson for everything Camaro, Monte Doran, told us right at the end of 2012, "It is our policy to not discuss future products, so I cannot comment on plans for the 2014 Camaro. I can tell you that a very early draft of our 2014 VIN card was leaked online. It was a preliminary version that included both inaccurate and incomplete information."
Yeah, right.
Three months later, at the New York Auto Show, Chevrolet announced a limited run of Camaro Z/28s powered by LS7 427s.
2014 Camaro Z/28. Image: GM Communications
This car ain't nothin' but a trackrat's hot rod. You'll get the 427, the Camaro version of which is estimated to produce 500-horsepower, six-speed manual, the iron-case drive axle, coolers, a suspension more aggressive than a ZL1's along with the carbon brakes once used on C6 Vette ZR1s and Z06/Z07s. What you won't get is, also, interesting. These 427 Camaros are serious track cars with no acoustic insulation or trunk carpet, no power seats, no HIDs, no fog lamps, a single speaker sound system and optional air conditioning.
The Z/28's 500-hp surprise. Image: GM Communications
The Milestone LS7
I think that big, thumping 427 is the high water mark for Camaro engines. The ZL1 folks probably wanna slap me silly for saying that, but, the fact remains: LSA, for all its technology, still needs a supercharger to make its 580 horses. Without boost, it wouldn't get much beyond the LS3's 426.
About 150 of the LSA's 580-hp come from this–GM's interpretation of the Eaton, R1900, Twin-Vortices Series, Roots supercharger.
Image: Author.
The 427 is an amazing piece of work: fat torque curve, 500-hp, normally-aspirated, at 6300-RPM and a 7100 rev limit. There's really cool stuff in that engine–titanium rods and intake valves, 11.0:1 compression, CNC-machined heads and a 7000-RPM valvetrain. The LS7's specific output (power÷displacement) is 1.18 and its power density (power÷weight) is 1.12. At this writing, seven years after the engine debuted in 2006, both are high marks for a normally-aspirated, production V8 made in the Western Hemisphere. Such performance makes for a mystique about that unboosted, stump-pulling, high-revving V8 which the supercharged 6.2 in the ZL1 lacks. So–while I appreciate the LSA, to me; LS7's case is more compelling.
The obligatory, but always stunning, Kimble cutaway shows the guts of a Corvette LS7. The Camaro version looks the same except for having black beauty covers and different exhaust manifolds. Image: David Kimble for GM Powertrain.
GM Powertrain Division (GMPT) likely objects to my "high water mark" statement citing the specs of the direct-injected, 450-hp, 6.2L V8 which will power the 2014 Corvette Stingray. No doubt, the "LT1", the first example of the Fifth-Generation Small-Block V8, is an outstanding technology showcase, but the fact remains: a 427 in a production Camaro is a very rare, it's only happened twice in the last 50 years. After the 2014 Z/28 build, you'll likely not see another unblown V8 making more than 450-horses.
Set the Wayback Machine for 1969.
Some say, "History repeats itself." The LS7 channeled a legendary engine of the past, the ZL1, all-aluminum, 427 developed for the '69 Camaro. Both are big-bore, pushrod V8s, influenced by Chevrolet's efforts in motorsports. The ZL1 was a race engine detuned and configured for street use. Some might say the LS7 is similar: Corvette C5-R race engine technology adapted to a production application with compromises for drivability, emissions compliance and fuel economy.
When it comes to Chevy aluminum block 427s, how far has technology marched? A ZL1 made about 560-horses at 6800-RPM. When tested with 1960s dynamometer procedures, the LS7 produces about 550-hp@6300 RPM, but has a fatter torque curve, weighs less, has far lower exhaust emissions and gets much better gas mileage. Further, it has better reliability/durability, requires less maintenance and is a lot nicer to drive. In today's money, a ZL1 cost about thirty large. You can buy an LS7 for a little over half that. The old ZL1 was installed in two Vettes, 69 Camaros and, later, sold over the counter, with somewhere between 90 and 300 produced. To date, around 9000 LS7s have been hand-built at GM's Wixom, Michigan, Performance Build Center (PBC). They've used in '06-'13 Vettes, sold as crate engines and, now, used in a Camaro. Seems we've come far in nearly half-a-century.
The 1969 Camaro all-aluminum 427.
Image: GM Powertrain.
The 2014 Camaro all-aluminum 427.
Image: GM Powertrain.
LS7 History Book
Ok–reset the Wayback to the early-'00s. In the American LeMans Series and at the 24 Hours of Le Mans, Corvette Racing had been eating everyone's lunch. Its all-conquering C5-Rs were powered by Katech-built, 427s. Based on production, LS1 architecture, they used a special cylinder block with larger-than-stock bore and stroke, racing valve gear, different cylinder heads, a motorsports-specific EFI and an intake restrictor. Katech's C5-R 427s made about 600 horses at 6200-RPM.
Meanwhile, in the Summer of 2002, over at GM Powertrain in Pontiac, where development of production hardware took place, the Small Block team, researching an LS6 successor, was experimenting with a 6.4-liter (390-cubic inch) V8 of about 450-hp. The 2005 Corvette was in development and they were looking at this "six-four" as what might power the next Z06, due a year later. During the design of the 6.4's cylinder head, Katech's C5-R engines were an influence. The most noticeable feature of this head was vastly different intake port location and geometry, compared with the "cathedral" intake port used in LS1, 2 and 6 heads. This different intake port architecture would have far-reaching effects on Small-Block V8s over the next dozen years.
A Katech C5-R 427. Look at all those carbon fiber parts on that engine. Fast as hell and great eye candy. Image: GM Powertrain.
Corvettes dominated LeMans, Sebring and Daytona during the C5 era. Under their hoods was a 600+ horsepower 427. Shown is a C5-R in the esses between the Dunlop Bridge and Tertre Rouge during the 2001 24 Hours of Le Mans. Image: Richard Prince.
John Rydzewski, currently Assistant Chief Engineer for Passenger Car Small-Block V8 Engines, said in a 2008 interview about that head, "A key enabler of this was 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 less bosses in the way of the flow path. The result is a huge improvement in performance."
Six-four development progressed into the Fall of 2002, but there was growing skepticism about displacement. Some were thinking that closer to seven-liters might be necessary. Elsewhere in GMPT, people were doing computer analysis of what it might take to reach the 500-horsepower level and that pointed at 7.0L, too.
Dave Muscaro, who, six months later, would be appointed as Assistant Chief Engineer Passenger Car V8s, told us about that period. "From a 6.4L vs 7.0L perspective, the goal of making 500 hp came sometime before I joined the program. I have a file showing analysis work to probe this power level was done at the end of October 2002. The analysis work was simply to see what airflow, friction, induction and exhaust restrictions, compression ratio, etc, etc, would be needed to create 500 hp. At that time, it was recognized that the engine displacement would likely need to go to 7.0L.
The first time the CAC visited with John Rydzewski, the subject was the LS3 and the cylinder head it used which was derived from the still-born six-four. Image: Author.
Winter of 2002/2003. Six-four development was well into the hardware stage. GM Vice Chairman for Global Product Development, Bob Lutz, along with senior Powertrain executives, then GM Powertrain Group Vice President, Tom Stephens, and then Small-Block Chief Engineer, Sam Winegarden, upset the apple cart by deciding the first number in the C6 Z06's power rating must be a "5". While this decision is a well-known part of LS7 history which added to its mystique, it would be ridiculous to assume that, one Friday after work, Bob, Tom and Sam, got together for beer and burgers then wrote "500-hp" on a bar napkin. More likely is that Mr. Lutz,, Mr. Stephens and Mr. Winegarden reviewed some of the analysis data Muscaro cites, considered where their V8 engine technology was then and where they wanted Corvette to be power-wise in the next five years, then set 500 horses has a goal for their engineers.
Why?
"Competitive Pressure was part of it. The Viper was one of the competitors out there–probably the biggest–and there were others," John Rydzewski, who took over as ACE from Muscaro in May of 2005, told us in a second, 2012 interview.
A decade ago, the most powerful Corvette engine, the LS6, made 405-hp but the Vette's underhood competition–most high-profile of which was the Dodge Viper's monster (but, also, inefficient) 488-cubic inch, 500-hp V10–was putting the Corvette's power rating to shame. There were others, too: Porsche Turbo-444-horses, Mercedes-Benz SL55 AMG-476-hp and Ferrari 575M Maranello-508-hp.
A 500-hp Corvette? Well...duh.
As Corvette Executive Chief Engineer, Tadge Juechter, who, during the C6 Z06 development, was Assistant Chief under David Hill, explained, "The LS7 is the pure-blood, track engine. When we were developing it, we knew it was going to be normally aspirated. For a while, that engine was going to displace 6.4-liters and the first horsepower target was 450. The base engine was 400. We thought: Oh man, more than 10%–that'd be a nice bump. Remember, with the previous Z06, we were, first, at 385, then 405, so that (50 more horsepower) was our mindset as a good performance delta.
Corvette Executive Chief Engineer, Tadge Juechter discusses the LS7 with the Camaro Homepage. Image: Author.
"The horsepower wars were on and, as we developed (the six-four), we saw these new entries coming out with higher horsepower. We had senior leadership–Lutz, Stephens and others–saying, 'The first number's gotta start with a '5'. At the working level, we wanted to get as much as we could. Powertrain didn't know if they could get to 500. There was a lot of pressure from the higher-ups saying, 'We think you can do it. Let's put that stretch target out there and let's see if you can get there.' They just said, 'Well, the original target was 450 and we're going to see what we can do.'"
About the same time, another decree came from then Chief Hill, himself, who mandated the 2006 Z06 accelerate from 0-60 in less than four-seconds. The only way to do that with the car's weight and 3.42 axle ratio was to stay in first gear, so–this 500-hp engine would, also, be a 7000 RPM engine. It's easy to understand Hill's quest–power to keep the Z06 a player in its market segment into the next decade. At this writing, nine years later, Hill's goal was achieved–by a comfortable margin.
By late Spring, 2003, the six-four was deemed incapable of 500-hp or 7000 RPM, so with newly appointed ACE Muscaro at the helm, the Powertrain folks working on the LS7 hit "reset" and began developing a new and even bigger engine. With the displacement now set at 7-liters, what Katech had been doing with its C5-R engines was even more influential on the Small-Block team at GM Powertrain.
"As to when we 'officially' switched to a 7.0L? That would be hard to pinpoint," Dave Muscaro continued. "Before we 'switch' program direction, we do analysis and then test a 'mule engine' to prove our analysis. At the time I came in, we did not have any 7.0L engines, although a couple were ordered from Katech in November 2002. These engines did not yet exist, but the parts to build them were being contemplated and decided upon. So, when I came on the scene, one of the first things I did was sit down with Katech and devise a development plan to build some engines and start proving our ideas on how to make a 500-hp 7.0L. At this time, there may have been one or two 6.4L engines still running, but I was not much interested in trying to make the smaller engine work for a 500hp target. I do not recall any 'official' date when we decided upon a 7.0L displacement. Since we were short on power right out of the chute with a 7.0L, you can bet I didn't go back and try a smaller engine! So by default, a 7.0L was what it would become."
Katech's Kevin Pranger, who was the "engine guy" for the C5-R and the 7-liter part of the C6.R program. Image: Author.
Kevin Pranger, who was Katech's manager for the C5-R engine program, was, also, interviewed for this article. He described Katech's first efforts at a 7-liter race engine and Powertrain's interest. "We started putting liners in LS1 blocks. Then, GM cast us up a couple of special blocks with thicker aluminum so we could use thick wall liners with a larger bore," Pranger told the CAC. "Those castings allowed us to do some testing. From that, we were able to come up a 4 1/8th bore and a four-inch stroke to make seven-liters. That's when GM decided to build an official, 4 1/8th bore 'C5-R Block'. They were able to amortize the tooling for the race program by selling the block in the (GM Performance Parts) catalog.
"They (Small-Block engineers) started coming over here, looking at what we were doing with the cylinder heads and the block," Pranger continued. "They got a lot of ideas from that. The LS7 head looks a lot like the original C5-R, '005' castings. I think a lot of the LS7 was modeled after what we were doing with the C5-R."
Tadge Juechter expanded upon Kevin Pranger's perspective, "You talk about 'technology transfer' from the race program to the street program? LS7 is a perfect example. Some of the rank-and-file Powertrain engineers weren't accustomed to working on an engine like this, so we actually did get help from Katech and others who'd done race engines who helped with the porting design and other things. There were so many different ideas tried and so many blind alleys traveled down. It was an eye-opening experience. Developing that much power with normal aspiration and meeting emissions standards of today is something special. A lot of the lessons learned can be applied to future engines."
Which they were, as we will see later.
"Significant change was needed to increase engine throughput." John Rydzewski stated about the engine's displacement. "Increasing bore and stroke were enablers for the increased performance. Some of the executive leadership desired a displacement such as the iconic, 427 cubic inches. Our analytical and geometric studies supported the 104.775-mm (4.125-in) bore and 101.6-mm (4.0-in) stroke (7.008-liters or 427.484 cubic inches). They were selected for the LS7 program."
Ya think some of John's "executive leadership" had been waxing nostalgic about 427 Vettes? Having dreams of four-inch-plus pistons and two-inch-plus intake valves? Hearing the seductive sound of a high RPM valvetrain motion? Feeling the thump of a big-inch motor pulling hard in the low-mid-range? Listening to the lopey idle of a big cam? Yeah–that's what those car-guy, true-believers were doing. Thank the car gods there were a few of them left.
In 2012, we met with John Rydzewski, again, with the subject this time being the LS7. Image: Author.
The folks who did the six-four head eventually saw the fruits of their labor on the LS3 under the hood of the '08 Corvette and the 2010 Camaro SS. The '09 ZR-1 and the 2012 ZL1 used nearly the same head, but it was made of a more robust aluminum alloy using a slightly different casting process. From an airflow perspective, the only difference was the supercharged head's intake port "swirl wing." Image: GM Powertrain.
And what of the six-four? Well–it was never considered for production–never made it into a car, in fact, but its development was not for naught. Six years later, the 6.4's head appeared on the Camaro SS's LS3 and L99 and, in 2012, after a slight revision in intake port design along with a change in material and foundry process, it, also, became the cylinder head used on the ZL1's, 6.2-liter supercharged LSA, but again–I digress.
Five hundred horsepower from a normally-aspirated V8 while meeting emissions and fuel economy standards was a tall order in late Spring 2003, when full-scale LS7 development began. Muscaro's Small Block Team was soon burning the midnight oil in a ruthless pursuit of power with a 500-horse, 7000-RPM, emissions-legal, no-guzzler, 427 as its objective.
Actually, perhaps as many kilowatt hours were burned as "midnight oil". General Motors has significant computer modeling and simulation resources. Computer software tools such as "Finite Element Analysis" (FEA), "Uni-Graphics" and "Computational Fluid Dynamics (CFD) were used during design and development. A different block casting and a new head were in the program even before the computers got warmed-up. Other key features of the engine were determined by computer modeling–a forged steel crankshaft, pressed in, rather than cast-in-place, liners and titanium connecting rods were, also, deemed necessary through modeling.
Back in '12, we also met with Sam Winegarden, the top engine guy at General Motors. He told us the LS7 has always been one of his favorite projects. He also gave us some inside views of what it was like when he was the Small Block Chief and LS7 was under development. Sam's story about computer modeling of combustion was a revealing insight to how quickly computers have compressed product development time. Image: Author.
The LS7 was developed on Sam Winegarden's watch as Small-Block Chief Engineer, He tells a great story about computer modeling. "I was still Small-Block Chief, the first time these guys could model combustion. This would have been back in about '03 or '04. Dr. Gary Mendruziac (formerly with GM Advanced Research) started us down this journey and I always remember this. It took him one week to do the model for the induction stroke. Second week, he did the compression stroke. Third week he burned it. The fourth week was the exhaust stroke–a month of computer time to model one cycle. "Now, I can do that in a matter of a few hours. Just to give you an idea for how much faster the computers have gotten in that length of time. Eight years and we've gone two orders of magnitude faster."
GM spent a couple of months on LS7 computer work before the first LS7s were assembled by Katech in the Summer of 2003. Shortly after that, more early development engines were done by Powertrain's experimental engine assemblers in Pontiac. Starting on 24 February 2004, development engines were built at the Performance Build Center.
Special Block and Crank
GM's production, aluminum V8 bare blocks, or "cylinder cases" are cast by Nemak, a world-class foundry in Monterrey, Mexico, which supplies engine manufacturers world-wide. The LS7 case shares qualities Gen 3/4 engines have had since their 1997 debut: deep-skirted, 319-T5 aluminum block, long head bolts threading deep into its main bearing webs, six-bolt main bearing caps, a center thrust bearing and gray iron liners which are centrifugally-cast for increased density to enhance strength and allow thinner cylinder walls. All this makes a lightweight, rigid, block structure offering good durability and reduced friction–all important basics for a specialized engine like the LS7.
The structure of the LS7 basic engine is a specific aluminum cylinder case.
Image: GM Powertrain.
While the case is a Gen 4, it's a little different from its6.2-liter siblings used in other Camaros. It has pressed-in, rather than cast-in-place liners and its water jackets had to be altered to accommodate them. The LS7's bore, 104.775-mm, 3.18-mm larger than that of the existing LS2, was greater than cast-in place liners would tolerate and still have adequate cylinder wall thickness, but it works if partially-siamesed, pressed-in liners are used. The liners, also, extend farther into the crankcase than do the cast in-place units. Because of the the LS7's, long stroke, the extra length is necessary as a guide and support for the thrust side of the piston skirt.
John Rydzewski told us that, after casting, LS7 blocks are shipped to a Linamar Corporation facility in Guelph, Ontario, Canada for rough machining, installation of the pressed-in liners, and finish machining operations. One of those operations, machining "hone over-travel clearance", became a major issue during the engine's late development stage. "When the block is honed, the bottom of the honing tool needs clearance so it doesn't contact the block below the bore," John Rydzewski stated. "Before the honing operation, the block is machined in that area to provide clearance. The resulting surface geometry has a big impact on the block structure. Hone over-travel clearance used to be machined (LS1, -2, -6 and early LS7 development cases) with a 3-mm radius. To get more strength in that area, we eventually changed to a more gentle, 8-mm radius. That was a big durability enabler at the LS7's power level."
The pressed-in liners are siamesed for about a two inch section where two liners would interfere. There's no decrease in wall strength because the flat surfaces of the two liners support each other. Image: Mark Kelly/GM Powertrain.
As the pistons move up and down in their cylinders, they force air in and out of the spaces (or “bays”) beneath them. At high RPM, these flow reversals are rapid, violent and really whip up the oil as well as creating power loss. One way to mitigate this problem is to vent each bay to its neighboring bays. Like other Gen 3 and 4 blocks, production LS7 blocks have openings or "windows" their main bearing webs between bays for this “bay-to-bay breathing". Rydzewski went on to say, "Hone over travel machining, affects the size of the resulting windows in those bulkheads which are very significant to bay-to-bay breathing and horsepower."
In its ruthless pursuit of power, GM didn't just haphazardly put holes in the main webs. In fact, early development LS7 cases did not have windows at all because, initially, GM didn't know how to produce a block with both bay-to-bay breathing windows and reliability at 500-horsepower. Extensive finite element analysis along with thrashing engines to death–in some cases, literally–on the dyno and in prototype Vettes, eventually resulted in the LS7 block having both the necessary bay-to-bay breathing windows and more overall strength than any of its predecessors.
The backside of one of the bay-to-bay breathing windows in an LS7 case. Image: GM Powertrain.
Besides 8-mm hone over travel radii, other changes were made to increase the block's strength for use at the 500-hp level. First, the material used in the main bearing caps was upgraded from forged powdered metal to 1141 steel machined from forged billets. Secondly, each cap is located with by dowels making a more rigid structure once all six bolts are tightened.
Some of Linamar's block machining processes are unique to the LS7, but the final two are noteworthy in that they came directly from racing. While they are standard procedure at places like Katech, they are rare for a production engine. First, all LS7 cases are align-bored with deck plates installed and the head bolts tightened to specification. Second, all LS7 blocks have their liners honed with the same deck plates installed and head bolts tight.
Once Linamar finishes LS7 blocks, they are cleaned and shipped to the Performance Build Center for assembly. We visited the "PBC". in the Winter of 2012 to assemble an LS7 (see:
http://www.corvetteactioncenter.com/...l#.UO29RI51-dU) and while there, we learned there is no pre-assembly parts cleaning at the PBC. When Linamar cleans a block, they are spotless. Other suppliers are, also, required to furnish parts which are clean and ready for assembly. We asked Rob Nichols, the facility's Engineering Supervisor, how they ensure that. "We visually check all parts and if they are not to our liking, we send them back," Nichols told the CAC. "Periodically, we test-wash blocks and crankshafts. Any contaminants fall into a filter we place at the bottom of a wash basin," Nichols told the CAC. "The weight of these filters is pre-measured. We take the filters and sediment and bake them in an oven to dry out the filter and debris. Then, we reweigh the combination. The difference between the base weight and the weight of the filter with debris gives us the amount of sediment washed off of the parts. We have tolerances for the amount allowed. If it falls out of spec, we alert the supplier and (do further testing to) make sure all incoming product is conforming."
LS7 main bearings being installed at the PBC. Mark Kelly/GM Powertrain.
The LS7 was the first production engine to use "increased-eccentricity" main and connecting rod bearings. The term refers to the thickness of the bearing. Eccentric bearings get slightly more thin from the center to the edge where the split line relief starts. The difference in this thickness is the "eccentricity". Mark Damico, Design System Engineer–Small-Block Base Engine, who has worked on the Gen 3/4/5 engine program since 1993, told us that, prior to the LS7, bearings were either the same thickness from the center to edge or they had a very slight eccentricity. LS7 bearings have much more eccentricity, .0006-in for the number 1, 2, 4 and 5 mains and a whopping .0011-in for the rods. This higher level of eccentricity improved durability because bearings of this design flow more oil and are more tolerant of bearing bore distortion which increases with cylinder pressure. Use of high-eccentricity bearings eventually expanded to other Corvette engines, the LS9 in 2009 and LS3 dry-sump in 2010 along with the Camaro's LSA in 2012.
If there's a downside of high-eccentricity bearings it's that clearance checking in the field is a little more complicated in that care must be taken to always check the clearance at about 90° to the bearing part line. Also, parts choices when bearings are replaced can be critical. If aftermarket bearings are chosen they must have a level of eccentricity that is similar to that of OE bearings because–if the bearings have less eccentricity–the engine will have either insufficient oil flow in bearings or–if the bearings have more eccentricity–insufficient oil pressure.
An LS7 rod bearing with its obvious red, polymer coating. In a short period after the first engine start, some of the red wears away leaving the anti-friction polymer coating to fill the microscopic voids in the surface of the aluminum. Image: GM Powertrain.
Until the 2012 model year, bearings of traditional, "tri-metal" (steel backing, bronze second layer and a top layer of lead) construction were used in the LS7's #1, 2, 4 and 5 main bearing positions and in the connecting rods. European Union legislation enacted in 2011 prohibits the import of products containing lead, so the main and con rod bearing designs were changed. Lead was replaced with a synthetic polymer making a "bi-metal-with-polymer" design. The center (#3) main bearing remains aluminum on a steel backing. According to Mark Damico, because of the firing order used on all Gen 3, 4 and 5 V8s, the second and fourth main bearings are subjected to the highest loads. After a long period in service, if an LS7's bearings are going to wear, it'll be the #2 and #4 mains which show it, first. The two end bearings may see a lesser level of wear due to (#1) the accessory drive or (#5) the flywheel. The center main experiences the least vertical load and while it is an increased-eccentricity design, it's never required a lead overlay nor polymer coating.
An early style, 4140 forged steel, LS7 crankshaft. Image: GM Powertrain.
Rolled fillets at the edges of each each bearing journal improve the strength of the crankshaft. All but the front main journals are hollow to both reduce mass and facilitate bay-to-bay breathing. Tungsten, a heavy metal, is used to balance the end two counterweights. Image: GM Powertrain.
An LS7 engine part which I think is so pretty is the crankshaft. With its appealing brownish-coppery color and intricate finish machining–darn it–it's just too cool-looking to be in an engine. The eye candy that they are, LS7 cranks are pretty trick parts for a production application being micro-alloy steel forgings manufactured by specialty supplier, SMI Crankshaft in Fostoria, Ohio. The cranks have some journals which are hollow for less mass and, in the case of main bearing journals, improved bay-to-bay breathing. All the journals have rolled fillets for increased durability and, like race engines, the front and rear counterweights are balanced with "heavy metal" slugs made of tungsten. Early LS7 cranks were 4140 steel. Later LS7 cranks, including all the Camaro units are 44MNSIVS steel. "The reason we switched," John Rydzewski told us, "was it eliminated one of the processes in fabricating it. With 4140, you have to quench and temper the crankshaft before final machining. With this new material, you don't have to quench and temper because (the steel) has a different grain structure. The end result is the same properties but (using the new material) eliminates a step reducing the cost of manufacturing."
Under the watchful eye of PBC Assembler, Mike Priest (left), the author installs a late-style LS7, 44MNSIVS forged steel crankshaft.
Image: Mark Kelly/GM Powertrain.
Featherweight Engine Artwork
Part of the LS7's mystique is its use of titanium. Its connecting rods and intake valves are a rare application of that lightweight material in a production engine.
To get the LS7 to reliably turn 7100 RPM, lightweight titanium rods and intake valves were required. Image: Author.
Titanium is a silver-gray metal. The ninth most abundant metal, it's often found in mineral deposits and small amounts are in most living things. Number 22, on the periodic table, engineers often refer to it by its chemical abbreviation "Ti" (pronounced "tie"). Titanium's density is somewhere between that of aluminum and stainless steel. As strong as some steels, but 45% lighter, It has the highest strength-to-mass ratio of any metal. Its other noted property is excellent resistance to corrosion. It is slow to react with water and air because it forms its own, oxide coating which protects it from further reaction. Ti is fairly hard, non-magnetic and does not conduct heat or electricity very well. Interestingly, besides aerospace, military and industrial applications–and LS7 engine parts–titanium is a popular metal for jewelry. Before I got married, my then-fiancée asked me what kind of wedding ring I wanted. "Titanium, because of its strength-to-mass ratio my dear."
Making Ti engine parts isn't easy. While the metal is abundant, it rarely occurs in pure form. Typically, it's produced using the "Kroll Process", a complicated and quite costly pyrometallurgical procedure. In a series of high-temperature chemical reactions, raw titanium "sponge" is extracted from rutile, a common mineral.. Next, Ti sponge is melted into ingots. Since titanium ignites before its melting point is reached, this is done in a vacuum or an inert atmosphere–other than nitrogen, of course, because Ti is one of the few elements which burns in pure nitrogen. The Vacuum Arc Remelt (VAR) process produces titanium ingots which are then rolled into flat or bar stock then forged into LS7 rods and intake valves. Machining titanium can be difficult, because it galls or softens if improper tooling or inadequate cooling is used, i.e.: if you screw-up the machining process, a lot of expensive raw material ends up scrap. How expensive? At this writing, titanium ingots run about $10.30 a pound. For comparison, aluminum was about 93 cents a pound and benchmark, cold-rolled steel was about 37 cents a pound.
The LS7's forged titanium con rod is a work-of-art in many ways. Visually, it's so pretty that, if they weren't so expensive, people would buy them as intriguing Christmas tree ornaments, attention-getting paper weights, unusual props for jugglers or for "industrial-chic" themed interior decorating. Ok, seriously–the Ti connecting rod is pretty because of the silvery-gold-colored, chrome-nitride (CrN) coating typical of titanium engine parts. It's, also, a work of "engine-development-art" as it took a lot of computer analysis and engine testing to get it to where it could be reliable and durable to the standards GM has for all production engines.
The LS3 rod on the scale weighs in at 22.74-oz. The LS7 Ti rod in the foreground weighs 16.38-oz., 28% less. Image: Author.
Why a Ti rod? Not for the reasons most might think. Indeed, substituting forged titanium for forged steel significantly reduces mass allowing the rotating assembly to accelerate quicker improving the engine's response and reducing parasitic losses as the engine speed accelerates, however, titanium LS7 rods are more a durability measure than a performance enhancement.
On the power stroke, when the piston and rod assembly reach the bottom of their travel, inertia combined with what's left of combustion pressure apply a great deal of load on the oil film between the upper bearing shell and the crankshaft journal. During LS7 computer modeling, the Small-Block team discovered that with the, Group III, 5W30 synthetic engine oil used in Corvette engines, connecting rod bearing oil film strength would be unacceptable when the engine was under the heaviest load and at high RPM. Further, they decided a titanium rod would provide the mass reduction necessary to decrease those inertia loads such they would not exceed the film strength of the oil.
"During development of the 6.4-liter, we didn't use a ti con rod," John Rydzewski said. "It was an investment-cast (steel) con rod. It had a lot of mass lightener pockets–less material (than a forged LS6 rod) to keep the mass down. However, with the seven-liter, the longer stroke and higher engine RPM was a concern for proper oil film thickness.
During one of the CHpg's LS7 interview sessions, Asst. Chief Engineer, Rydzewski discussed the LS7's titanium rod. GM Powertrain's Communications Manager, Tom Read looks on. Image: Author.
"Our analysis capability is really good for oil film thickness. This analysis comprehends engine speeds, loads, temperature, mass/inertia and geometry. At high speed, you have a lot of inertia, a lot of reciprocating mass which will reduce oil film thickness. We had to make a big move to increase the film thickness robustness. That (a titanium rod) was the most straight forward way to do it."
That begs the question: rather than an expensive set of Ti rods, why not just a better engine oil? You can buy a lot of premium, ester-based, 10W30 synthetic oil, which has better film-strength properties, for the cost of those rods.
Well...it's just not that simple. To use forged steel rods and a higher film-strength oil, General Motors would, first, have to admit that fabled Mobil 1 5W30 and its "Dexos 1" successor, were inadequate for use in the LS7. That was so not-gonna-happen. Plus–while it is true that there are engine oil products with better film strength properties than the factory-fill 5W30 used in LS7s; when we asked John Rydzewski about that, he commented, "A higher weight oil can improve film thickness, but that, alone, would not have met the design requirements." So, the LS7 has those bitchen ti rods, with their durability advantages and the better throttle response they provide, to add to its mystique.
Rydzewski continued, "Titanium rods are good for reducing reciprocating mass but their downsides are: they are expensive, (Note: we couldn't get cost numbers from GM but, according to Stan Lorence, Parts Manager at Tom Henry Chevrolet in Bakerstown PA, a replacement LS7 titanium rod is nearly four times the price of a steel, LS3 rod). They take a lot of machining steps. They come from Mahle in Germany, so there is a long lead-time. The process–forging, a lot of machining and application of the (chromium nitride) coating–is complicated. There are few suppliers out there which can do titanium rods for production applications.
"We've had pretty good luck with them. We've never broken a rod because of the strength. An unusual property of a titanium rod (compared to a steel rod) is its different modulus of elasticity. They bend a little bit differently and that concerned us at first. Because of the different modulus of Ti, the stiffness requirements had to be comprehended in the design. Many sections of the Ti rod were larger than required for a con rod made of conventional (forged steel).
"Also, we had issues with 'Ti dust wear' during our first round of builds. And then we started seeing some signs later on, once we got into parts that came off manufacturing equipment. The two rods (on the same crankshaft journal) rub against each other. Titanium on titanium does not wear well. If you have sharp corners, particles can break off. They get between the rods and start wearing away the coating and get you into trouble."
The arrow points to the groove or divot which was added to LS7 rods to combat Ti dust. Image: Author.
Ti dust forced implementation of special manufacturing procedures at Mahle. At the part line between the rod and cap, there can be slight misalignment resulting in a sharp edge which can abrade the adjacent rod. The ti dust problem was traced to that area. For engines built for the second phase of development, a small groove was added on the sides of the rod's big end right at the parting line which eliminated the possibility of any sharp edges. Besides Ti dust control, during the LS7 development, other procedures were introduced to avoid impact damage to the rod which causes stress risers and damages the coating.
Cutting-Edge Piston
In a departure from what most people, including some veteran mechanical engineers, would expect, the LS7 engine does not use a forged aluminum piston. It uses a cast, eutectic aluminum piston, but that's greatly simplifying the issue as there's quite a story to the LS7 piston. "They started out with forged on the six-four." John Rydzewski told the CHpg. "When they picked a (piston) supplier for the seven-liter, it was Mahle which came back and said, 'We can do this in a cast piston. We've got the knowledge and it will work.' The decision was to proceed with a cast piston. It met all the requirements–met the specifications and it was less expensive."
In February of 2012, we visited Katech to learn more about its role in helping GM bring the LS7 to market and cast piston was an issue we covered. "One of the big challenges with a cast piston was durability at 7000 RPM," Katech's CEO, Fritz Kayl, told us. "We did stuff later in the program on that. We met the power targets pretty easy but the durability side was more of a problem. The big challenges were piston speed and how to reduce parasitic losses.
"With a four-inch stroke, you have tremendous piston speed. I'll give credit to GM–they set that (cast piston) as a challenge and they were not going to give-up on it. Certainly we didn't have that technology here. Everything we do in racing is forged pistons, but with the LS7, forged pistons were off the table.
Katech's Fritz Kahl explained piston speed to us in an interview at his Clinton Township, MI facility. While the LS7s piston speed is only 200 feet/min. higher than that of the C5-R race engine, inertia loading on the pin and pin bosses increases with the square of the speed and the LS7 uses cast pistons while the C5-R engine used forged. Image: Author.
"At that time, piston speed for racing (C5-R forged piston) was about 4500 feet-per-minute but 7100-RPM for a Corvette LS7 is 4700 feet-per-minute. (LS2 and LS3 cast piston speeds max'ed at 4000-fpm.) And of course, bearing loads and everything else goes up with (the square of) piston speed. That's why the concern. They had some problems with pistons in the early going but they got it solved. As it turned-out, they (GM and Mahle) were right. Those pistons are durable.
So, how did Mahle pull off an advancement some thought impossible? By combining a special aluminum alloy with a new casting method, more robust heat treating and new developments in piston structure.
The LS7 piston is cast from a eutectic aluminum/silicon alloy having small amounts of copper and nickel. This alloy, "Mahle 142," was first used for pistons in the LS6 engine of 2001. "M142" offers increased strength and less expansion at high temperature providing better control of piston-to-bore clearance, both at the skirt and the ring lands. That improved dimensional stability reduces piston noise, improves oil control and enhances durability.
In an interview, Aaron Dick, the Application Manager assigned to the LS7 piston development at Mahle, told the CAC, "We did (a cast piston) primarily for weight-reduction. A requirement was very lightweight reciprocating masses. Taking that challenge, we looked at a new, patented casting process we had. We were able to cast the piston lighter than we could make a forging."
Mahle developed the "Ecoform" casting process in the early-'00s as a mass reduction strategy and LS7 was one of its first applications. This casting technology creates recesses, or cavities, in the ring belt which could not exist in a forging. The resulting high-strength, reduced-mass, cast piston was cutting edge technology for high-volume, production engines in the mid-'00s.
This cutaway Mahle Ecoform piston, while not an LS7 unit, is typical of pistons made with that process. It is very light because of cavities the process forms in the underside of the piston which could not exist in a forging. Image: Mahle.
The heat treat specification for the LS7 piston is, also, a departure from the norm and intended to improve strength. "The vast majority of gasoline pistons have a T5 heat treat where the LS7 has a T7 heat treatment," Dick continued. "That increases the strength and the hardness of the piston and that adds strength at the pin bosses–the lower temperature parts of the piston. At high temperatures, the heat treatment is not as critical. In the piston crown, for example, it's not helping as much, but in the lower end of the piston, the T7 heat treat improves the properties of the material. This helps when you have 'inertia loads'–high speed but no load. For example: if you downshifted going into a corner, when the engine revs up, (inertia loads) are trying to rip the piston pin out of the piston."
The LS7 piston has "asymmetric" skirts with the major thrust face being wider than the minor face, a configuration responsible for another slight mass decrease. The skirts are coated with "Grafal", Mahle's proprietary, polymer coating which reduces friction, increases scuffing resistance and allows less piston-to-bore clearance leading to less engine noise.
The underside of an LS7 piston and its wrist pin are both engineered for reduced mass. Image: Author
An LS7 piston pin, or "wrist pin"–arguably one of the most highly stressed parts in a high-performance engine–is made of a gas-nitrided, chromium-molybdenum-vanadium steel meeting the 31CrMoV9 specification. This is a more robust material than normally used in GM V8 pistons. it allowed the wall thickness of the pin to be less and the inside diameter to be tapered to reduce mass but still enabled the pin to meet GM's abusive fatigue life tests. The piston is phosphate-coated, the main purpose of which is to improve the reliability of the pin bores during the break-in period. The pin locks are circlips, but they're made with 1.8-mm rather than 1.6-mm wire to increase the circlip's tension. During development, according to then Small-Block Chief, Sam Winegarden, the LS7 engineers learned that, at high RPM, the loads on the 1.6-mm circlip at top-dead-center and bottom-dead-center can deform it and pop it right out of the pin lock groove. Going to the more robust circlip solved that problem.
More "light-weighting" comes with the LS7 piston's skirt asymmetry. Image: Author.
Areas immediately adjacent to the top ring groove are hard anodized and the surfaces of the piston skirts are coated with Grafal, a polymer-based antifriction material pioneered by Mahle with the 2002 LS6 piston. Image: Author.
Again, looking at the underside of the piston, to increase strength, the top portion of the wrist pin bore bosses, indicated by the shorter arrows, are wider than the bottom portion.
Image: Author.
Additional mass reduction comes in shortening the piston pin, but to do that and preserve the ability of the pin bosses to carry the load, the pin bores were moved closer together and the tops of the pin bores curve inward to further strengthen that area. To clear those parts of the pin bores, the small end of the connecting rod is formed with a pronounced step with the top being more narrow. Another reason for a shorter pin? It provides clearance between the crankshaft reluctor wheel and number eight piston.
An '06-'11 Corvette LS7 piston/rod assembly. The Camaro unit is identical except for a polymer-coated, bi-metal rod bearing. The four valve reliefs are a welcome feature of the piston top for those wanting to go to an aftermarket cam profile.
Image: GM Powertrain.
The piston top has four valve reliefs which, according to Aaron Dick, are not necessary with the stock LS7's valve lift. They exist because, after the design was finalized, GM wanted slightly less compression, so four valve reliefs were added. An unintended, but sometimes welcome consequence, is that these reliefs provide adequate valve-to-piston clearance for some aftermarket camshafts, such as Katech's "Torquer" series of LS7 cams, having more aggressive profiles without having to change pistons. The ring grooves are machined with a slight upward tilt which counteracts the rings' tendency to flex downward under operating pressures and temperatures. The top ring land is hard anodized to prevent microwelding on the flanks of the ring groove.
The top ring is filled with moly as an antifriction measure. The LS7's Napier second ring was developed for the 2002 LS6 and later used on all Small-Blocks. A "Napier ring" has a distinct shape that enhances oil control by scraping oil off the cylinder walls as the piston moves down in the bore. Image: Author.
The LS7 ring package starts with a 1.2-mm, moly-filled, steel top ring. It is "coined" to give it an upward twist which flattens under combustion pressure improving ring seal. The second ring is, also, 1.2-mm, but is made of ductile-iron and has a Napier-face for enhanced oil control. The oil ring is a 2-mm, 3-piece unit consisting of two gas-nitrided rails and an expander.
Most of this cutting-edge piston technology is aimed at reducing mass but, also, increasing durability. Aaron Dick's closing statement says it all about the level of technical sophistication in the piston assembly: "it's a very, highly-engineered piece for a specialized application."
During engine assembly, techniques similar to those used in the engine shops at Katech or Hendrick Motorsports are used to install the pistons, including an awesome ring compressor which the author insists would look excellent in his tool box. Image: Mark Kelly/GM Powertrain.
Dry-Sump Oiling
The performance requirements Dave Hill's Corvette Team gave the folks at Powertrain were demanding: 500-hp, 7000 RPM and engine reliability under levels of acceleration, braking and cornering forces unattained by previous stock Corvettes. Computer modeling quickly demonstrated that, to meet those requirements, the Z06's wet sump oiling days were over. Even the best of GM's wet sumps, the fabled "bat-wing" oil pan of the C5 days, could not be relied upon for consistent oil flow at the LS7's lofty RPM range and at the Z06's gut-wrenching handling limits, so LS7 became the first production GM engine to use a dry sump oiling system.
Mocked up in the photo studio, the 2010-2014-spec., LS7, dry sump components.
Image: GM Powertrain.
"Our biggest surprise was Powertrain's choice of a dry sump." Katech's Fritz Kayl told us. "In the early parts of the program, we were able to show them what performance advantages you can get out of dry sump system, but we never thought they would consider it.
"We bid on doing the dry sump for that engine but we did not get it, so we weren't really involved in the production side too much. The actual production dry sump system running the scavenge pump off the crank, behind the pressure pump, I thought, was pretty unique and it works pretty well. Certainly not an all-out race set-up, but darn good for a production car."
Late LS7 oil pan. Image: GM Powertrain.
Actually, "dry" sump is a misnomer because it's not truly dry, at least in the sense of some of the complicated dry-sump systems on C5-Rs or a NASCAR Sprint Cup car. The LS7 system is more of a "semi-dry" sump in that there's oil inside the crankcase and the oil pan. What's different is the "sump" part–that is, the engine's entire oil supply–is not stored in the lower part of the oil pan beneath the crankcase, but rather in a remote-mounted tank. The oil pan contains a limited amount of oil, because, when the engine is running, it's constantly drained or "scavenged" by a "scavenge pump".
"GM had never developed one before," John Rydzewski began his discussion of the dry sump. "We benchmarked systems on racing engines and from other manufacturers which have (production) dry sumps like Porsche and Ferrari. We saw how complicated they are. You can do a very complex, multi-scavenge with each (crankcase) bay scavenged individually by a pump having five stages, like on a race engine. That's the extreme and not what we wanted for this car. We wanted something to give us the performance we needed. We wanted it more affordable. We wanted to make it as compact as possible."
LS7, two-stage oil pump components. Image: GM Powertrain.
The LS7 development team settled on a two-stage design. Gen 3/4 engines already had crankshaft-driven, gerotor oil pumps, so it made sense to add a second gerotor scavenge pump. Both are inside a two-cavity housing located at the normal oil pump position on the front of the block.
Oil is sucked out of the bottom of the pan, into the scavenge pump, through a passage in the bottom of the pan, then through hoses and into the dry sump tank located in the right rear corner of the engine compartment. Oil enters the bottom of the tank and flows through a tube to the top of the tank. Flow then reverses through a system of baffles and perforations, down the inside perimeter of the tank. That spiraling, downward flow separates the air and crankcase gases out of the oil.
The Camaro LS7 oil tank. Image: GM Powertrain.
The lower part of the tank is the engine's oil reservoir. The air and gases rise to the top, are ingested by the Positive Crankcase Ventilation (PCV) system and consumed by the engine. At the bottom of this tank is conditioned oil–"conditioned" meaning the vast majority of air and gases are gone and it's a little bit cooler because it's been in the tank for a while. On top of that, as the engine is subjected to accelerating, braking and cornering forces, the pick-up tube is always submerged. It doesn't suck air and that's the key to the reliable, consistent oil supply an LS7 needs.
An LS7 oil heat exchanger. Image: Author.
Like most road racing engines, the Z/28's dry-sump system includes an engine oil cooler. It is an oil-to-coolant heat exchanger originally developed for the C6 Corvette ZR1 and is bolted to the oil pan on the driver side of the engine.