2009 Corvette ZR1: Ruthless Pursuit of Power: Supercharged Edition - Page 4 of 7

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© 2008 by Hib Halverson
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A Little History

Now that we covered the supercharger, before we get to the rest of the engine, set the Wayback Machine for about Christmas, 2004 about the time GM Powertrain was doing early research which would drive some of the LS9's major design features.

That preliminary study resulted in several major conclusions:

1.  Early computer simulations demonstrated that a normally-aspirated engine would have to be larger than 8.0-liters to meet a 600hp goal, but the Small-Block architecture would not support such a large displacement.
2.  In these early sims a V10 was, also, briefly considered, but quickly discarded because it wouldn't fit the C6 platform.
3.  A Roots type supercharger would provide the required power increase and offer instantaneous boost.
4.  The LS7 cylinder block would not work as a basis because its cylinder walls lacked adequate thickness for good durability in a supercharged application,
5.  The 6.2-liter block, then under development for use in high-performance SUVs and the base Corvette, with a few additional upgrades, seemed a good candidate for use in this engine because of cylinder walls about .011" thicker.
6.  The "first-design" LS7 head, which didn't make production, but was used later on the LS3 could be revised somewhat and used on the blown engine.
7.  The goal became 100 horsepower per liter of displacement.

GM Powertrain would have to meet all seven of those goals and then, it would have to get the result sized to fit into a C6 Vette without resorting to any kind of obvious "power bulge" the hood. "Probably the packaging issues were the biggest challenge early-on," Ron Meegan told us. "Just because we were so compressed heightwise, and lengthwise, not so much widthwise and because we knew the LS7 and the LS3 were in there. That was our biggest issue at the beginning."

Corvette's exterior designer, Kirk Bennion, tells a great story about early sketches of the Blue Devil, which had a pronounced bulge in the hood to clear something presumably the size Eaton's M156 fifth-gen blower prototype, being shown to the car's Vehicle Line Executive at the time, David Hill. Anyone who worked for Hill knew of the "stare" and the VLE's sometimes acrid responses to proposed changes to the car which he did not favor. It is said that Hill's displeasure with the idea of a pronounced power bulge was considerable and resulted in a protracted version of the "stare". VLE Hill's demand for a compact supercharged engine made packaging the most taxing aspect of the program.

The formal program began with a presentation the Small-Block Engineering Team made to GM Powertrain management on January 12, 2005. Two weeks later, GMPT approved the project. On Feb. 18th, Meegan's team first ran the POC six-liter on on an engine dyno.

On May 11 that year, GM's North American Strategy Board, the corporate entity in existence back then which made the major investment decisions on GM's North American programs, gave its blessing and, with that, Ron Meegan and his bunch had approval to begin full-scale, product development of the most powerful, production V8 engine ever manufactured by an American car company.

On 3/3/06, the first "beta" engine ran on a dyno. In the GM lexicon, "beta" means the engine is of design intent but assembled from prototype parts. About a month later the LS9 was approved for production as a 2009 model year (MY09) program. On June 22, the first beta LS9 hit the road at the GM Milford Proving Ground in a "Blue Devil" prototype.

January 2007 had gamma engines running on dynos. "Gammas" are design-intent products built, where possible, with production parts and processes. The first, third-generation ZR1 prototype with a gamma-build engine was assembled in a GM prototype shop in Detroit on 2/22/07 and the first production-intent, pilot ZR1 was built using a gamma motor at Bowling Green Assembly the following May.

The first "pilot" engine, one built to production intent, was assembled at GM Powertrain's "Performance Build Center" in Wixom, MI on Feb. 18th this year. The first saleable ZR1 was built in B.G. during the third week of July, this year.

The Block and Heads: Chips off the "Old" Block and Heads

The aluminum block, or "cylinder case", used in the LS9 is a relative of the unit used in the '08 Vette's LS3 and in the 6.2-liter, L92 GM puts in Cadillac Escalades and GMC Yukons, but it has some key differences.

First, there is a further strengthening of the main bearing webs by once again redesigning their windows. These windows allow the bay-to-bay breathing and oil windage control which helps lessen parasitic power loss and reduce crankcase oil windage.

GM Powertrain did a great deal of finite element analysis (FEA) work in search of a reliability/durability margin at the projected 620-hp similar to what the LS3 has with 430-hp. This research indicated that the windows in both the LS9 case's number-two and -four webs could be further strengthened by reshaping them in a manner that altered the stress concentration in each web. This reshaping, also, resulted in a slight increase in their areas. "Those windows are larger and have a non-symmetrical shape," Ron Meegan told the CAC. "When we made them larger, we were able to move the edge of the opening to a thicker portion of the bulkhead and that is where the strength improvement comes from. We were able to get to this sweet spot using finite element analysis. We incrementally increased the size of the window until we reached the maximum safety factor. If we go larger than this, the safety factor begins to decrease because the size of the hole overrides improvement from the increasing thickness of the bulkhead."

The window in #3, which, previously, was larger than those in the two and four webs, because the center web is the least stressed, was slightly reduced in area to match the profile and area of the other two. Testing proved that slight area decrease did not affect bay-to-bay breathing or crankcase windage.

Click image for larger view As the pistons move, the volume of the crankcase bay below each piston changes rapidly. The windows allow each bay to "breathe" by allowing the piston to push air into or pull air in from an adjacent bay. This bay-to-bay breathing greatly reduces the effects of "windage" on the oil below the crankcase in the oil pan. Less windage means more consistent oil pressure at high rpm and less oil vapor in the PCV system. Image:  GM Powertrain

Click image for larger view The main caps in the LS9 are forged steel and are located by alignment dowels driven into the top portion of the inside main cap bolt holes. Image:  GM Powertrain.

The net result of this latest round of block window alterations was another, 18% increase in strength of the webs and a 36% increase, total, at the LS9's power level., beyond the first Gen 4 block, the LS2. This change is not specific to the LS9 and will be implemented for all V8 aluminum blocks starting in MY09.

Second, the main bearing caps are forged steel, like those those in the LS7, rather than sintered, powdered steel units in other Gen 3/4 engines, and they are aligned with dowel pins, another LS7/LS9 exclusive.

Click image for larger view A supercharged engine transfers a lot of heat to the pistons, so GM added oil squirters to cool the bottoms of the pistons. Image:  GM Powertrain	Click image for larger view Two of these piston squirters are installed into the block in each crankcase bay. The bolt is hollow and screws into the main oil galley. Oil flows up the bolt shank and out the nozzle. The tab, at left, locates the nozzle properly so the oil spray is aimed at the piston bottom. Image:  GM Powertrain.

3) The crankcase is fitted with nozzles which aim an oil spray on the bottom of each piston for enhanced piston cooling and there is an interesting side benefit of them. "The oil squirters," Ron Meegan told the CAC, "are targeted to spray on the un-derside of the piston at TDC. As the piston moves up and down the bore, some of the oil gets deposited on the bore and the (acoustic insulating) effect of additional oil on the bore provides a noise benefit." These squirters screw into small passages drilled into the main bearing oil galley, 4) the block is threaded for larger, 12-mm head bolts and 5) it is bored and honed with deck plates bolted in place. Other aspects of the LS9 block carry over from the LS3, about which additional details can be found in the CAC's LS3 article.

Like all Gen 4 aluminum blocks, the units for the supercharged (SC) Small-Blocks are cast by Nemak in Monterey, Mexico, however, the LS9 case is finish-machined by Albert Weber GmbH. Initially the work was done in the company's plant in Germany, but that task is soon to be moved to its manufacturing facility in Charleston, South Carolina.