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<< 2008 Corvette Tech Center

2009 Corvette Tech Center >>

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

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© 2008 by Hib Halverson
No use without permission, All Rights Reserved

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Fuel System, Ignition, PCV and Exhaust

The LS9 fuel system must provide a wide range of flow rates, from wide-open-throttle (WOT) at 638hp, to part throttle cruising on the highway getting 25 mpg and smoothly idling through the takeout window at Burger King and everything in between. That's a very wide dynamic range, too wide a range for a system using a single fuel pressure to control. ZR1s have a fuel system control module which sets the LS9's fuel pressure at one of three levels, depending on fuel flow: 250 kPa, for operation requiring less than 15 grams per second fuel flow, 500 kPa for operation requiring between 15 and 45 g/s and 600 kPa for high-rpm, wide-open-throttle operation needing more than 45 g/s. The engine's fuel need at peak power is about 58 g/s at 600 kPa.

Obviously, feeding an engine generating 638-hp requires a "big" injector. LS9 uses injectors rated for 6.52 g/sec. (51.7 lbs/hr) at 400kPa and which have about 20% greater flow capacity than the units in an LS7. In addition, they are "bent spray" injectors, the use of which was a packaging choice allowing the injector to be mounted vertically—to minimize flow restriction caused by the injector cavities in the intake manifold—but spray at the back of the intake valve. "The fuel comes out of the injector at an angle." Yoon Lee told us. "Think about a fuel injector for a four-valve engine. The injector (spray) will spread out. (You) have two sprays, one targeted on the back of each intake valve. So the technology was already out there to make the injector spray at an angle, off the centerline of the injector. Think of this as a dual spray injector for a four-valve engine, but you're only using one leg of it. That means the injector has to oriented a certain way. The orientation feature is in the injector clip to the fuel rail. You can only install the clip if the injector is correctly oriented."

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The LS9's fuel rail is unique in that: 1) it has a flexible hose section in it to allow installation on the intake plenum with the injectors seating into the pockets cast into the manifold and 2) it uses a center fed crossover pipe and center fed side logs to reduce fuel pressure variation across the set of injectors and to reduce noise the variations can cause.
Image:  GM Powertrain
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The ignition coils were relocated to lower their positions and increase underhood space.
Image:  Author.

The LS9 ignition system has some new features, too. First, the coils, which carry over from LS3 and LS7, are mounted directly to the valve covers rather than to the mounting bracket common on other Gen 3/4 engines. As this brought the coils closer to the plugs, the spark plug wires on an LS9 are shorter. Finally, a high-tech spark plug, sourced from Denso, is used. It has an iridium tip and a ground electrode with a platinum pad. These iridium-platinum plugs (iridiplats?) are, also, a Denso 20 heat range, colder than the 16s used in other Denso-equipped, GM engines.

Long gone are days when positive crankcase ventilation systems were a PCV valve stuck in the valve cover, a hose from it to the intake manifold and a fresh air source. Today's PCV systems are critical, not only for exhaust emissions and durability, but also for performance. They help control the oil windage, which increases parasitic power loss, and are key to reducing oil ingestion at high rpm which makes the engine more prone to detonation, increases oil consumption and degrades catalytic converter life. The PCV system must address all those concerns. To do all that with an engine having a relatively small crankcase volume and a dry sump oiling system requires a sophisticated design.

The LS9's PCV hardware builds on the LS6, LS2, LS3 and LS7 designs. A discussion of both the LS2 and LS3 systems can be found elsewhere on the CAC. Both the "foul" (normally flows from crankcase to intake) and the "fresh" (normally flows from just downstream of the air filter to crankcase) sides of the system have air-oil separators. On the foul side, that's a given, but, because flow through the fresh side can reverse at WOT and high rpm, in a practice that began with LS2; air-oil separators are used on the fresh side, too. They're located inside each valve cover.

The foul side of the PCV consists of an air-oil separator and PCV valve built into the valley cover and a short hose running from the front of the valley cover to a port in the supercharger case just behind the throttle body.

The flow path through the system during normal operation is: from the intake air duct, via a pipe to the dry sump tank and then from the tank to a tee above the back of the right valve cover. From there, one line runs along the back of the engine to the rear of left valve cover and the other runs up to the front of the right cover. PCV air enters the engine at the valve covers, circulates through the inside of the engine, exits through the valley cover and is sucked into the engine through the port in the blower case. At WOT, flow on the fresh side may reverse with foul air going though the fresh side air-oil separator to the dry sump tank then back to the air intake where it is expelled into the engine.

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Math art showing the layout of the LS9's PCV hardware. Not shown is the oil tank which would be to the top, left of the engine.
Image:  GM Powertrain
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Two views of the LS7/LS9 exhaust manifold. Left has the shielding removed.
Image:  GM Powertrain.
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The LS9 exhaust outlet. This manifold is best described as a "shorty header" and works very well for an OE manifold.
Image:  Author.

The exhaust manifolds used on an LS9 come straight from the LS7. The double-walled, stainless steel "shorty header" used on that engine along with the close-coupled catalytic converters developed for it were a perfect match for the blown motor. In fact, the entire ZR1 exhaust comes right off the Z06.

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It's amazing how engine controllers have changed much in the last few years. They're smaller and can tolerate mounting right near or even on the engine.
Image:  Author
Powertrain Controller

The Engine Control Module (ECM) or "controller" as the guys who develop this stuff say, was new for 2006. Known internally as "E67", this controller has all the extra inputs and outputs needed to run a supercharged engine and is the top of the line member of GMPT's "Strategic Engine Management Complexity Reduction Initiative" Yeah, GM is like the Federal Government when it comes to thinking up names. This initiative is focused upon servicing the needs of a range of GM engines via a portfolio of distinct ECM designs which provide steps of increased functionality.

E67 has enhanced Electronic Throttle Control (ETC) ability and it supports the 58x crankshaft position signals and 4x camshaft position signals which are becoming the standard at GM. It is a thermally-robust design which can survive under-hood mounting 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 E67: its CPU is Motorola's PowerPC, a sort of second-cousin to what runs the MacIntosh Powerbook on which this article is being written. It's a 32-bit RISC processor running at 40Mhz with 64Kb of RAM and 2 Mb of electrically programmable ROM (EPROM or "flash ROM"). Its nonvolatile memory includes partitions for both battery-backed RAM and battery-independent EPROM. The 2 megs of flash ROM contains GM's Engine Control Software as well as the one hundred thousand plus engine calibration elements (the "cal") which give the LS9 its personality.

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On the outside a ZR1 transmission looks generally like C5/C6 trannys have looked since 1997. Inside...it's a different story: beefier parts.
Image:  GM Powertrain
Farther Back

While they're not engine-related, there are other upgrades, specific to the LS9's torque output, which were added to the ZR1's powertrain to increase QRD when the input torque is 604 lbs/ft.

First, there's a new, Sachs, two-plate clutch, the first time this has been tried on a Corvette since 1970. The pressure plate is similar to what's been used in the past on C5 and C6, a diaphragm-type clutch actuated by a concentric, hydraulic slave cylinder. What's different are the two clutch discs. To get enough clutch pressure with one disc to hold 604-lbs/ft torque would have meant unacceptably high clutch pedal effort. A two plate clutch allows less pressure plate spring pressure, thus, its pedal effort decreases below that of a single-plate clutch, but it has increased torque capacity because, with two plates, the system's friction area is increased. While this sounds like having your cake and eating it too, there are no free lunches. The price of a two-plate clutch is an increase in mass due to the addition of the second clutch disc and the floater plate between them.

The ZR1 uses a special, RPO MH3 version of the TREMEC TR6060 six-speed. Its first difference is a big one: a different gear set. All gears except fourth have different ratios making the new King's tranny a "close-ratio" six-speed. There are two reasons for use of a unique gear set with a higher first and smaller ratio spreads: 1) the lower the ratio, the stronger the gears are. With 604 lbs/ft input torque, this is of particular importance in first and second gears and 2) even if first gear could be made strong enough, there's little point in a 2.66 or 2.97 ratio considering 604 lbs/ft of torque will blow the tires away in the first three gears with the new, MH3 gear set, anyway.

MY09 Transmission Ratio Matrix

  MM6
(base and Z06)
MZ6
(Z51)
MH3
(ZR1)
1st
2.66
2.97
2.29
2nd
1.78
2.07
1.61
3rd
1.30
1.43
1.21
4th
1.00
1.00
1.00
5th
0.74
0.84
0.81
6th
0.50
0.57
0.67
Rev
3.42
2.90
3.11

The ZR1 six-speed has other improvements as well. Its input and counter shafts along with fifth and sixth gears are made of more robust, 9310 steel. The structures of the main section of the transmission case and the front and rear adapter plates have been redesigned for increased strength.

The rear axle used in LS9 applications is, also, more robust than other C6 axles. The ring and pinion gears are made of a premium material and shot-peened. The differential housing is made of higher strength steel and the right side cover has been redesigned.

Final Tidbits

A discussion of modern engine design and development wouldn't be complete without a brief look at the role computer simulations and analysis plays in getting any powertrain product of today to market, much less one producing 638-hp.

For example, take "computational fluid dynamics (CFD). It's a computer modeling technique that allows engineers to accurately simulate the flow fluids (air or liquid) through a passage. Think cylinder head airflow studies or modeling coolant flow through the engine's cooling jackets, both of which were applications of CFD during the LS9 development.

Icing on the CFD cake, so to speak, is when you add "rain drop analysis". The addition of the proprietary GM rain drop analysis software code allows modeling airflow systems where liquid droplets are present. It was used to analyze crankcase vapor flow through the LS9's PCV system and it was used to model air flow in the intake ports downstream of the injectors and in the combustion chamber. Obviously, CFD with rain drop analysis requires several "supercomputers" worth of processing power.

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LS9s were thrashed almost endlessly on the engine dyno.
Image:  GM Powertrain
In short, today's computational analysis tools allow the engine wizards at Powertrain to design, develop and test a virtual engine—imagine one of the several "desktop dyno" software programs for personal computer use but multiply the functionality, complexity and accuracy by a factor of a hundred. Analysis shortens the development cycle and reduces its cost. Without computational analysis tools, GM Powertrain probably would never have developed the LS9. Is all this computer analysis stuff to be trusted? You betcha! When all was said and done, during the LS9's SAE power/torque certification testing, it's performance was within 3.5% of what was predicted by sims and analysis.

Durability testing of this engine was pretty brutal. An entire article could be used up describing the punishing tests the engine had to pass, some of which was on engine dynos and the rest was in prototype or pre-production ZR1s. An example is the "1 Tank/WOT" test which begins with a full tank of gas and ends when gauge shows "empty". It's run at or near wide-open-throttle in fifth gear on either a high-banked race track, such as where the NASCAR Sprint Cup Series might race, or on an unrestricted section of the German Autobahn. In the ZR1's case, it was the Autobahn and it was done there because this test on the no-speed-limit section of the famed German highway is, as Tadge Juechter told us, "...a much more abusive test of the car's brakes than cruising around a high-banked oval."

Driving the car in this test, was a highly-skilled, retired race driver and he ran a pre-production ZR1 the same way a "99th percentile" aggressive driver would do with his car. The data from this test validated the car's reliability under extreme duty and, after being corrected to reflect an 86°F ambient temperature (very rare in Germany) it validated the supercharger charge air cooling system's "temperature rise" which was discussed in detail early in this article.

The LS9 was also subjected to a 24-hour validation session during which the only difference between it and a 24-hour road race was the length of the stops for refueling, driver changes, measurements and data acquisitions. That was done using Road Atlanta and Virginia International Raceway. In addition, a number of simulated 24-hour tests were run on GM Powertrain's engine dynamometers. Lastly, the engine was validated for 150,000-mile durability in normal use.

So there you have it. LS9...the most powerful automotive engine ever developed by GM in the most amazing Corvette ever built.

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The most powerful GM engine...ever.
Image:  GM Powertrain
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All these cool parts were made possible by tens of thousands of people at GM and its suppliers. A few of those people gave us special help in producing this article. At GM Powertrain: Communications Assistant Manager, Tom Read; Assistant Chief Engineer, Ron Meegan; Design Responsible Engineers Yoon Lee, Brian Geiser, Lou Oniga and James Cremonesi. On the Corvette Team: Chief Engineer, Tadge Juechter. At Eaton Corporation: Manager Global Communications-Automotive, Jim Parks, Supercharger Advanced Sales Manager, Grant Terry, and Development Manager, Mike Sitar.
Image:  GM Powertrain.

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