|Viper’s 8.4-liter engine was designed for improved emission performance to meet the new regs—but there’s also greater performance overall, with an increase to 600 hp.|
When it came time for Chrysler to develop the V10 engine to power the 2008 Dodge Viper SRT-10, the automaker turned to McLaren Performance Technologies (Livonia, MI; http://www.mclarenperformance.com) and Ricardo Inc. (Van Buren Township, MI; http://www.ricardo.com) to assist in the engineering and development process. Pete Gladysz, senior manager, powertrain-SRT, explained that the relationship between the companies was close. Speaking of the McLaren and Ricardo engineers, he said, “They worked internally next to Chrysler engineers to do the design and development and dynamometer work for the program because we wanted the experts to be our partners.” The collaboration produced an engine that is larger, more powerful and, more importantly, cleaner—the engine exceeds Federal tier 2, bin 5 as well as CARB LEV2 emission mandates—than its predecessor. Power was vital. “We realized that if we had taken a step backwards in horsepower nobody would have bought the car,” Gladysz said.
|The two-piece air intake module handles larger volumes while keeping the engine running smoothly during all operating conditions.|
Processing for Power
The initial internal target was to boost horsepower by 50 from the previous Viper’s 500-hp rating. They easily exceeded the goal by pumping 600 horses and 560 lb.-ft. of torque out of this 10-cylinder. How’d they do it? First, they increased the bore by 1 mm, which resulted in a boost in displacement to 8.4-liters from the previous 8.3. The next crucial step was to assure the proper amount of air and fuel entered the combustion chamber, which required a new engine controller, dubbed “VENOM.” Developed by Continental AG (www.conti-online.com), the controller is capable of monitoring the crankshaft and cylinder position up to six times during each firing, improving airflow and fuel control dramatically from the previous motor’s single data calculation. “Our processor power went up about 10 times thanks to the new processor package. We will know where the crankshaft is at any point in time during the engine’s operation which means all of our calculations when it comes to air/fuel mixture will be much more accurate,” Gladysz said. The additional computing power was needed also to help manage the variable valve technology (VVT), which itself was being introduced to the Viper to improve the behavior of the engine at idle and varying speeds. A specially-designed concentric VVT camshaft was developed by Mechadyne International (Oxfordshire, UK; http://www.mechadyne-int.com) and manufactured by Mahle (http://www.mahle.com) complete with two concentric shafts in a single assembly constructed from a solid inner camshaft and outer cam tube. The outer tube is where the exhaust lobes are located, while the inner shaft houses the intake lobes, allowing the valves to adjust based on the requirements of the engine at varying speeds. “The way the old Viper engine was designed it had a lot of internal EGR [exhaust gas recirculation] from valve overlap and we discovered the only way to make the big horsepower number and have a smooth idle in the same package was to apply a device that would limit the overlap and allow the engine to run overall very smoothly,” said Gladysz, who predicts the Mechadyne concentric camshaft tech-nology will be adopted by other OEMs interested in maintaining the longevity of pushrod engines.
According to Gladysz, the V10 is the first engine to feature VVT on a high-performance cam-in-block engine, requiring reengineering of the engine’s air intake and exhaust modules to better manage power, fuel economy and emission requirements. The air intake manifold combines a cast aluminum lower plenum with smooth runners for better air flow, bolted to a die-cast aluminum upper plenum. A revised air-cleaner box with a low-restriction filter sends air through a dual electronic throttle control—with throttle blades taken from the 4.7-liter V8 debuting in the 2008 Dodge Dakota pickup—into the intake module, which better manages the air flow. “With VVT technology you have to really be mindful of the airflow and the only way to do that is to manage it electronically. This is the first time in the corporation’s history that we have developed an air low metered engine. We haven’t taken this step in the past because there has been a cost associated with it, but we have to do it in order to manage the cam more effectively,” Gladysz said. The intake also has a higher capacity over the previous engine, capable of pumping up to 12 liters of air into the engine.
Valvetrain Goes on a Diet
Chrysler’s clean sheet approach to developing the 8.4-liter V10 resulted in a number of other revisions, including new springs, bigger valves, and new chambers on the cylinder heads designed to reduce the amount of fuel that used to sit on the walls of the heads. “We tried to maximize every piece of the equation,” Gladysz said. The configuration of the valvetrain was redesigned to reduce weight while improving efficiency at higher rpms through the use of smaller diameter, lighter hydraulic lifters; and fully machined hollow stem intake valves and revised springs designed to work more effectively within the cam profile. The cylinder block is constructed from A356 T6 aluminum with pressed-in-place iron liners, while the piston and rod assemblies are shared with the 6.1-liter V8 HEMI engine used in several SRT-8 performance vehicles. “One of the other things that was critical was to provide the necessary oil passages to support cam operation effectively,” said Gladysz, while pointing out the engine’s larger oil pump and revised oil filter—designed to reduce restriction and provide higher differential pressure capability. “The trickery of this whole engine was doing a cam and then controlling the cam effectively with the controller. We have about ten times the code in the controller and managing all that code and the cam are the biggest two technological breakthroughs we tackled,” said Gladysz.
Powertrains Crucial for Chrysler’s Survival
Although DaimlerChrysler CEO Dieter Zetsche’s comment about all options being on the table so far as Chrysler Group’s future goes, Chrysler is not stopping its investments in new developments. For example, plans call for investing $3-billion in new powertrains—including a family of V6 engines and dual-clutch transmissions—in the coming years. Nearly $2 billion has been allocated for the new “Phoenix” V6 engine family which will be built on a single architecture (rumored to come in four sizes: 3.0, 3.3, 3.6 and 4.0 liters), as opposed to the four architectures currently used. What’s more, it will be manufactured at new facilities in Wisconsin, Michigan and Germany and installed in both Chrysler and Mercedes-Benz brand vehicles. While the automaker is mum on the exact timing of the launch of the engine, sources indicate it could be used on the next-generation RT minivans, as well as future LX rear-drive passenger cars and numerous SUVs.
On the technology front, Mercedes is likely to get direct-injection for their versions of the engine. Besides the engines, Chrysler is also slated to get a dual-clutch transmission from Getrag loosely based on the Powershift system the supplier developed through a joint venture with Ford. This transmission will be mated to the new Phoenix engine. Also on tap is a new mild hybrid to be developed in conjunction with BMW, which is already working in conjunction with DaimlerChrysler on the two-mode hybrid system slated to hit the market in 2008 Dodge Durango.