Development of the Caliber SRT-4’s turbocharged 2.4-liter 4-cylinder engine didn’t go as smoothly as some might have imagined, according to Pete Gladysz, senior manager of powertrain for Chrysler’s Street and Racing Technology (SRT) group. “We had a lot of starts and stops in the program because we were trying to decide how close we were going to stay with our Global Engine Manufacturing Alliance partners [Mitsubishi and Hyundai], and it turned out they had a different set of requirements,” he says, noting Mitsubishi was set on developing a 2-liter engine for its Lancer Evo and Hyundai wanted a smaller displacement engine for its products. Chrysler, however, had a history with the 2.4-liter in the Neon SRT-4—which the Caliber SRT-4 is, essentially, a replacement for—and it wanted to build on that heritage. Speaking of the other two companies, he explains, “For them smaller motors are better, but when you look at the American customer, bigger”—as in displacement—“is better. So we decided about 2-1/2 years ago to go our separate ways,” Gladysz says.
Trying to design and engineer a unique engine for a relatively niche product like the Caliber SRT-4—volumes are expected to be limited to below 15,000, unless customer demand warrants additional investment in boosting turbo manufacturing capacity—poses significant business challenges. Gladysz says that his engineers worked with those in the mainstream powertrain group when the the high-volume naturally-aspirated 2.4-liter program commenced in order to make sure that every step was optimized for maximum efficiency from manufacturing through to engine performance for the performance group, as well.
While the SRT turbo and the conventional naturally-aspirated engines utilize the same cylinder block, the turbo requires improved water and oil flow. This meant manufacturing would have to machine separate water passages and oil squirters to assure reliable performance for the turbo. “We had to work with manufacturing right up front on this one, because if we did not have all the machining centers at the right spots on the machining line, it would have killed the whole engine program because we could not afford to machine our own block somewhere else,” Gladysz says. Besides the sharing of the block, the SRT team also carried over the standard engine’s forged crankshaft, oil pan, sensors and switches, throttle body, cam shaft and bearings, valvetrain valve cover, PCV, accessory drive and oil cooler.
Pistons—composed of high-copper eutectic aluminum alloy—and connecting rods with an increased bolt diameter for high clamp loads, were designed specifically for the turbo variant. The turbo also required a unique head gasket design with three functional layers, including a new fluorocarbon coating on the outermost surfaces for improved coolant, oil and combustion sealing. Engineers also had to develop a unique water pump for the SRT engine, complete with a smaller pulley diameter and a dual-port water inlet location for parallel cooling of the head and block. The oil pump had to be reengineered for higher capacities. Engineers went with a six lobe Gerotor (generated rotor) pump for its high-efficiency and quiet operation—the SRT-4’s pump operates at twice the engine speed and provides 25% higher flow and 23% higher pressure than would ordinarily be the case. The intake manifold was also redesigned to handle the higher injector pressure levels, while the exhaust manifold was uniquely designed and is produced with cast stainless steel for improved durability and higher temperature loads.
The turbocharger was developed by Mitsubishi (TD04HL4S-20) and features an Inconel turbine wheel and forged aluminum compressor wheel, which has been calibrated at 17,000 rpm with a wastegate position to provide optimum blend flow with turbine exist.
Not only did making changes only where necessary bring the SRT engine in at budget, but it also resulted in an engine that’s among the top performers in its class: 285-hp @ 5,700-6,400 rpm and 265 lb.-ft. of torque @ 2,000-5,600 rpm. Gladysz admits that SRT hoped to bring the engine power in at a more round number—Chrysler had said it planned to produce 300 horsepower from the 2.4-liter—although the engine is capable of achieving that level and more. “There’s a margin in this engine, but we had to create a total vehicle perception that met all of our goals. We are limiting boost in first and second gears today because you just literally would blow the tires off the car,” Gladysz contends. “We erred on giving the customer a car that is on the edge, but not over the edge. If we were building a race car we would have went over the edge, but this is not a race car. We haven’t tried to explore the upper limits of the motor, but I will tell you that some things may change down the road and we might make a different decision then.” For customers looking to modify their engines to reach the 300-plus horsepower level, Gladysz says the transmission and clutch are ready to handle the extra power without any major modifications. “We know that no matter what we do or what we say, the customer is going to modify these cars and we have built some margin into the parts for that.”
Chrysler’s SRT group started with the development of the Viper in 1992 along with the Plymouth Prowler roadster in 1997. The SRT badge has graced the decklids of the Dodge Neon, Chrysler Crossfire and Dodge Ram, all of which have been sent to pasture. The brand has spread to cover a majority of the Chrysler, Dodge and Jeep lineups, including the Chrysler 300 SRT-8, Dodge Magnum SRT-8, Jeep Grand Cherokee SRT-8, Dodge Charger SRT-8 and now the Caliber SRT-4.