Motor For 2007 Nissan Altima
The 2007 Nissan Altima offered buyers a choice of two distinct engines, each designed to provide a balance of performance and fuel economy. Understanding the nuances of these powertrains is key to appreciating the engineering that went into this popular sedan.
QR25DE: The Inline-Four Workhorse
The standard engine in the 2007 Altima was the QR25DE, a 2.5-liter inline-four cylinder engine. This engine belonged to Nissan's QR engine family, known for its robust design and relatively high power output for its displacement. Let's delve into its core components and functionality:
Engine Block and Internals
The QR25DE featured an aluminum alloy cylinder block, a common choice for modern engines due to its lightweight properties, which contribute to improved fuel efficiency and handling. The cylinder block housed cast iron cylinder liners to provide a durable wear surface for the pistons. This combination of materials offered a good balance between weight reduction and longevity.
Inside the cylinders resided lightweight aluminum pistons, connected to a forged steel crankshaft via connecting rods. The crankshaft was supported by five main bearings, ensuring smooth and stable rotation even under high stress. Forged steel provides significantly increased strength when compared to cast steel, allowing the engine to reliably handle the stresses of frequent use. The careful balancing of the rotating assembly (crankshaft, connecting rods, and pistons) was crucial for minimizing vibrations and ensuring smooth engine operation.
Cylinder Head and Valvetrain
The cylinder head of the QR25DE was also made of aluminum alloy, contributing to further weight reduction. It featured a dual overhead camshaft (DOHC) design, meaning that two camshafts controlled the intake and exhaust valves separately. This configuration allowed for more precise valve timing and control, resulting in improved engine performance and efficiency compared to older single overhead camshaft designs.
The valvetrain incorporated Nissan's Continuously Variable Valve Timing Control System (CVTCS) on the intake camshaft. CVTCS adjusted the intake valve timing based on engine speed and load, optimizing the engine's volumetric efficiency across the rev range. This resulted in better low-end torque and improved high-end horsepower. Specifically, CVTCS alters the phasing of the intake camshaft relative to the crankshaft. At low RPM, the intake valves open slightly later, reducing overlap and increasing cylinder pressure for better torque. At high RPM, the intake valves open earlier, increasing overlap and improving cylinder filling for enhanced horsepower. The exhaust valves used fixed valve timing on this engine.
The QR25DE utilized four valves per cylinder (two intake and two exhaust), further enhancing airflow and improving engine breathing. This design allowed for a greater total valve area compared to two-valve designs, leading to better cylinder filling and exhaust scavenging.
Fuel and Ignition Systems
The QR25DE employed a sequential multi-port fuel injection (SMPI) system. Each cylinder had its own fuel injector positioned in the intake manifold, spraying fuel directly into the intake port just ahead of the intake valve. This precise fuel delivery contributed to improved fuel efficiency and reduced emissions compared to older throttle-body injection systems. The fuel injectors were controlled by the engine control unit (ECU), which precisely metered the fuel based on various sensor inputs, such as engine speed, load, and air temperature.
The ignition system was a distributorless ignition system (DIS), also known as coil-on-plug (COP). Each cylinder had its own individual ignition coil mounted directly on top of the spark plug. This eliminated the need for a distributor and spark plug wires, resulting in a more reliable and efficient ignition system. The ECU controlled the firing of each ignition coil independently, ensuring precise ignition timing for optimal combustion.
Engine Management System
The entire operation of the QR25DE was overseen by a sophisticated engine control unit (ECU). The ECU constantly monitored various engine parameters through a network of sensors, including:
- Mass Airflow Sensor (MAF): Measures the amount of air entering the engine.
- Throttle Position Sensor (TPS): Indicates the position of the throttle plate.
- Crankshaft Position Sensor (CKP): Monitors the position and speed of the crankshaft.
- Camshaft Position Sensor (CMP): Monitors the position of the camshaft(s).
- Oxygen Sensors (O2): Measure the oxygen content in the exhaust gas.
- Coolant Temperature Sensor (CTS): Monitors the temperature of the engine coolant.
Based on these sensor inputs, the ECU adjusted fuel injection timing, ignition timing, and valve timing (via CVTCS) to optimize engine performance, fuel economy, and emissions. The ECU also performed diagnostic functions, monitoring the engine for faults and storing diagnostic trouble codes (DTCs) if a problem was detected.
The QR25DE in the 2007 Altima produced approximately 175 horsepower and 180 lb-ft of torque. While not a powerhouse, it offered a good balance of performance and fuel efficiency for everyday driving.
VQ35DE: The V6 Option
For drivers seeking more power, the 2007 Altima offered the VQ35DE, a 3.5-liter V6 engine. This engine belonged to Nissan's acclaimed VQ engine family, which has consistently earned recognition for its smooth operation, robust performance, and reliability. Here's a breakdown of its key features:
Engine Block and Internals
Like the QR25DE, the VQ35DE featured an aluminum alloy cylinder block, but in a V configuration, with two banks of three cylinders arranged at a 60-degree angle. This V configuration resulted in a shorter and more compact engine compared to an inline-six, contributing to better packaging within the engine bay. The VQ35DE also utilized cast iron cylinder liners for improved wear resistance.
The internal components of the VQ35DE were similar to the QR25DE, including aluminum pistons, forged steel connecting rods, and a forged steel crankshaft. However, the VQ35DE's crankshaft was supported by seven main bearings, providing even greater stability and smoothness compared to the four-cylinder engine.
Cylinder Heads and Valvetrain
The VQ35DE featured dual overhead camshafts (DOHC) for each cylinder bank, totaling four camshafts in all. This allowed for independent control of the intake and exhaust valves for each cylinder, enabling even more precise valve timing and control compared to the QR25DE.
Importantly, the VQ35DE incorporated CVTCS on both the intake and exhaust camshafts. This dual CVTCS system provided even greater flexibility in valve timing adjustment, allowing the ECU to optimize engine performance, fuel economy, and emissions across a wider range of operating conditions. By independently adjusting both intake and exhaust valve timing, the ECU could fine-tune the engine's volumetric efficiency and internal exhaust gas recirculation (EGR) rate, further enhancing its performance and efficiency.
Like the QR25DE, the VQ35DE utilized four valves per cylinder (two intake and two exhaust). This design contributed to improved airflow and cylinder filling, resulting in enhanced power output.
Fuel and Ignition Systems
The VQ35DE also employed a sequential multi-port fuel injection (SMPI) system, with each cylinder receiving fuel from its own dedicated fuel injector. This system provided precise fuel delivery for optimal combustion.
The ignition system was also a distributorless ignition system (DIS) with coil-on-plug (COP) technology. Each cylinder had its own individual ignition coil mounted directly on the spark plug, providing a strong and reliable spark.
Engine Management System
The VQ35DE was controlled by a sophisticated ECU that monitored various engine parameters through a network of sensors, similar to the QR25DE. The ECU used these sensor inputs to adjust fuel injection timing, ignition timing, and valve timing (via dual CVTCS) to optimize engine performance, fuel economy, and emissions.
The VQ35DE in the 2007 Altima produced approximately 270 horsepower and 258 lb-ft of torque. This significantly higher power output provided a noticeable improvement in acceleration and overall driving performance compared to the QR25DE.
The VQ35DE's advanced features, such as dual CVTCS and a robust V6 design, made it a standout engine in its class.
Conclusion
Both the QR25DE and VQ35DE engines offered in the 2007 Nissan Altima represented a commitment to delivering reliable and efficient power. While the QR25DE provided a solid foundation with its inline-four configuration and single CVTCS, the VQ35DE elevated the driving experience with its smooth V6 architecture and dual CVTCS, showcasing Nissan's engineering prowess in engine design. Understanding the technical details of these engines allows for a deeper appreciation of the 2007 Altima's performance and overall engineering.