## What Does DOHC Mean in Car Engines?
DOHC: Definition and Overview
DOHC stands for Double Overhead Camshaft, a configuration found in the cylinder head design of modern internal combustion engines. As the name suggests, it utilizes two camshafts positioned above the cylinder head, thereby controlling the opening and closing of intake and exhaust valves directly.
Advantages of DOHC Engines
**1. Improved Valve Timing Accuracy:**
Two separate camshafts ensure precise and independent control of intake and exhaust valve timing, optimizing engine performance and efficiency.
**2. Increased Horsepower and Torque:**
DOHC enables higher engine speeds by reducing valve train inertia, leading to increased horsepower and torque output.
**3. Reduced Emissions:**
Optimized valve timing allows for more efficient combustion, reducing exhaust gas emissions.
**4. Enhanced Fuel Economy:**
Improved combustion also contributes to enhanced fuel economy by reducing engine power losses.
DOHC Engine Construction
The DOHC configuration consists of:
**1. Cam Gears or Chains:**
The camshafts are driven by cam gears or chains connected to the crankshaft, ensuring synchronous operation.
**2. Rocker Arms or Finger Followers:**
Rocker arms or finger followers transmit the camshaft motion to the valve stems, opening and closing the valves.
DOHC vs. SOHC (Single Overhead Camshaft)
In contrast to DOHC engines, SOHC engines utilize a single camshaft positioned above the cylinder head. While SOHC engines are simpler and less expensive to manufacture, they offer less precise valve timing control and generally lower performance compared to DOHC.
DOHC vs. VTEC (Variable Valve Timing and Lift Electronic Control)
VTEC is a variable valve timing system developed by Honda that allows an engine to switch between different camshaft profiles for different engine speeds. This provides both improved low-end torque and high-end horsepower, while also enhancing fuel economy.
DOHC in High-Performance Engines
DOHC is a common feature in high-performance engines, where precise valve timing and high engine speeds are essential for achieving maximum output. It allows for:
**1. Higher Rev Limits:**
DOHC engines can operate at higher revolutions per minute (RPM) due to reduced valve train inertia.
**2. Optimized Valve Duration:**
The two camshafts enable the use of specific valve opening and closing durations for different engine operating conditions.
**3. Variable Valve Timing (VVT):**
Advanced DOHC designs incorporate VVT systems, allowing for dynamic adjustment of valve timing to optimize performance and fuel economy across a wider range of engine speeds.
Conclusion
DOHC engines provide significant advantages over SOHC counterparts, including improved valve timing accuracy, increased engine output, reduced emissions, and enhanced fuel economy. They are commonly found in high-performance engines and offer optimal valve control for maximizing engine performance.
