SOHC VTEC – What Kind of an Engine Is It? We Explain

Technology has evolved in a variety of ways over the years. This has aided automakers in improving and developing more advanced engines for their various brands. They have recently discovered more ways to make their engine lighter in weight while still providing excellent engine performance. SOHC is one engine design that has received a lot of attention.

The engine is well-known for its high efficiency. When compared to the old-style pushrod-driven overhead valve power plants, SOHC engines may generate an elevated engine speed, allowing for higher revolutions per minute (RPM). 

SOHC engines were adopted by racing cars prior to joining the VTEC family, dating back to the 1920s. The Bugatti manufacturers adopted the SOHC engine design to feature on the Type 35 Grand Prix.

Despite being used by prominent brands, the SOHC engine design did not enjoy an all-around recognition until the early 1980s. Since then, single overhead cam (SOHC) and double overhead cam (DOHC) engines have pushed OHV engines, which were the main engine producers at the time, into a sharp decline. However, the Honda manufacturers quickly adopted SOHC design to their VTEC engine models.

What is SOHC?

Overhead cams are designed with the camshaft placed over the cylinders. The term "single overhead cam (SOHC)" refers to a bank of cylinders, implying that the SOHC uses only one camshaft on the in-line engines. Two-cylinder banks are available on V pattern engine blocks, making it possible for the engine to feature a total number of two camshafts. 

This is a more efficient design than the traditional pushrod engines because it can rapidly control the valve's rocker arms. Aside from removing the weight capacity to 16 pushrods in V8 engines, less energy is lost in the SOHC design, which allows for faster crankshaft and camshaft RPMs.

The SOHC engine design is similar to other valve train arrangements. It has a belt or chain that runs from a gear on the crankshaft to the camshaft to keep the engine timing accurate.

However, there is a significant difference. The increased distance between the camshaft and crankshaft necessitates a longer timing belt or chain. The efficiency of a V pattern engine is a result of the control it gains from the two camshafts, which work with an additional timing chain.

Evolution of SOHC VTEC with Honda brand?

Honda is one of many well-known companies that have adopted the system for SOHC engines. The downside was that the Honda SOHC VTEC engines only used the VTEC system on the Honda intake valves. It is due to the fact that VTEC necessitates the addition of a third cam lobe and center rocker arm.

The spark plugs in the OHC engine are placed between two exhaust rocker arms, thus, consuming all the space for the VTEC's rocker arm to fit in. Furthermore, the exhaust and the intake cannot use the camshaft's center lobe, thus narrowing the VTEC attribute to one side.

When the J37A4 3.7L single overhead cam V6 engine was introduced in 2009, it ushered in a new era for SOHC VTEC. The invention began with the production of Acura TL AWD models. They adjusted the SOHC VTEC to accommodate exhaust and intake valves this time.

The SOHC VTEC exhaust and intake rocker shafts each have two exhaust and intake rocker arms. The first is referred to as the primary rocker arm. This rocker arm houses the VTEC switching piston, while the secondary rocker arm houses the return spring.

During low-revolution-per-minute engine operation, the primary rocker arm makes contact with a low-profile camshaft lobe. When VTEC is engaged, oil pressure from the exhaust rocker shaft forces the VTEC switching piston to enter the secondary exhaust rocker arm. This activity will make the VTEC lock the two exhaust rocker arms together, thus, working effectively. 

The high-profile camshaft lobe, which is designed to make contact with the secondary rocker arm during low-RPM engine operation, is capable of moving the two exhaust rocker arms altogether. The intake rocker shaft operates similarly, the only difference is that the high-profile camshaft lobe controls the primary rocker arm.

SOHC Engine Advantages Over DOHC Engines

A SOHC valve train is essentially a simplified version of the sophisticated DOHC valve train. A dual overhead cam engine, as the name implies, uses two camshafts bank of cylinders to control valve control, adding weight to the engine. However, because only one camshaft is located on the combustion cylinder, the spark plug is deprived of a perfect location for fostering the compressed fuel or air mixture.

A single overhead cam engine has a technical advantage over dual overhead cam (DOHC) setups with lower-end torque delivery due to lighter valve train weight.

The single overhead cam (SOHC) configuration is highly regarded as technologically friendly and provides modern engine builders with a considerable measure of efficiency freedom.

Many engine designers want to go from two valves producing the advanced multiple intakes and exhaust valves per cylinder. This is not just to follow a trend, but because the multiple exhaust and intake have proven to be more effective when it comes to engine efficiency. 

Using two smaller, lighter valves instead of a single valve reduces the resistance and enhances the valve train's effectiveness. Single overhead valve engines, which are extremely difficult to achieve with pushrod engines, can have about four valves in each cylinder.

Variable valve timing is simple in both single overhead cam (SOHC) and dual overhead cam (DOHC) engines. Honda's VTEC system, which was originally designed for dual overhead cam engines, was later rebuilt to work with single overhead cam (SOHC) engines. Due to size parameters within the cylinder head, the VTEC valve timing can only be used on the intake valve in this configuration.

The J37A4's novel intake rocker arm design eliminates the problem of incorporating a SOHC engine with a VTEC with regards to the exhaust and intake valve inconveniences that were normally encountered. 

On the J37A4, primary and secondary exhaust rocker arms correspond to each exhaust valve. As a result, the engine has twelve primary and secondary exhaust rocker arms. Each secondary intake rocker arm, on the other hand, is shaped like a "Y," allowing it to touch two intake valves at the same time. 

What SOHC Engines are currently in Production?

Honda VTEC engines popularized the single overhead cam. SOHC VTEC is currently the most popular SOHC design. The Ford Modular engines, which power the Mercury Grand Marquis and the Ford Mustang, are the technology champions, with 2 and 3-valve versions. Ford had previously produced a limited number of set single overhead cam 427 V8 engines with pushrod drivetrains commonly associated with American muscle engines to contend with Chrysler's HEMI engine.

Ford is not the only major automaker to use the SOHC engine design. Mercedes-Benz, for example, has adopted the single overhead cam setup in its V12 engines, which are available in the S Class: S65 and SL65 AMG. This was due to the company's desire to reduce engine weight and enable the vehicles to move more efficiently than their predecessors. The Mercedes-Benz single overhead cam V12 engine produces 510 and 604 horsepower.

What does the future hold for SOHC engines?

It is no longer secret that most automakers have adopted the dream of going electrical. And people are subscribed to the opinion that the invention of electric vehicle will dominate the market in 2050 and the SOHC engine, which has been in use for more than a century, will be wiped out of the market. 

However, some believe these engines might still be active in the market for at least 50 years. This is because some automakers are settling for hybrid engines over electric engines for some reasons. In addition, the cost of owning an electric car is on the high side, and this will be difficult to wipe the SOHC combustion engine out of the market because it is a cheaper alternative. 

Final thoughts

The SOHC VTEC is undoubtedly a gain for Honda manufacturers. This is because the engine offers an effective result and weighs lesser than other engine designs. The simplicity and productivity of the SOHC VTEC have attracted other prominent automakers like Ford and Mercedes Benz to adopt the SOHC design. 

Frequently Asked Questions (FAQs)

• Are SOHC engines good?

SOHC engines have greater low-end torque. When a SOHC engine is built with 16 valves, the engine produces more torque at low speeds. However, performance is significantly lower, especially at high speeds. It is less expensive because the engine comes with a single cylindrical rod that controls the exit and intake gases.

• How will I know if my car engine is SOHC or DOHC?

By looking at it, you can tell whether your vehicle's engine is SOHC or DOHC. The SOHC engine has a single camshaft, whereas the DOHC engine has two camshafts above the engine's head.

• Why should I choose a SOHC engine?

The SOHC engine has several benefits over the cam-in-block design, including the vehicle's engine Valves can be placed to optimize combustion chamber design. Multiple valves can be used, with up to five in each combustion chamber. A double spark plug can also be used.