The timing system in a vehicle is responsible for ensuring that the engine fires properly. In this instance, variable valve timing, or VVT for short, is used primarily for emissions control and performance. Over the years, manufacturers have developed several different designs and technologies related to this system to help control the timing and impact how long the exhaust and intake valves remain open.
There may be other actions that occur during this process. The system might rotate the camshaft either forward or by slowing it. Making adjustments in the overlap time between when the intake valve opens and the exhaust valve closes can help improve your engine efficiency. The whole system seems complex at first, but it’s not really that difficult to understand.
First, let’s take a look at this graphic from Car and Driver that shows what a VVT engine looks like.
Variable Valve Timing, Car and Driver, 2021
Variable valve timing is responsible for controlling three elements of the intake and exhaust valves. It’s responsible for valve timing, or when the valves open and close based on the points in the piston’s movement. Then, there’s the duration, which refers to how long the valves remain open (or closed). Finally, VVT also affects the valve lift, which is how far the valves actually open.
In order to monitor all of this, various sensors are responsible for feeding information to the ECU, or the computers onboard. In addition to sensors, there are physical mechanisms that help control the characteristics and behavior of the valves. The engine needs to monitor timing in order to handle all the variables of combustion, and without a conventional time scale, you can see just how quickly things actually move when you fire up the engine.
When you add in modern electronics, controls to optimize valve events, and premium fuel injection, it all comes down to precision that can’t be more than a millisecond off or it could ruin the entire engine’s operation.
The system is comprised of gears that are placed one inside the other, an inner gear that connects to the camshaft, and an outer gear that connects to the chain or drive belt. When normal driving conditions are engaged, the cogs are meshed together and turn at the same rate. However, oil pressure makes it easy to separate the gears, allowing them to change their relative speeds and help change the speed of the camshaft.
When you adjust the valve gears and controls, the adjustment will change the duration of valve lifts, which are responsible for controlling the intake and exhaust. Below, you’ll see the two main types of VVT engines and what each entails.
Essentially, the dual VVT system creates a solution that helps the engine breathe more efficiently. By adjusting the timing of the valves, you can generate more power, better fuel efficiency, and even reduced emissions. It also offers greater torque at low speeds without the risk of engine knocking. At high speeds, you’ll enjoy premium horsepower without the excess noise and vibrations that some older vehicles have.
Dual VVT also offers reduced emissions at the same time it’s providing you with excess power, so it gives you the best of both worlds. Even a single VVT, though, can be an economical upgrade to help save on fuel emissions and help the engine “breathe” more effectively.
The VVT has an economy profile (below 6,000 rpm) and a performance profile (over 6,000 rpm). When the VVT activates, oil pressure will be exerted on an actuator that presses the camshaft slightly, helping engage the “performance” setting. With dual or single timing, the same thing happens. In a dual system, the exhaust valves are activated in addition to the intake, which helps minimize stop/start pressures and ensures premium performance.
Adjusting the overlap sequences between your intake and exhaust valves also allows you to enjoy maximum scavenging of the intra-cylinder charge. High RPM and tremendous power combine to deliver impressive low-end torque that’s just as impressive as the performance that you’re getting.
Ignition timing is another part of this equation. This usually advances during the lighter load operations so that lean air-fuel mixtures don’t create knocks in the engine. This timing all happens in such short order that you can’t actually see it in action unless you’ve got the vehicle torn apart and know what you’re looking for. The spark occurs at a point between 0.002 seconds and 0.0002 seconds, which is 10 to 100 times faster than a single hummingbird wing flap.
When the engine is cold, timing can be delayed and late fuel injection is designed to be combined with earlier valve openings so that the catalytic converter can reach operating temperature more effectively.
Now that you have a better idea of how this feature works on your vehicle, let’s talk about the advantages that come from having this system in place:
This offers a much better solution than former methods, helping deliver premium power and efficiency all at once. Essentially, with a well-designed VVT system, you will get better fuel economy and lower emissions while still getting higher RMP and better power. Plus, when it’s all done properly, it can increase the lifespan of your engine compared to older models that used other methods for valve timing.
As with any of your vehicle’s systems, there are certain error codes and issues that are known to occur when it comes to the VVT system. The most common engine codes are:
Generally, these two error codes will let you know that something is wrong with your variable valve timing system and that it needs to be replaced. Aside from the valve timing being off, other problem areas include:
There are a number of things that can lead to problems with your VVT system. Dirty oil and sludge buildup can result in poor operation of the system. If left unchecked, it can eventually lead to cam failure. That’s why maintenance is such an important part of having this system.
If you do not keep up with oil changes, you could see anything from simple timing issues to a total system failure, depending on how long you let things go. A drop in oil pressure or a damaged sensor could also cause issues, as they prevent the system from operating at its peak performance.
The biggest thing to note with VVT is that there are virtually no drawbacks—you get all the perks without the concessions and you’re never going to have to compromise on efficiency to get the power that you need.
With variable valve timing, the engine no longer has an EGR valve. The Exhaust Gas Recirculation valve has become obsolete in vehicles with VVT, which controls the timing of the gasses and their release, including saving the inert gas for the next combustion cycle. It also helps by controlling the temperature of combustion and the production of those nitrous oxides in the first place.
A lack of regular oil changes can lead to a poorly lubricated system that doesn’t work properly. The VVT needs clean oil more than anything, so a lack of regular oil changes could quickly lead to serious damage if you’re not careful. You could cause issues with the VVT chain, the solenoid, or even the gear drive. Check your oil regularly, because low oil levels can also create problems with your variable valve timing system.
Newer systems also use continuous variable valve timing, or CVVT, which is digitally controlled by your ECU in the engine. This optimizes the valve timing at all speeds and for all engine conditions. There are different mechanisms and setups in every engine, but generally, CVVT occurs using solenoid valves and a variable timing camshaft, along with a flexible hydraulic connection to the sprocket.
An important note here: unless you’re a car enthusiast that works on your own vehicles and has extensive knowledge of engine operation, VVT issues are something that is generally best left to the professionals. Fixing these issues is a combination of tinkering with timing and checking the computer system for proper operation, and it can be tricky to diagnose and repair the issue if you’re not familiar with the systems.
If you do know how to handle your own engine timing, that’s great. However, be sure that you don’t get in over your head, and feel free to reach out to the pros if you want a little extra assistance. You don’t necessarily have to go to a dealership, but find a repair shop or service center that can help you with all of the timing issues on your engine.
While VVT systems are fairly similar from one vehicle to the next, they aren’t identical. Furthermore, some manufacturers are coming up with their own trademarked VVT systems, so you’ll need to take the time to research your specific make and model, as well as the timing system that is in place. The way that a system works in a BMW is going to be quite different than in a Toyota, in many cases.
VVT is used by most car makers, including the likes of:
Understanding your vehicle’s specific needs when it comes to the VVT system is a large part of vehicle ownership. Anytime you sense that something doesn’t feel right or that maybe performance is lacking, consider whether your VVT system is up to snuff. If you haven’t lately, get an oil change and have the engine oil pressure checked to make sure everything is operating as it should.
If you want to ensure that your VVT is properly cared for, make sure that you find an independent shop or mechanic that can help you with all of your needs. Consider whether the mechanics have experience with your type of VVT system or your make and model of vehicle, too, because each system is a little different.
Typically, however, today’s mechanics are well-versed in these systems and they know how to keep them functioning properly. If you’re in the market for something more than an oil change, you’ll be able to trust that they will take care of you, even when you can’t figure out what’s wrong on your own. VVT is a topic that’s often talked about in performance and racing circles, but it’s something that every driver can benefit from if they know what it is and how to use it.
It’s the 21st century and computers are changing everything we do. While all the new upgrades may make it seem like there’s some kind of “magic” happening when you run your engine, it’s not magic. It’s just technology, and it’s a technology that is helping people in several ways.
VVT has reached a compromise between power and performance and the risk of higher emissions, by doing its part to reduce the emissions that come out of the engine while also helping improve the engine’s operation. It’s a complex system, but once you understand how it works and what it does, you’ll have a much better appreciation for it and you’ll be sure to keep it in the best condition possible.
Resourceshttps://www.austincc.edu/wkibbe/vvt.htm https://www.caranddriver.com/news/a15341425/variable-valve-timing-explained-an-appreciation-of-how-quickly-engines-operate/ https://carbiketech.com/vvt-variable-valve-timing/ https://dannysengineportal.com/vvt-i-variable-valve-timing-how-does-it-work/