The Importance of Valve Timing and Lift in Engine Performance

Valve timing and lift are crucial components in engine performance, and understanding how they work is essential for optimizing engine efficiency and power output. In this article, we will explore the concept of valve timing and its impact on engine performance, as well as the different techniques used to control valve timing.

**Understanding Valve Timing**

Valve timing refers to the relationship between the opening and closing of the intake and exhaust valves in relation to the movement of the piston. Proper valve timing is critical for ensuring that the engine is running efficiently and effectively. When the intake valve opens, it allows air and fuel into the cylinder, while the exhaust valve closes, allowing the exhaust gases to escape. If the valve timing is off, the engine can suffer from reduced power output, decreased efficiency, and increased emissions.

**Controlling Valve Timing**

Engineers use various techniques to control valve timing, including hydraulic lash adjusters, camshaft actuators, and electronic throttle body controls. These systems allow for precise adjustment of valve timing, enabling engineers to optimize performance and efficiency. By carefully calibrating valve timing, engine builders can achieve significant improvements in power output, fuel efficiency, and emissions.

**The Role of Lift in Engine Performance**

Lift refers to the amount of air and fuel that enters the cylinder during the intake stroke. Proper lift is essential for ensuring that the engine is running efficiently and effectively. If the lift is too low, the engine will struggle to breathe, leading to reduced power output and decreased efficiency. On the other hand, if the lift is too high, it can lead to engine knock or pinging, which can cause significant damage.

**Techniques for Controlling Lift**

Engine builders use various techniques to control lift, including camshaft design, valve spring tension, and intake manifold design. By carefully designing these components, engineers can optimize lift and ensure that the engine is running efficiently and effectively. Additionally, many modern engines feature advanced technologies such as variable valve timing and lift systems, which enable precise control over lift and valve timing.

**Emissions Reduction**

One of the key benefits of controlling valve timing is emissions reduction. By optimizing valve timing, engine builders can reduce emissions by minimizing the amount of unburned fuel that enters the exhaust system. This can be achieved by closing the intake valve earlier in the stroke cycle, which reduces the amount of air and fuel entering the cylinder. Similarly, closing the exhaust valve later in the stroke cycle allows for more efficient combustion and reduced emissions.

**Idling and Low-Load Operation**

In low-load operation, such as idling, engineers often prioritize reducing pumping losses over maximizing power output. By closing the intake valve earlier, engine builders can reduce these losses and improve efficiency during low-load operation. This technique is particularly useful in urban driving, where engines are frequently operating at low loads.

**Exhaust Stroke Optimization**

During the exhaust stroke, engineers use various techniques to optimize valve timing and lift. One common approach is to open the exhaust valve later in the stroke cycle, allowing for more efficient combustion and reduced emissions. By trapping some of the inert gas in the combustion chamber during the intake stroke, engineers can reduce NOx emissions and improve overall engine performance.

**Conclusion**

Valve timing and lift are critical components in engine performance, and understanding how they work is essential for optimizing engine efficiency and power output. By carefully controlling valve timing and lift, engine builders can achieve significant improvements in power output, fuel efficiency, and emissions. Whether it's optimizing idling or low-load operation or exhaust stroke optimization, the techniques used to control valve timing are complex and require careful consideration.

**Additional Resources**

For more information on valve timing and lift, be sure to check out Humble Mechanic's YouTube channel, where Charles hosts a series of articles and tutorials on engine performance and tuning. Additionally, you can find detailed guides and tutorials on valve timing and lift adjustment at various online forums and communities.

Jason: Why would you close the intake valve early?

Charles: Let me tell you, you close the intake valve early this really has to do with situations where you're basically just idling or at super low load. So what's happening when you're just sitting there idling is you really don't need much air fuel to keep this engine idling and so you'll close that intake valve early effectively what you're doing is reducing the amount of pumping losses you have because that Piston's trying to pull in air and fuel you get enough you have enough for what you need to just idle the engine and then you close that intake valve early it continues to go down and you're no longer pulling on that vacuum and then you would have more pumping losses so from an efficiency standpoint it's just a smart thing to do when you're sitting there idling to close the intake valves early.

Jason: Why would you open the intake valve early?

Charles: Let me tell you why you open the intake valve early. So this means you're on your exhaust stroke so you're pushing out that exhaust gas and now you're opening that intake valve allowing for more air and fuel into the cylinder which can lead to a significant increase in power output but it also requires careful consideration of the engine's emissions.

Jason: How does the lift affect engine performance?

Charles: Lift refers to the amount of air and fuel that enters the cylinder during the intake stroke. Proper lift is essential for ensuring that the engine is running efficiently and effectively. If the lift is too low, the engine will struggle to breathe leading to reduced power output and decreased efficiency. On the other hand if the lift is too high it can lead to engine knock or pinging which can cause significant damage.

Jason: How do you control lift?

Charles: Engine builders use various techniques to control lift including camshaft design valve spring tension and intake manifold design. By carefully designing these components engineers can optimize lift and ensure that the engine is running efficiently and effectively. Additionally many modern engines feature advanced technologies such as variable valve timing and lift systems which enable precise control over lift and valve timing.

Jason: How does controlling valve timing affect emissions?

Charles: One of the key benefits of controlling valve timing is emissions reduction. By optimizing valve timing engine builders can reduce emissions by minimizing the amount of unburned fuel that enters the exhaust system. This can be achieved by closing the intake valve earlier in the stroke cycle which reduces the amount of air and fuel entering the cylinder. Similarly closing the exhaust valve later in the stroke cycle allows for more efficient combustion and reduced emissions.

Jason: What's the best way to optimize engine performance?

Charles: The best way to optimize engine performance is through careful consideration of valve timing and lift. By understanding how these components interact with one another engineers can achieve significant improvements in power output fuel efficiency and emissions. Whether it's optimizing idling or low-load operation or exhaust stroke optimization the techniques used to control valve timing are complex and require careful consideration.

**Additional Resources**

For more information on valve timing and lift be sure to check out Humble Mechanic's YouTube channel where Charles hosts a series of articles and tutorials on engine performance and tuning. Additionally you can find detailed guides and tutorials on valve timing and lift adjustment at various online forums and communities.

"WEBVTTKind: captionsLanguage: enhello everyone and welcome in this video we're going to be talking about variable valve lift and variable valve timing and to help explain this we have Charles Mr humble mechanic uh who brought some VW parts some Audi parts to help explain this so what is in front of me right now so these are cam shafts and a cam bridge out of an 09 Audi A4 this is almost the exact same setup that you'll find in the 15 and up Mark 7 GTI we have our exhaust cam with variable valve lift and we have our intake cam with variable valve timing sweet so yeah as you mentioned we've got our intake right here intake cam exhaust cam uh and the basics we're going to start here with the variable valve lift which is on the exhaust side and basically what you're doing you have two different cam profiles so you have this higher cam profile and then you have a little bit lower of a cam profile and you have an individual system for each cylinder so you can move this back and forth It's on a spline so you can move that and each individual cylinder has its own control and so Charles can you kind of explain the details of how this system actually moves back and forth to change that cam profile right so like Jason said these are essentially sleeves that are splined to the cam shaft we have two solenoids that will control this sleeve one solenoid will pull it one way the other solenoid will pull it the other way when the solenoid is activated the Pinal will come down and ride in this Channel and it'll actually slide that sleeve over to change the profile of the cam shaft that the rocker's riding on so if we are riding on our high lift this solenoid will activate it'll pull it over and that'll allow us to ride on our low lift when we're ready to go back to high lift this solenoid will activate pulling it the other way and allowing us to ride on the high lift profile of our Cam and of course this will have two valves per cylinder so you'll have a rocker here as well as a rocker here this is a pretty narrow rocker to be able to ride on both of those profiles and so kind of the interesting thing about this is that it's on the exhaust side and not the intake side you have one cam profile here on the intake side on the exhaust the reason uh for this this is a turbocharged engine and so you've got uh pressure pushing in air it's fairly easy to get that intake charge uh but it's then difficult to get all that air all that exhaust out and so once you get into the higher RPM at higher loads and you're burning all this air and fuel you want to open these exhaust valves a little bit more so it's easier to get that air out and you can create more power less losses more power uh so that's kind of the beauty of this vvl system right this will also improve throttle response a little bit and uh makes for a pretty fun car to drive yeah it's pretty sweet now just because this engine doesn't have this on the intake side doesn't mean you couldn't do that you could have two different cam profiles and use a very similar system on the intake side and you'd get that benefit of getting in more air once you're at higher RPM uh higher loads uh so you can make more more power um and you can also change the duration with the two cam lobes um so you were saying you noticed you know these are it's not just lift we're not just ra opening the valve more we're also opening it sooner and we're actually closing it a little bit before we would on the low lift but not very much so the duration is actually longer as well okay so much more time and lift for all that air to get out uh for efficiency and you know not not losing all that power and getting too much pressure going out your ex so very cool yeah that's all ECM controlled so the engine computer is going to do that based on the scenario the vehicle is in it in a lot of ways knows better than most of us on what it wants from the engine definitely Me Def better than me yeah I just poke at computer and yeah so moving along to the intake side uh this as you can see just a single cam profile and what we have here is our variable valve timing and so if I hold this stationary and you can see the chain won't move and we can advance it or pull timing back and the timing so as you can see on the intake there is only one cam profile and so all we're doing is let's say you know you have your cam profile open closed you're just shifting when it opens and closes back and forth and that's all you're doing the cam profiles remaining exactly the same so we're going to talk about why you would want to shift when the intake valve opens and closes uh but first let's take a look inside and see how this works so the variable valve timing is all based on oil pressure when the profile wants to change one way this well will fill up here and shift this way if it needs to shift the other way there's another port and it'll shift this way and then when it wants to bleed down the pressure there's actually a release or a relief hole right down here at the bottom then this oil will fall down the timing chain side and it'll reset back to zero cool so all you're doing I mean you've got this little you know complicated chamber that's sending out oil and you're doing is filling either one side with oil or the other side with oil they both have a port and then you can drain it out the back there that's it it's all controlled there's actually uh on the timing cover which goes in front of this there's a solenoid that goes there this is a spool valve like you said that has different chambers of and ways to pass oil through this there's actually another part to it right here that you guys don't need to know about so I don't know why I ped it up you know probably worth mentioning that when you're thinking about this this gear is remaining stationary I mean obviously it's spinning but the cam is rotating in relation to it the actual shaft is rotating not the cam gear so this is more what it would look like if you could get in there and see it in action so now we're going to talk about why you want to do this why you want to change the valve timing and so we're going to start with the example of a late intake valve closing so we're closing our intake valve later than usual so why would you do this well when you do that that means your cylinder is going to be starting to go back up to compress that air and your intake valve is still going to be open so you're going to push some of that air fuel mixture back out into the intake manifold now there are some pumping losses associated with that where you're going to reduce those pumping losses because you're now charging your intake manifold but really the main thing you're doing here is you're controlling how much air and fuel you have in that combustion chamber and in doing so how much uh combustion you're going to have how much you know power you're going to make and so you can reduce the temperature uh of that cylinder by using less air and Fuel and so by reducing that temperature you're going to have less nox emissions so the common theme of all these different scenarios of kind of choosing do you open the intake valve early or late or the exhaust valve do you you know do you close it late or early uh the common theme with all of these is going to have to relate to emissions right that's how that's how we look at it is and and it's mostly done by controlling temperature and therefore controlling nox emissions so Jason why would you close the intake valve early well Charles let me tell you you you close the intake valve early uh this really has to do with situations where you're basically just idling or at super low load so what's happening when you're just sitting there idling is you really don't need much air fuel to keep this engine idling and so you'll close that intake valve early and effectively what you're doing is reducing the amount of pumping losses you have because that Piston's trying to pull in air and fuel you get enough you have enough for what you need to just idle the engine and then you close that intake valve early it continues to go down and you're no longer pulling on that vacuum and then you would have more pumping losses so from an efficiency standpoint it's just a smart thing to do uh when you're sitting there idling to close the intake valves early so Jason why would you open the intake valve early well Charles let me tell you why you open the intake valve early so this means you're on your exhaust stroke so you're pushing out that exhaust gas and now you're opening that intake valve so what you're doing is you're pushing some of that inert gas that exhaust back into your intake manifold and this is kind of similar to the principle of like EGR why you would use an EGR system so that inert gas is in there that comes in you're controlling the temperature of combustion chamber once again uh to reduce nox emission it's all about the nox all about the nox yep so Jason why would you change the time when you close your exhaust valve well Charles let me tell you about closing exhaust valves so the important thing here once again comes back to noox emissions so if you close the exhaust valve early what you're doing is trapping some of that exhaust that inert gas in the combustion chamber and then when your intake stroke occurs you still have some of that inert gas in there and thus you know you're going to have lower combustion temperatures and lower nox emissions uh the other side if you want to close it later of course you can get all of that exhaust gas out of there so that you can fill it completely with fresh air and Fuel and get more power now obviously you don't want to open the exhaust valve early that's during your combustion stroke so you just be sending power out your exhaust and shooting flames which would be cool but you wouldn't be making any power out your wheels it is the peak of inefficiency and that's where like combining these two together really get interesting with with lift and timing cuz you can control way down way way down and what you're trying to get out of your engine super down out of your engine well thank you all for watching and Charles thank you uh once again for hosting me in your lovely garage and always supplying these great Parts uh it's always a pleasure and if you're not you should definitely check out humble mechanic on YouTube I'll include a link I'll put it over his face uh so that your face is blocked out and you should click that and subscribe to his channel and uh if you're not already subscribed to mine you should be and there's a bell now on YouTube uh have you heard about this you got to click the Bell you got to ring the bell the bell ring so that you get notifications otherwise you're like subscribed but you're not actually like subscribed it doesn't tell you when new stuff is outhello everyone and welcome in this video we're going to be talking about variable valve lift and variable valve timing and to help explain this we have Charles Mr humble mechanic uh who brought some VW parts some Audi parts to help explain this so what is in front of me right now so these are cam shafts and a cam bridge out of an 09 Audi A4 this is almost the exact same setup that you'll find in the 15 and up Mark 7 GTI we have our exhaust cam with variable valve lift and we have our intake cam with variable valve timing sweet so yeah as you mentioned we've got our intake right here intake cam exhaust cam uh and the basics we're going to start here with the variable valve lift which is on the exhaust side and basically what you're doing you have two different cam profiles so you have this higher cam profile and then you have a little bit lower of a cam profile and you have an individual system for each cylinder so you can move this back and forth It's on a spline so you can move that and each individual cylinder has its own control and so Charles can you kind of explain the details of how this system actually moves back and forth to change that cam profile right so like Jason said these are essentially sleeves that are splined to the cam shaft we have two solenoids that will control this sleeve one solenoid will pull it one way the other solenoid will pull it the other way when the solenoid is activated the Pinal will come down and ride in this Channel and it'll actually slide that sleeve over to change the profile of the cam shaft that the rocker's riding on so if we are riding on our high lift this solenoid will activate it'll pull it over and that'll allow us to ride on our low lift when we're ready to go back to high lift this solenoid will activate pulling it the other way and allowing us to ride on the high lift profile of our Cam and of course this will have two valves per cylinder so you'll have a rocker here as well as a rocker here this is a pretty narrow rocker to be able to ride on both of those profiles and so kind of the interesting thing about this is that it's on the exhaust side and not the intake side you have one cam profile here on the intake side on the exhaust the reason uh for this this is a turbocharged engine and so you've got uh pressure pushing in air it's fairly easy to get that intake charge uh but it's then difficult to get all that air all that exhaust out and so once you get into the higher RPM at higher loads and you're burning all this air and fuel you want to open these exhaust valves a little bit more so it's easier to get that air out and you can create more power less losses more power uh so that's kind of the beauty of this vvl system right this will also improve throttle response a little bit and uh makes for a pretty fun car to drive yeah it's pretty sweet now just because this engine doesn't have this on the intake side doesn't mean you couldn't do that you could have two different cam profiles and use a very similar system on the intake side and you'd get that benefit of getting in more air once you're at higher RPM uh higher loads uh so you can make more more power um and you can also change the duration with the two cam lobes um so you were saying you noticed you know these are it's not just lift we're not just ra opening the valve more we're also opening it sooner and we're actually closing it a little bit before we would on the low lift but not very much so the duration is actually longer as well okay so much more time and lift for all that air to get out uh for efficiency and you know not not losing all that power and getting too much pressure going out your ex so very cool yeah that's all ECM controlled so the engine computer is going to do that based on the scenario the vehicle is in it in a lot of ways knows better than most of us on what it wants from the engine definitely Me Def better than me yeah I just poke at computer and yeah so moving along to the intake side uh this as you can see just a single cam profile and what we have here is our variable valve timing and so if I hold this stationary and you can see the chain won't move and we can advance it or pull timing back and the timing so as you can see on the intake there is only one cam profile and so all we're doing is let's say you know you have your cam profile open closed you're just shifting when it opens and closes back and forth and that's all you're doing the cam profiles remaining exactly the same so we're going to talk about why you would want to shift when the intake valve opens and closes uh but first let's take a look inside and see how this works so the variable valve timing is all based on oil pressure when the profile wants to change one way this well will fill up here and shift this way if it needs to shift the other way there's another port and it'll shift this way and then when it wants to bleed down the pressure there's actually a release or a relief hole right down here at the bottom then this oil will fall down the timing chain side and it'll reset back to zero cool so all you're doing I mean you've got this little you know complicated chamber that's sending out oil and you're doing is filling either one side with oil or the other side with oil they both have a port and then you can drain it out the back there that's it it's all controlled there's actually uh on the timing cover which goes in front of this there's a solenoid that goes there this is a spool valve like you said that has different chambers of and ways to pass oil through this there's actually another part to it right here that you guys don't need to know about so I don't know why I ped it up you know probably worth mentioning that when you're thinking about this this gear is remaining stationary I mean obviously it's spinning but the cam is rotating in relation to it the actual shaft is rotating not the cam gear so this is more what it would look like if you could get in there and see it in action so now we're going to talk about why you want to do this why you want to change the valve timing and so we're going to start with the example of a late intake valve closing so we're closing our intake valve later than usual so why would you do this well when you do that that means your cylinder is going to be starting to go back up to compress that air and your intake valve is still going to be open so you're going to push some of that air fuel mixture back out into the intake manifold now there are some pumping losses associated with that where you're going to reduce those pumping losses because you're now charging your intake manifold but really the main thing you're doing here is you're controlling how much air and fuel you have in that combustion chamber and in doing so how much uh combustion you're going to have how much you know power you're going to make and so you can reduce the temperature uh of that cylinder by using less air and Fuel and so by reducing that temperature you're going to have less nox emissions so the common theme of all these different scenarios of kind of choosing do you open the intake valve early or late or the exhaust valve do you you know do you close it late or early uh the common theme with all of these is going to have to relate to emissions right that's how that's how we look at it is and and it's mostly done by controlling temperature and therefore controlling nox emissions so Jason why would you close the intake valve early well Charles let me tell you you you close the intake valve early uh this really has to do with situations where you're basically just idling or at super low load so what's happening when you're just sitting there idling is you really don't need much air fuel to keep this engine idling and so you'll close that intake valve early and effectively what you're doing is reducing the amount of pumping losses you have because that Piston's trying to pull in air and fuel you get enough you have enough for what you need to just idle the engine and then you close that intake valve early it continues to go down and you're no longer pulling on that vacuum and then you would have more pumping losses so from an efficiency standpoint it's just a smart thing to do uh when you're sitting there idling to close the intake valves early so Jason why would you open the intake valve early well Charles let me tell you why you open the intake valve early so this means you're on your exhaust stroke so you're pushing out that exhaust gas and now you're opening that intake valve so what you're doing is you're pushing some of that inert gas that exhaust back into your intake manifold and this is kind of similar to the principle of like EGR why you would use an EGR system so that inert gas is in there that comes in you're controlling the temperature of combustion chamber once again uh to reduce nox emission it's all about the nox all about the nox yep so Jason why would you change the time when you close your exhaust valve well Charles let me tell you about closing exhaust valves so the important thing here once again comes back to noox emissions so if you close the exhaust valve early what you're doing is trapping some of that exhaust that inert gas in the combustion chamber and then when your intake stroke occurs you still have some of that inert gas in there and thus you know you're going to have lower combustion temperatures and lower nox emissions uh the other side if you want to close it later of course you can get all of that exhaust gas out of there so that you can fill it completely with fresh air and Fuel and get more power now obviously you don't want to open the exhaust valve early that's during your combustion stroke so you just be sending power out your exhaust and shooting flames which would be cool but you wouldn't be making any power out your wheels it is the peak of inefficiency and that's where like combining these two together really get interesting with with lift and timing cuz you can control way down way way down and what you're trying to get out of your engine super down out of your engine well thank you all for watching and Charles thank you uh once again for hosting me in your lovely garage and always supplying these great Parts uh it's always a pleasure and if you're not you should definitely check out humble mechanic on YouTube I'll include a link I'll put it over his face uh so that your face is blocked out and you should click that and subscribe to his channel and uh if you're not already subscribed to mine you should be and there's a bell now on YouTube uh have you heard about this you got to click the Bell you got to ring the bell the bell ring so that you get notifications otherwise you're like subscribed but you're not actually like subscribed it doesn't tell you when new stuff is out\n"