How does cam timing work for a car?
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Kinda like a wind up music box does. Spin rod that has dimples in different places along it. Those dimples open and close valves rather than hitting metal tines that make sounds.
Kinda like a wind up music box does. Spin rod that has dimples in different places along it. Those dimples open and close valves rather than hitting metal tines that make sounds.
Cams are rods that are ground in a manner where they have a lobe on them. As the rod spins the lobe pushes on a rod that opens and closes a valve. There’s 2 things you can adjust on the lobe profile.
1. How tall the lobe (lift) is which changes how much the valve is open at it’s fully open position.
2. Duration, which is how long the valve stays open.
These 2 features are permanently part of the cam profile and can’t be changed (as the cam wears down the amount of lift gets shorter). Newer engines can adjust lift by using 2 cam profiles. 1 cam profile is used for low RPM and low load while a second lobe profile is used at high RPMs high load.
Timing is adjusting when the valve opens and closes in relation to where the piston is through a process called phasing. They normally use a system that controls oil pressure that advances the cam gear a few degrees forward or retards it a few degrees back to adjust when the valves open and close. [Here is an example of Toyota’s system called VVTI](https://www.youtube.com/watch?v=YjIKUrre4FQ) other manufacturers have similar systems like Honda’s VTEC or BMW’s VANOS. I’m pretty sure every car manufacturer has a version these days.
Cams are rods that are ground in a manner where they have a lobe on them. As the rod spins the lobe pushes on a rod that opens and closes a valve. There’s 2 things you can adjust on the lobe profile.
1. How tall the lobe (lift) is which changes how much the valve is open at it’s fully open position.
2. Duration, which is how long the valve stays open.
These 2 features are permanently part of the cam profile and can’t be changed (as the cam wears down the amount of lift gets shorter). Newer engines can adjust lift by using 2 cam profiles. 1 cam profile is used for low RPM and low load while a second lobe profile is used at high RPMs high load.
Timing is adjusting when the valve opens and closes in relation to where the piston is through a process called phasing. They normally use a system that controls oil pressure that advances the cam gear a few degrees forward or retards it a few degrees back to adjust when the valves open and close. [Here is an example of Toyota’s system called VVTI](https://www.youtube.com/watch?v=YjIKUrre4FQ) other manufacturers have similar systems like Honda’s VTEC or BMW’s VANOS. I’m pretty sure every car manufacturer has a version these days.
The cam has an adjustable ‘relative angle’ compared to the crank position
In oldschool non-VVT engines it is simpler because the cam only has one fixed position relative to the crank. This can be adjusted, but it stays fixed and does not vary while the car is running. A belt or chain links them so they rotate together.
In newer cars with vvt it is more complicated because the cam angle relative to the crank changes and varies while the car is running, improving efficiency. A ‘phaser’ is often used to adjust the relative cam angle while running. This makes it more complicated to understand at first.
Try to understand oldschool non-VVT first and then VVT afterwards. Trying to understand vvt before non-vvt would be very hard.
For example, just look up a simple oldschool engine like a 351w or a 350 SBC. The cam literally just rotates along with the crank at a fixed position. You can shift the angle, but you only get to pick one angle.
Then compare to the similar but newer LS with vvt and phasers
If the cam is not adjusted properly the valves will be opening/closing at the wrong time relative to the pistons. Making adjustments to the timing can improve performance for specific applications.
In it’s simplest form on stock oldschool non-VVT it’s really easy you just line the cam and the crank up at the default factory setting hopefully marked on the engine. If the mechanic/manufacturer before you was friendly they would mark it so you don’t have to fuck around. And if it gets shifted off because of a slipping belt or something you just reset it back to the markings. But it can get super complicated with vvt and high performance tuning.
The cam has an adjustable ‘relative angle’ compared to the crank position
In oldschool non-VVT engines it is simpler because the cam only has one fixed position relative to the crank. This can be adjusted, but it stays fixed and does not vary while the car is running. A belt or chain links them so they rotate together.
In newer cars with vvt it is more complicated because the cam angle relative to the crank changes and varies while the car is running, improving efficiency. A ‘phaser’ is often used to adjust the relative cam angle while running. This makes it more complicated to understand at first.
Try to understand oldschool non-VVT first and then VVT afterwards. Trying to understand vvt before non-vvt would be very hard.
For example, just look up a simple oldschool engine like a 351w or a 350 SBC. The cam literally just rotates along with the crank at a fixed position. You can shift the angle, but you only get to pick one angle.
Then compare to the similar but newer LS with vvt and phasers
If the cam is not adjusted properly the valves will be opening/closing at the wrong time relative to the pistons. Making adjustments to the timing can improve performance for specific applications.
In it’s simplest form on stock oldschool non-VVT it’s really easy you just line the cam and the crank up at the default factory setting hopefully marked on the engine. If the mechanic/manufacturer before you was friendly they would mark it so you don’t have to fuck around. And if it gets shifted off because of a slipping belt or something you just reset it back to the markings. But it can get super complicated with vvt and high performance tuning.
A camshaft is a spinning rod with lobes on it. Those lobes determine **when** the valves open and close. If the lobes are tall and narrow (pointy?) then they will push the valve really far open for a short period of time. If they are short and wide, the valve will only open a little bit, but for a longer period of time. Every engine is slightly different in what it needs.
The “when” is really important. Cars use a 4-stroke engine (suck, squeeze, bang, blow). You want the intake valves to be open for the first down-stroke, and closed for the other 3. You also want the exhaust valves to be open on the last up-stroke, and closed for the other 3. If any of the valves are open when the piston is near the top, they might hit the piston and cause damage. While opening on the right stroke is pretty easy, the fine-tuning of how much air to let in, and how much exhaust to leave in for proper emissions/combustion-mix is much harder.
And that’s where variable valve timing comes in. Most cars sold to the public have a camshaft designed with a smooth, quiet idle and decent efficiency. But they can improve performance if they open the intake valve early to let in more air. The problem is that if they let in too much air at idle, the RPMs will increase on their own (not safe) or they have to cut ignition which makes for a loud choppy idle. If they use the “mild” cam and adjust it back and forward, they can get the best of both worlds. The VVT is a device (driven by oil pressure or an electronic motor) at the end of the camshaft that can rotate it forward or backward to make this adjustment.
A camshaft is a spinning rod with lobes on it. Those lobes determine **when** the valves open and close. If the lobes are tall and narrow (pointy?) then they will push the valve really far open for a short period of time. If they are short and wide, the valve will only open a little bit, but for a longer period of time. Every engine is slightly different in what it needs.
The “when” is really important. Cars use a 4-stroke engine (suck, squeeze, bang, blow). You want the intake valves to be open for the first down-stroke, and closed for the other 3. You also want the exhaust valves to be open on the last up-stroke, and closed for the other 3. If any of the valves are open when the piston is near the top, they might hit the piston and cause damage. While opening on the right stroke is pretty easy, the fine-tuning of how much air to let in, and how much exhaust to leave in for proper emissions/combustion-mix is much harder.
And that’s where variable valve timing comes in. Most cars sold to the public have a camshaft designed with a smooth, quiet idle and decent efficiency. But they can improve performance if they open the intake valve early to let in more air. The problem is that if they let in too much air at idle, the RPMs will increase on their own (not safe) or they have to cut ignition which makes for a loud choppy idle. If they use the “mild” cam and adjust it back and forward, they can get the best of both worlds. The VVT is a device (driven by oil pressure or an electronic motor) at the end of the camshaft that can rotate it forward or backward to make this adjustment.
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