Variable Valve Timing (VVT) is a system that automatically adjusts Valve Timing.
**The table below shows the engines that were originally equipped with VVT.**
| Displacement | RPO Code | |||||
| 4.8L | L20 | |||||
| 5.3L | LC9 | LH9 | LMF | LMG | ||
| 6.0L | L76 | L96 | LC8 | LFA | LY6 | LZ1 |
| 6.2L | L92 | L94 | L99 | L9H | ||
How is it identified?
Engines with VVT will have a camshaft phaser actuator on the timing cover. They also have a 5-pin connector for the VVT and camshaft sensor.
Engines without VVT will not have the actuator. They only have a 3-pin connector for the camshaft sensor.
GM used 2 different camshaft phasers.
| Camshaft Phaser Actuator P/N | Years Used | Degrees of Rotation |
| 12585994 | 2007-08 | 62 degrees |
| 12606358 | 2008-15 | 52 degrees |
How does it work?
The computer senses engine load. It also monitors valve timing through the camshaft position sensor. It uses these inputs to determine the best valve timing for the current conditions.
The computer sends a signal to a solenoid on the timing cover. The solenoid controls oil flow through a special control valve in the camshaft bolt. The valve sends oil into the phaser control chambers.
The actuator rotates one way or the other, depending on the oil flow. That rotation is used to Advance or Retard the Camshaft as needed.
How does it affect performance?
VVT gives you the best of both worlds. It can advance valve timing for a smooth idle and low-end torque. It can also retard the valve timing for more top-end power. And, it is all done automatically!
VVT becomes an issue when swapping a cam:
- Piston to Valve Clearance can be a problem.
- Your choices for Valve Lift and Duration are limited.
- Valve Spring Pressure is also limited.