Eventually this trickled down to GM's incorporation of this technology into the Gen IV 6.2L L92 Escalade motor for the 2007 model year. GM's design placed a cam phaser on the face of the cam, which takes the place of a fixed timing set that would either speed up or delay the cam timing (instead of being directly proportional to the crank) by utilizing oil pressure. The design was such that the phaser could easily be replaced by a fixed timing set like any other Gen IV, but in utilizing the phaser (via some modification,) COMP Cams has managed to harness the awesome potential of this technology with a line of camshaft kits that add lift and duration without causing piston-to-valve clearance issues. In a recent trip down to COMP's R&D facilities in Memphis, TN we were able to experience a taste of the awesome potential of these new VVT cams, seeing just how they faired on the SuperFlow 902 engine dyno using a stock L92 motor.
For years the imports, and...
For years the imports, and even the blue oval boys, have been using variable valve timing (VVT) technology to experience increased power gains throughout a broader rpm range. Though more common with overhead cam engines, in 1991 Clemson University came up with a design that would also allow pushrod engines to utilize optimized cam timing.
As you can see, the design...
As you can see, the design of the variable valve timing cam is radically different than your standard Gen III (or even Gen IV)...
...The holes through the barrel...
...The holes through the barrel of the cam channel pressurized oil, feeding the phaser, which bolts to the face of the cam instead of a fixed timing sprocket.
The bolt that holds the phaser...
The bolt that holds the phaser to the cam is actually a valve, which feeds a number of holes in the phaser. Pulse width modulation controls how much oil pressure is fed into the phaser, which in turn makes the cam timing retard. When there is no pressure it is locked to full advance.
First we base-lined the stock...
First we base-lined the stock GM L92 motor using the factory computer and Dynatech long tube headers. The healthy 376-cube motor made 430.3 hp and 434.7 lb-ft on the SuperFlow engine dyno.
COMP Cams Research and Development...
COMP Cams Research and Development Dyno Operator Rich Smith started breaking down the L92 for the cam transplant and phaser modification by removing the crank pulley...
...and water pump.
The timing cover comes off...
The timing cover comes off next-note the difference in shape from your Gen III cover and the electronics that control the phaser.
The bolt, that as previously...
The bolt, that as previously mentioned is actually a valve, is controlled by an electromagnet. GM technically calls it a "Camshaft Positioning Actuator Magnet." The back of the electromagnet and connector can be seen when looking at the timing cover externally. On the inside of the timing chain cover is a small pin that is controlled by the electromagnet, which has a range of motion of approximately .250-inch. This pin is what physically pushes on the cam phaser valve/bolt to control the oil pressure being fed in and out of the phaser. The electromagnet is controlled by the PCM.