The VVT actually is at full advance at idle, no valve overlap. At around 1500 RPM it goes to around 12 degrees, which is normal run mode. At 3000-3500 RPM the VVT goes into full retard, which is around 25 degrees. When driving a Trailblazer/Envoy you can definitely feel the difference when it goes into full retard. It's almost like the secondaries on a 4 barrel opening up.
As far as locking the phasers out, somewhere in the middle would be my best guess. On the other hand, why would you want to? I've never heard of any 4200's having problems. These engines have a good torque curve from 1500 all the way to 4000 RPM
I know the 3V Ford engines have had cam phaser lock outs and limiters for years. It has mostly to do with the reliability of the design.
The intake ports on the 4200 flow over 300 CFM, I'm guessing the 2V Jag falls short in that regard.
Marc, AKA, EFI-DIY, has done a bunch of playing around with the VVT setup on these engines, I know he had custom cams made and locked his out at one time. He still pops in every once in awhile at the Inliners forum.
