The cam that you run in a motor depends on what the motor is powering. It is pointless to fit a cam that will increase the torque at 5000 rpm, if you have an auto that will spend most of its driving at 2000 to 3000 rpms. It really has to suit the overall gear ratio that the car has.
To obtain better filling at higher rpms, you have to use a cam with a longer duration, and the inlet lobe center will have to be retarded to move the torque peak, higher up the range. This will move the torque away from the low end rpms, to increase the top end. This type of output would not suit an auto, but would suit a 5/6 speed manual that can use the gears to keep the engine operating in the 3000 to 6000 rpm range, because it would be a 'dog' below 3000 rpms.
So the choice is;
If you are keeping the auto and the 3.5/3.7 final drive ratio, you need to keep the timing the way it is, and increase the torque by increasing the lift.
If you are keeping the auto but using a lower 4.1/4.4 final drive ratio, you could increase the lift and increase the duration, slightly.
If you are using a 5/6 speed manual, the low rpm torque is not important, as you can use the gears to stay in the higher rpms. This engine could use longer duration higher lift cams, with the lobe center retarded to move the torque peak further up the rpm range.
As for forced induction, I don't think anybody will be using enought boost to need the exhaust timing advanced or extended. But if this should be the case, advancing the exhaust lobe center will allow the cylinder to drop the higher pressure, before the up stroke.
Increasing the overlap, by holding the exhaust open so that the inlet flow will cool the exhaust valve, is used when the boost is high and held for an extended peroid. By the time you get to this stage, you would need sodium filled exhaust valves and a lot of other changes.
Harvey.
