When you consider valve-timing events, you also have to consider all the other elements acting on the fuel charge and combustion gases in the cylinders. An earlier-closing intake valve starts building cylinder pressure sooner. This increases low-speed torque due to greater cylinder pressures, but it means that the engine is having to work harder to compress the charge. As previously explained, a later-closing intake can enhance top-end torque at the expense of low-end torque, but you can get most of the torque back on the low end with an increased compression ratio. What you look for is a cam profile that promotes increased cylinder filling with earlier intake opening so that the valve is farther off the seat during the early portion of the intake stroke. Then you want to delay the exhaust-valve opening as much as possible to take advantage of all the energy you can from the combustion process before you blow down the cylinder. A quick-opening exhaust valve is helpful here, but, again, there are trade-offs.

This combination builds good torque but tends to increase valve overlap at TDC. This is where the cam lobe separation angle takes control. The lobe separation angle is the angle between the peak of the intake lobe and the peak of the exhaust lobe expressed in cam degrees. Tighter lobe separation angles (less than 110 degrees) make more torque and horsepower, but, with more overlap, the engine experiences poor idle quality and high fuel consumption. Opening up the lobe separation angles (more than 110 degrees) broadens the power band while improving idle and part throttle characteristics. With these wider lobe separation angles, peak torque and power are generally reduced, but the engine becomes very smooth and drivable.

-By John Baechtel