We worked with Arrington Performance in Martinsville, VA. and began designing and manufacturing a new line of camshafts for the 6.1 Liter Dodge Hemi engines. Their goals were simple. They wanted the new cams to make more Power and more Torque but they still wanted the new cams to work with the valve reliefs in the stock pistons. They wanted their customers to be able to perform the cam swap without removing the engine and replacing or modifying the pistons. Their best selling cam at that time was at the very limit of piston-to-valve clearance for the intake valve. That meant that we had to design the new cams with the existing piston-to-valve clearance as a limit that could not be exceeded. We used Engine Simulation to explore the design space for cam specs that would produce the gains in power and torque that we desired. In order to make more torque, we needed to shorten the duration of the intake valve lift curve (slightly). However, we also needed to make more power. Shortening the intake duration would have an opposite effect on high speed power. We needed a new valve lift curve with equal or greater area when compared to the old design so we increased peak valve lift by .020″ (.5mm) and shortened the duration by a mere 2º. Such a significant increase in lift and a minimal change in duration would undoubtedly exceed our hard limit for piston-to-valve clearance by which we are constrained. Now we’ve really boxed ourselves into a corner because as any cam designer knows, when you decrease duration and increase lift it becomes more challenging to keep the valvetrain under control at high RPM. Consider this analogy: Imagine you are holding a stack of 5 plates in your hands. What would happen if you raised them up and back down over a distance of 1 foot and a time period of 10 seconds? There is no spring keeping the plates in contact with one another, only gravity. Not much would happen – they would all remain in contact with one another. Now what would happen if you raised and lowered the stack of plates 1.5 feet over 1 second’s time? You’d have a mess of broken plates on the floor. That’s quite an exaggerated comparison but you get the idea. When you increase lift and shorten the duration of the event it becomes increasingly difficult to keep the valvetrain components working together in harmony as RPM increases (decreasing time interval). Let’s not forget that since we’ve increased the lift, we now have less piston-to-valve clearance. We cannot exceed our P-to-V constraint so we have to make a change. We have 3 choices:
- Retard the intake lobe – this will shift the power curve to a higher RPM (This is the opposite of what we want)
- Reduce the lift – This may still produce good torque but it will definitely hurt high-speed power
- Design the lobe so that we retain the P-to-V, higher lift and shorter duration – This is an obvious choice!