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Case Study: Intake Lobe Design Constraints on Jan13 2012

by FSD | Print the article |

Arrington Performance

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:

    1. Retard the intake lobe – this will shift the power curve to a higher RPM (This is the opposite of what we want)
    2. Reduce the lift – This may still produce good torque but it will definitely hurt high-speed power
    3. Design the lobe so that we retain the P-to-V, higher lift and shorter duration – This is an obvious choice!
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Any cam designer can design a lobe that will provide more piston-to-valve clearance, more lift and less duration. The advantage that we possess is that we can test the dynamic performance of the valvetrain long before the lobe design information is sent to manufacturing. Most other cam manufacturers must design => manufacture => test using the traditional method of cam design. Many times, the end user is the first test! This dated practice increases costs and takes considerably longer to complete (by orders of magnitude!). By contrast, we can design and test 50-100 lobes in an 8-hour day. We created a baseline 3D model of the Hemi valvetrain using Valvetrain Simulation and correlated our model to measured data taken by Arrington’s Spintron test rig. We modeled the stock spring and a PSI spring that Arrington sells to their customers and began testing the candidate lift curves. We made design changes to the valve lift curves and tested them, one by one in Valvetrain Simulation, until all of our design goals had been achieved. We brought the cams to Arrington Engines where they ran them on their Superflow engine dyno. The first two candidates were both successful in providing increases in both torque and horsepower over the cams they were selling. They immediately placed volume orders for both cam designs.
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How much did all of this design work cost? Absolutely Nothing. 0$, zero, zilch, nada. Since we manufacture the cams for Arrington, we did all the design and analysis work for free. We do not manufacture cams for every engine. We choose to manufacture cams for a select group of engines with which we become intimately familiar. We reverse-engineer and test every component in the valvetrain and use that data as input into our mature 3D Valvetrain Simulation models. Hemi Intake Rocker FEAWe apply nearly 10 years of experience in Valvetrain Simulation for professional race teams which include all three NASCAR series, Grand-AM (also NASCAR sanctioned), American Le-Mans Series, Drag racing and even some customers abroad. We now provide this extremely effective Virtual Prototyping process to our customers. Our distributors will sell these designs to the general public.
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We are currently developing camshaft designs for all of the LS engines (LS1, LS3, LS7, etc.) and the Ford Modular engines (4.6L, 5.4L and 2011+ 5.0L Coyote 32-valve V8). Contact Us for more details.

 


Topic: Featured, Valvetrain Development | Tags: None

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