A: Main stream cam design is accomplished with a polynomial curve fitting program or advanced software that generates curves in segments with differential equations. Design engineers can control profile parameters such as, lobe area, radius of curvature, nose and seat acceleration, seat velocity, as well as, maximum velocity and acceleration, and the degree at which they both occur. When designing these profiles they also consider factors like angular velocity, impact stresses at clearance ramp, camshaft frequency and the natural frequency of the valve spring.
Years of experience, and the Spintron, have defined dynamically acceptable values for these profile parameters, while the profile shape and area is still decided by cut and try on each specific engine. Profiles are now being extensively smoothed until dynamic capabilities are well beyond the maximum RPM of the engine. They have shown that decreasing the maximum values for acceleration, jerk and quirk increases the stability of the valvetrain motion, and in certain cases, has improved power past peak HP RPM.
Designing and generating cam profiles with either of these methods is not a simple task, and requires advanced math knowledge and experience. With only 3% of the world’s population having a math education past the 8th grade, most people would find it too difficult.
Controlled Induction cam profile lift tables are generated from the motion of the piston, and requires only four input variables for each side (opening and closing). They are Seat Duration, Net Cam Lift, Clearance Ramp Height and Rod to Stroke Ratio, which controls the rate of lift curve / area and inversely affects the dynamics. These modified sine waves promote better cylinder filling than the conventional profiles, while meeting all current acceptable dynamic considerations for acceleration and velocity.
You can’t cheat mother nature. The shorter you make the rod to stroke ratio, the more you increase the seat acceleration and maximum velocity, and the sooner maximum velocity is reached in the lift curve. This also creates more time to decelerate to the nose, allowing for a lower nose acceleration. And the inverse is also true.
Using the piston motion math to generate the profile lift tables can only make the seat acceleration and velocity so fast, as 1.1:1 rod to stroke is the minimum allowed in the software. Increasing it only makes the profile softer as it decreases the profile area. So from a 1.1:1 to a 2:1 rod to stroke ratio the profile will always be in the window for acceptable dynamics.!
Q: Would you not need to know the maximum pressure drop in the cylinder relative to the piston position to accurately design a cam for each specific combination?
Q: What do you mean by the "parameter relationships"?
A: We are calculating the required cam values using the relationship between the mean piston velocity and the effective intake charge column, which is determined by the port’s flow capabilities. The total intake port shape affects the direction, velocity and density of the intake charge column from plenum to valve. The port’s mcsa, short turn radius, etc. are all components of the port’s total shape, which together determine the port’s flow capability. So, the minimum cross sectional area of the port has no direct relationship to the mean piston velocity, besides being one of the components of the total port shape, which is directly related.
The minimum cross sectional area of the port has great importance when you are shaping the port to achieve maximum flow and desired flow curve characteristics for the given valve diameter. But it makes no sense to use it mathematically to describe the port to the cylinder. The cylinder does not care how the inlet charge got there.
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A: Potential VE is the possible theoretical gain in cylinder pressure created by an increase in the intake charge velocity, which is specific to the VE%. As the theory goes, once the intake charge column has reached maximum velocity, it can be sustained by the columns inertia and the positive affect from tuning lengths. However, achieving the suggested VE is contingent upon the ports ability to supply the peak piston CFM demand, and having the average port area required to deliver the suggested Volumetric Efficiency at the maximum indicated port velocity.
The intake port should be able to flow the amount of CFM demanded by the piston, when the piston is at it’s maximum velocity (plus lag time). So, at the max piston velocity crank angle, the valve must be at, or above, where the port flows that CFM demand. If the port does not flow the CFM demand, an increase in VE can still be gained, but the amount of gain will depend on the available port flow.
The intake port velocity / intake charge velocity is increased by decreasing the intake valve open time/duration and total lift, while the average port area, from plenum to valve, is increased to accommodate the additional charge volume. How much you can increase the intake port velocity is dictated by the given port design, and the engine performance criteria.
Achieving Potential VE values is not an easy task, and rare to accomplish. So, designing the camshaft and average port area to achieve a gain in cylinder pressure equivalent to the mean intake charge velocity can be accomplished using the Mean Potential VE%.
Every formula for potential VE lacks to mention the cam, while the correct cam duration and lift for achieving the specific port velocity is assumed. Controlled Induction software has combined the camshaft equation with the Potential VE / Piston CFM Demand formulas, and will accurately calculate the required camshaft that will dictate the port velocity that will produce the desired potential VE.
Here is the equation for calculating the Potential VE from Max Velocity (fps):
PotentialVE = (((Val(maxfps / 66.192) ^ 2 / 27.646) + 14.697) / 14.697) * 100
Q: Don't you need to know the low lift flows to be able to design the cam correctly?
QUESTIONS AND ANSWERS
A: No, you would need to know the maximum piston velocity and the crank angle at which it occurred, to accurately design a camshaft. Which is why it is part of the mathematics used in all of our software. Although, the Maximum Piston Velocity is not shown, the crank angle where maximum piston velocity occurs is displayed on the Main Form of the CI7.08 software and all of the CI program's Graph Forms.
A: These are the mathematical relationships between the different parameters. If the parameters are related, changing the value of one will cause a change in the value of the other. Their mathematical relationship describes how much it changes the other parameter, and most of the parameters are related to more than one other parameter. (Examples below)
Bore has a squared relationship to Net Valve Lift
Bore has a squared relationship to Required Intake Valve Area
Stroke has a direct relationship to Required Intake Valve Area
Stroke has a direct relationship to Net Intake Valve Lift
Stroke has a square root relationship to Seat Duration
Port Flow CFM has an inverse, square root relationship to Net Valve Lift
VE% has a direct relationship to Net Intake Valve Lift
Mean Port Velocity has an inverse, square root relationship to Seat Duration
Mean Port Velocity has an inverse, square root relationship to Net Intake Valve Lift
Mean Piston Velocity has a square root relationship to Seat Duration
Mean Piston Velocity has a direct relationship to Net Intake Valve Lift
Q: What makes your profiles so different?
Q: Could you explain Potential VE?
Camshaft Design & Profile Generation Software
Q: Why don’t you use minimum cross sectional area?
ENGINE MODELING & CAMSHAFT DESIGN SOFTWARE
( Jones Cam Design Equation )
A: The camshaft conducts the orchestration of the internal combustion engine. And there is not a single instrument, nor any one point in the piece, that can define the arrangement. In order to fill the demand for the cylinder’s rate of change in volume, through a given RPM range, requires an adequate intake track flow curve with the right valve opening curve. Every point in the intake track is affected by all points before it and will affect all the points after it. Smoothly accelerating the entire inlet charge column with the valve curtain area pressure differential will increase the volumetric efficiency, and inertial ram energy.
The port flow at every point of lift has an affect on cylinder filling. But the camshaft profiles are not shaped by the port flow values at each of those points. The Intake Seat Duration is determined by the relationship between the Mean Piston Velocity FPM and Mean Port Velocity in FPM, at Peak HP RPM. The Intake Net Valve Lift is dictated by the effective valve area calculated from the given intake port flow CFM at the convergence valve lift, and it's relationship to the cylinder's calculated value for the required valve area. The rate of the valve lift curve is determined by the Piston Velocity Curve, which is dictated by the Rod to Stroke Ratio. So you have an opening curve with the appropriate time/duration, required valve lift and a Valve Opening Lift Curve that mirrors the Piston motion. What would you like to change, because you increased, or decreased the port flow 10 CFM at .200" valve lift? And what would you expect to gain?