DO YOU SWEAR TO TELL THE TRUTH
There are plenty of cam experts to tell you what cam you need...as long as you are buying the cam from them. None of these experts can, or will, tell you how to select the right cam. There has never been a "How to Select the Right Cam” article that has ever explained how to select the right cam. Although, many of these articles tell you that the right cam cannot be determined with a mathematical formula or equation. But almost every one of these articles tells you that the cam requirement of an engine is related to, and affected by engine parameters such as, the bore, stroke, valve area, port area and port flow CFM… and it is.
There is just one problem with their misinformation. Any engine parameter that affects the requirement of the camshaft has a relationship with the camshaft that can be written in a mathematical formula, or equation. When you combine the mathematical formulas for each of the related parameters, you've got a cam requirement equation. So, to help their confusion, we are going to write out all the formulas and equations that describe these relationships and calculate the cam requirement.
Below you will find a portion of our mathematics that has been in use and proving itself for decades. Broken down into several formulas, this will determine the Camshaft's Intake Seat Duration and Net Valve Lift. If you are not smart enough to understand how and why this math works, you have about a 1 in a million chance of being a successful race engine builder.
VE = Volumetric Efficiency %
PI = 3.141592654
B = Bore in inches
PDA = Piston Disc Area = (B^2 * PI / 4)
S = Stroke in inches
CD = CylDisp = PDA * S
R = Rod Center distance in inches
N = Number of Cylinders
VAR = Valve Area Required = CD * HPRPM / 108,000 ( 108,000 = 3456 * (125 / 4) ) a 1 sq.in. unrestricted orifice flows 125 cfm @ 20.54 in/h2o or 300 fps
HPRPM = RPM at Peak HP
HPFPM = Mean Piston Velocity at Peak HP RPM
IVD = Intake Valve Diameter
IVSTD = Intake Valve Stem Diameter
IVA = Intake Valve Area = (IVD^2*(PI/4)) - (IVSTD^2 * (PI/4))
ICFM = Intake Port Flow CFM @ convergence valve lift
In/H2o = Bench Test Pressure
FPS = Mean Port Velocity
EVA = Effective Valve Area = ((ICFM / SQRT(In/H2o)) / 27.58)
EVD = Effective Valve Diameter = SQRT(EVA * 4 / PI)
EVC = Effective Valve Circumference = EVD * PI
ReqILift = (VAR * (300 / FPS)) / EVC
ISeat = Intake Seat Duration = SQRT((HPFPM / (FPS * 60)) * PI) * 360
NOTE: You can’t compare these seat duration values to a conventionally designed profile’s seat duration. Our modified sin wave designed profiles will have 4 to 14 more degrees at seat, with the same duration @ .050”, depending on the rod to stroke ratio. Cam profiles should be compared at .050” and .100” duration. Below is the math routine to generate our profiles.
CAM PROFILE GENERATION – ONE SIDE FROM TOP OF LOBE DOWN
R2S = Rod to Stroke = R / S
theta = 0
deg = 0
idura = iseatdura + 4 ---- add 4 so we can cut off 2 from each side to mate in the clearance ramp
deg = 0
theta = PI ----TOP OF IS BOTTOM OF STROKE
Do Until deg >= idura / 2
vel2 = vel1
cam1 = (((r2s + 0.5 * 1 - ((1 / 2) * Cos(theta) + r2s) * Sqr(1 - ((1 / (2 * r2s)) * Sin(theta)) ^ 2) / 1) * (reqilift / irock)) + icamlash
rad = Sqr((r2s) ^ 2 - 0.25 * (Sin(theta)) ^ 2)
vel1 = Abs(0.5 * Sin(theta) * (1 + 0.5 * Cos(theta) / rad) * (2) * (PI / 180) * (360 / (idura)) * (reqilift / irock))
theta = theta + (((PI / 180) * (360 / idura)) / 4)
deg = deg + 0.25
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SOMETHING TO THINK ABOUT
The camshaft conducts the orchestration of the internal combustion engine. And there is not a single parameter 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. The smoother we can accelerate the entire inlet charge column with the valve curtain area pressure differential, the greater volumetric efficiency and inertial ram energy we can expect.
CONTROLLED INDUCTION 2020
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Camshaft Design & Profile Generation Software
ENGINE MODELING & CAMSHAFT DESIGN SOFTWARE
Controlled Induction 2020 is our latest, most versatile and accurate cam design software. It combines, replaces and succeeds all of our previous software. Beyond calculating your given engine's cam design requirements, this software will generate, and save to file, the cam profile lift tables. These files can be used in Engine Analyzer Pro and Dynomation software to simulate, and verify, each cam design's performance. You can also have Howards Cams CNC grind these profiles on the cam core of your choice, using these same lift table files.
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