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shaft, a dynamic problem also existed. This requiredintensive research into the masses,accelerations,and elasticity characteristics of the tappets,pushrods, rocker arms and springs.

The Polydyne ProfileIn the mid 1950s, with the aid of an electronic

computer, the "Polydyne" formula was employed byIskenderian engineers.This revolutionary camshaftprofile combined the advantage of the polynomialequation with the dynamics of the valve train.In theoperation of high speed, highly flexible systems,interior performance may be attributed to the differ-ence between what the cam commands the valve todo and what the valve actually does. This erraticaction is caused by elasticity, or by the varyingdegree of stiffness or rigidity of the valve train com-ponents. Therefore, the valves do not always followthe dictates of the cam profile under all conditions.

By applying the "Polydyne" formula, it was possi-ble for the first time to design the ca shape to pro-vide the desired valve action. This revolutionary sys-tem of cam design recognizes the fact that flexibilitycannot be reduced or eliminated but, can be com-pensated for. However, with the advances throughthe years in Cylinder Head porting and inductionsystem design, the "Polydyne" Camshafts eventuallyreached their design limitation.

The SLC FormulaAddressing this problem led eventually to the

development by Isky of the SLC* Formula (StrategicLift Command) -- a cam design program which forthe first time made it possible through careful scruti-ny of the profile dynamics to achieve a near "Zero-Jerk" Acceleration Curve! The Result: Valve Controlover a wider RPM Range while capturing greaterarea under the lift curve than ever before!

This Revolutionary new cam design program isso computation and memory intensive, for highest'efficiency it is utilize with Isky's in house state-of-the-art Computer Systems.

Cam profiles designed by Formula SLC are so"Smooth" (higher-revving and easier on critical valvetrain components) many customers report no morebroken rocker arms or bent pushrods as with otherso-called "Computer" Cams they had been run-ning.Top Engine Builders too are amazed to discov-er valve train stability so improved that valve springproblems (breakage, loss of pressure, etc.) are com-pletely eliminated.

The SLC Formula, however, requires one condi-tion to be successfully implemented: A high degreeof manufacturing accuracy and the finest camshaftgrinding equipment, like the Norton Grinder, toobtain the advantages of the mathematically com-puted curve. It is, therefore, obvious that anyattempt to copy these profiles would be impossiblewithout knowledge of the original mathematicalequations.

In conclusion, we would like to point out that ouruse of computer-technology has advanced camshaftdesign to the degree that we can truly state that atIskenderian Racing Cams, "The Cams of the Futureare Here Today!"

Basically, the purpose of a camshaft in an inter-nal combustion engine is to open and close thevalves in correct sequence. In the Otto four-cycleengine, this sequence is timed in relation to thecrankshaft and pistons. The ultimate objective of thecam-shaft function is to "trap" the greatest possibleweight of fuel/air mixture in the cylinders to attain100% volumetric efficiency.

As most everyone knows, nothing starts to moveor stop instantaneously. This property of matter isknown as inertia. If it were not for the inertia of thefuel/air mixture, all engines would be timed to openthe intake valves and to close the exhaust valves atT.D.C. (top dead center), and open exhaust andclose intakes at B.D.C. (bottom dead center), andregard-less of what rpm the engine turned, 100%volumetric efficiency would then be attained.Theaverage "hot rodder," of course, knows that this justdoes not work. He has learned that the exhaustopens before B.D.C. and closes after T.D.C. to takeadvantage of the inertia of the fuel/air mixture, andto provide greater volumetric efficiency as enginespeed increases.

Therefore, a wide variety of camshafts are pro-duced to provide various valve timing combinationsfor different driving applications. The variouscamshaft grinds carry identifying designations suchas: 3/4-race, full race, track grinds, etc. The processof designing, testing, and manufacturing a camshaftis time consuming and costly. To produce a highperformance camshaft, the cam begins as a mathe-matical computation to which manufacturing toler-ances are added. Thus, when a mathematicalexpression, such as a cycloidal cam, is used forhighspeed camshafts, the mathematical computa-tion to which manufacturing tolerances are mathe-matical contour must not vary more than ± .0003inch from the true value at any point.

The foregoing information will now be brought intoa more direct relationship to camshafts. Inertia, whichapplies to gas flow through the induction system, alsoapplies to the camshaft. One instant the valve isseated,the next instant the valve starts to move. As itmoves off the seat, its velocity increases until itreaches its peak; it then gradually slows until itcomes to a stop when fully open.It then enters areverse procedure in the process of closing. Shouldthe engine be accelerated too fast, separation willoccur due to the high frequency inertia forces, andthe valves will no longer follow the dictates of thecamshaft profile. This phenomenon is known as"valve float." To overcome this,high performanceenthusiasts have increased the valve spring pressureto hold the tappet in contact with the cam at alltimes.This worked fairly well, but as spring pressuresincreased it was discovered that the possibility ofwear on the camshaft and tappets was alsoincreased.

Therefore, the two most important functions thatthe cam designer endeavors to achieve are: the ther-modynamic problem of getting the greatest possiblefuel/air mixture charge into the cylinder to drive thepiston;and, the equally important kinematic conditionof keeping the valve train intact at the higher RPMranges at which the engine may operate.

Early camshafts were made with contours whichbelonged to one of two families; the simple polynomi-al or the trigonometric. It was soon discovered thatthe polynomial curves were superior to those of thetrigonometric. They provided smoother action to thevalves, were easier to manufacture, and producedless vibration, wear, stress and noise while requiringless torque to rotate.

The advent of overhead valve engines presentedcertain problems of its own. It was discovered that inaddition to the usual thermodynamic and kinematicproblems present in designing an operational cam-

ADVANCED DESIGN TECHNOLOGY

THEN: Isky created the first Computer Designed“Polydyne Profile” Racing Cams over 30 years ago!NOW: Today’s most advanced designs are computer-generated, using Isky’s exclusive SLC* Formula

*Strategic Lift Command (Patent Pending)

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ISKY ENGINEERING

THE NORTONCAM GRINDER

Rigid quality control in any industry is the secret to success. At ISKY Racing Cams,the Wilson Rockwell Hardness Tester isemployed to insure uniform and correcthardness in every camshaft. Its impor-tance cannot be over emphasized as thesuccess or failure of a racing camshaft istotally dependent upon proper hard-ness.Many cam grinding companies actu-ally "work in the dark" because they donot have this instrumentation and arenever really sure of the hardness factor intheir camshafts. No other camshafts cancompare to those of ISKY, where inspec-tion is an important priority.

VINCO/ADCOLEPRECISIONCAMSHAFTINSPECTION

Over 45 years ago, Ed Iskenderian real-ized that to produce the world's finestracing camshafts required not only thefinest Norton cam grinders,but the finestcamshaft inspection machines as well.Combining the accuracy of the Vincomaster optical dividing head with thetechnological advancement of the Adcoleguarantees accuracy of plus or minusone second of ARC (1/3600 of onedegree). It allows ISKY technicians toinspect a cam profile to within 10 mil-lionths of an inch.

Cam design has come a long way sincethe old days of the simple harmonicdesign. This design determined the camshape by using three separate radii --the nose radius, the flank radius, andthe base circle radius. Today, this simplemethod is considered primitive becauseof the difficulty encountered in accurateinspection, and its poor highspeed per-formance qualities. The simple harmonichas been replaced with a more exactingmethod of plotting the cam contour, the"polar coordinate" method. This methodconsists of computing the shape of thecam in 1/10th-degree angular incre-ments to the fifth decimal point (.00001)or the nearest 10 millionths of an inch.

The number of man-hours required tosolve the countless mathematical equa-tions necessary to produce the polarcoordinate data of the cam contour wasrealized at lskenderian,and as a result,lskenderian pioneered the use of theelectronic computer and the Polydyneformula in racing cam design. The data

obtained from the computer under-goesscrutinous lift, velocity and accelerationcurve study. The lift curve is a graphic chartshowing the actual lifting motion applied tothe tappet by the cam. The velocity curve isthe first differential of the lift curve andshows the change in lift per degree of camrotation. Finally, the acceleration curve isthe first differential of the velocity curve andindicates the change in the rate of changeof lift per degree of cam rotation. It is thisacceleration curve that most demandinglydictates the success of a racing camshaft.

The cam contour, having been properlydetermined, is now ready for transposingfrom the blueprint to the master cam. Themaster cam is a solid piece of Swedish toolsteel,containing the exact lobe configura-tion and angular displacement of the camlobes of the product camshaft and is theheart of the cam grinding machine. It is thismaster that controls the shape of acamshaft as it is ground by the grindingwheel.

DESIGN OF THE MASTER CAM

RESEARCH & DEVELRESEARCH & DEVELOPMENTOPMENT...SPINTRON ENDURANCE TESTING...SPINTRON ENDURANCE TESTING

The demands of Endurance Racing today are such that every manufacturer of critical engine components,(not their customers), should be testing them on a regular basis to guard against the possibility, howeverremote, of catastrophic failure. This point was brought home recently when a well-known east coast valvemanufacturer initiated a massive recall of defective heavy-duty stainless steel valves, after their stemsbegan "snapping off" at the keeper groove. The manufacturer's reputation, already suffering from priorembarassments concerning connecting rod failures,was eroded even further over this unfortunate incident.The lesson to be learned here is that this could have all been avoided had this manufacturer of enginecomponents considered testing to be as important a priority as their advertising campaigns.

We at Isky Racing Cams do recognize the absolute neccesity to regularly test critical engine componentssuch as our Endurance Valve Springs and Roller Lifters. That's why we created the most rigorous real-world endurance test ever established, the grueling Spintron® 1,000 Racing Mile Endurance TestStandard™. The first and only one of its kind in the industry, it's a test with a "Zero" Failure Tolerance,because its either pass or fail for our Racing Valve Springs & Roller Lifters-there is no gray area inbetween! If they don't measure up,we won't sell them-period! We have to,because we know you'redepending on the lskenderian family name to deliver the absolute maximum endurance possible in all ofour valve train components. Your peace of mind and continued customer loyalty are of primary importanceto us and you may rest assured we will never "cut corners" in our efforts to bring you the World's FinestEndurance Racing Valve Springs and Roller Lifters. Our reputation rides with every set!

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