Why Do I Want An Aftermarket Cam

The internal combustion engine has been under developement for well over 100 years, and will be for decades to come.
The examples that we see come to the market as a car, truck, boat, motorcycle, or any other application, are the designs of one group of people, and to some extent will be a compromise.

Taking thier product and tayloring to better suit your needs is the prodominant reason to look to an aftermarket camshaft.

I have deliberately avoided the term 'performance' cam, as it seems synonimous with, more power, more revs, worse drivability, and less fuel economy. 
It is equally posible that the 'performance' you want is better fuel economy or more bottom-end power, and top-end power may be irrelevant.

There are many reasons why a factory cam may not be ideal for you. It may be an older vehicle that could benifit from a more modern design, with a wider operating rpm range. Or it could be that the vehicle that has served you well and you enjoy driving it, but could just do with a bit more power as a more economical solution than changing vehicles.

Sometimes manufacturers are in competition with a rival to make the most power. This can lead to vehicles that make all thier power at the top-end. Makes for some good numbers for the marketing team, but in reality a stronger mid-range will feel faster. When you pull out to pass are you doing 6000 rpm, or 3000 or less? The small block Chevy 350HP cam is a good example of this. Yes it made good power in it's day, but the power is all at higher revs and by todays standard it is an old lazy design. Today a cam can produce that same top end power with a far better mid-range, making for a vehicle that is nicer to drive and is faster.

The most popular style of cam we do for V8 cars has a resonable lump to the idle, because V8s sound great and the world should know you have one even if you are parked at the lights, has very strong mid-range because that is where you are usually trying to accellerate the vehicle, but does not run to high rpm. The two main resons people stay away from high rpm is that an engine taylored to the higher rpm will have less bottom end power, which makes for a car that is not as nice to drive and doesn't accellerate as well from low speed, and higher rpm engines need better quality and therefore more expensive internal parts.

Engine transplants, or retro-fits, will often benifit from a camshaft change. An engine designed for a passenger car is unlikely to be cammed idealy for your street rod, boat, or offroad vehicle.

Turbo charging and super charging also radically change the camshaft requirements of an engine, and the exact specs of the turbo or super charger as well as the type of power you want will change what cam design is required.

More modern vehicles can also benefit. When a devoloper has met thier design criteria they are unlikely to continue spending money making it better, or they may develope the 'top of the line' model and then detune it and sell it as a more basic model. This often leaves room for later improvement.

Or maybe you do want the race cam. Lots of power, lots of revs, and the BIG idle sound.

What ever your needs, Kennelly can tailor a package to suit. Contact us today to see how we can help you achieve what you want.   

Selecting A Camshaft

This section is written to give you some idea of how the other modifications to your engine, and the intended use of the engine, will effect the selection of a cam profile. At Kennelly Cams we recommend you contact us to discuss your specific requirements.

Some of the main factors effecting camshaft selection are:

Engine RPM

This is arguable the most important consideration in choosing a camshaft.
What idle quality do you expect and how do you want it to sound?
What drivability do you expect at low RPM?
How important is the mid-range power, and how aggressively do you want the power to come on?
How far do you want the engine to rev out?

In brief, a shorter duration will suit lower rpm, and longer duration will suit higher.
Tighter lobe center angles (LCA) will promote strong mid-range power, but at the expense of idle quality and it will also limit how far the engine revs. Wider LCA will reduce over-lap improving idle quality and will allow the engine to rev out further, but at the expense of mid-range punch.
Tighter centers give a shorter power band with lots of mid-range punch, wider centers give a wider smoother power band.

High rpm engine suffer considerably more from friction loses. During the exhaust stroke, pumping pressure and friction can be reduced by opening the exhaust valve earlier. This means wider LCA and more duration. Opening the exhaust valve earlier will reduce the power produced by the gas pressure pushing against the piston, but this will more than be made up for with the reduction of parasitic friction and pumping loses.

Engine Size

Bigger cylinder capacity typically needs more duration and wider center lines to produce similar engine characteristics to a smaller engine. For example a 5 litre engine with stock internals, that you want to have a reasonable lump to the idle but run on a stock torque converter might run 218 degrees at .050" on 108 lobe center angle (LCA). A 7 litre engine with stock internals, with the same idle qualities and also running a stock torque converter, might run 230 degrees at .050" on 110 lobe center angle.

Compression Ratio

It is worth considering the compression ratio when choosing a cam. One of the first modification that a cam manufacturer might recommend is a 1 point increase in the compression ratio. This helps improve the crispness or throttle response at low rpm. That means you can get away with a bit more cam and get more mid-range power.
If you want an engine that drives nicely at low rpm and you only have 8.5 or 9:1 compression, you will need to stay mild in the cam. Increasing to 9.5 or 10:1 compression will let you run an extra 6 to 10 degrees more duration while still maintaining bottom end power.
Very low compression engines as found in older engines, like shorter duration and tighter LCA

Intake System

There are many variations of intake that will effect cam choice. Single or dual plane, carb or injected, individual runner?

Factory fuel injection on many engines can be very sensitive to cam changes. On these systems, if you really want to change cam, avoid too much overlap. Overlap will cause pulsing in the intake system that injection systems often cannot interpret.
However some other systems, usually with mass airflow sensors, can sense the change in the volume of air going into the engine at different rpm, and adjust fuel flow to suit the changed cylinder efficiency.

Single and dual plane manifolds can come in many different shapes and sizes and performance will change with each.
Probably the most important thing is that a dual plane manifold, whilst producing good bottom-end power, will not let the engine rev. There is no point running a dual plane manifold and then trying to cam it to get good high rpm power. All that would be doing is running a manifold that hurts the top end, and a cam that hurts the bottom. Net result, no strong power anywhere.

Individual runner carburetors or injection are the ultimate. This prevents intake pulses mixing between the cylinders, thus allowing very strong pressure wave supercharging of the cylinders. Because individual cylinders are not being effected by pressure waves from other cylinder, more cam duration can be used without unduly effecting the smoothness of the bottom-end power. Typically 10 degrees more.

Port Flow

The most important thing about the cylinder head flow might seem quite obvious but is often overlooked; is there enough?
If you do not have enough intake flow for the amount of horsepower you want to make you will need to leave the valve open longer to try to fill the cylinder. This extra duration will hurt bottom-end and mid-range power leaving a very compromised power curve. If at all possible fix the flow problem.  As a rule of thumb, 100cfm measured at 28 in/h2o is good for about 28HP per cylinder.

The most important area to look at on exhaust flow is; how much flow does the exhaust have compared to the intake at 35% of full lift. When the exhaust valve first opens the burnt gas in the cylinder is at high pressure, and a good flowing valve will empty the cylinder quickly. So if you have good flow at this point, you can open the exhaust valve a little later yet still relieve enough gas that pumping pressure on the exhaust stroke will not cost too much power. The later exhaust opening means the exhaust gas pressure on the piston is kept high a little longer making more power.
An exhaust to intake ratio of 80% (at 35% lift) is fairly normal for a 2 valve engine, and would typically require 4-10 degrees more exhaust duration than inlet, depending on the engine size. A 4 valve engine can often achieve 110% (10% more exhaust flow than intake) or more, and can usually get away with less exhaust duration than intake. 

Supercharged / Turbo Charged

Supercharged engines typically have a shorter intake, longer exhaust, and wider lobe center angle (LCA).
Supercharged engines can continue pushing charge into the cylinder longer than an NA (normally asperated) engine, and also the greater pressure differential between the manifold and the cylinder means the cylinder is filled quicker. This means they like a shorter intake duration on a later centerline, compared to thier NA counterparts.
Higher cylinder pressure after combustion means more gas to get rid of, so the exhaust valve is opened earlier than on an NA engine. This means longer exhaust duration, on an earlier centerline.
Early exhaust centerline and late intake centerline means a wider LCA. This means there is less overlap which also helps stop the pressurized intake charge being lost out the exhaust valve.

Turbo Charged engines are more complicated.
Before the turbo charger reaches an efficient speed the engine behaves much like an NA engine, albeit a low compression one. This means to get the cylinder filled efficiently and producing good amounts of exhaust gas to 'spool up' the turbo the ideal would be a relatively tight LCA. However once the turbo has 'spooled up' and is efficient the engine behaves more like a conventional supercharged engine and wants a wider LCA.
Turbo engine camshaft selection, and the overall performance of the engine, is greatly effected by the turbo selection.
It is easier to get a turbo to spool up at lower rpm by choosing a smaller exhaust turbine housing than by manipulating cams. This means the cams can then be optimised for 'on boost' performance.
Typically higher boost levels, and higher rpm, require more cam duration. The main difference between supercharged and turbo charged engines, is that turbo engines do not flow from the intake out the exhaust, at overlap, as easily as a supercharged engine, and therefore tend to open the intake valve earlier. So turbo engines tend to have a longer duration intake than a supercharged engine, but still shorter than an NA engine.
The turbo charger should be selected before the camshaft, remembering that a turbo, much like a supercharger, can restrict power if it is not big enough.

Do's and Don'ts For Fitting And Running In Camshafts.

As a critical engine component, camshafts should always be fitted in accordance with good engine building practices.

The camshaft is one component in a system and it must be checked that the camshaft is compatible with all other components including but not limited to: valve springs, lifters and push-rods.

Check for adequate clearance between all parts of the valve train and, any fixed part of the engine as well as all other components in the valve train.

New and re-profiled camshafts, in particular flat tappet style cams, should always be fitted with new or re-profiled lifters.

Mechanical tappets should be set as accurate as possible before starting the engine and bring up to temperature.

Hydraulic lifters should be bled down before assembly into the engine. These may well be noisy on start up but should quieten down within a few minutes. Pumped up hydraulic lifters will cause the valves to be held open, preventing the engine from starting.

The tight radius of the cam lobe nose has the smallest contact area of any part of the cam lobe and is most susceptible to damage during run in (break in). This area is highest loaded at low speed. To ensure the lobe and it's follower successfully run in, and to achieve maximum life span of the components, a few basic precautions must be taken.

Engines with high valve spring pressures will require lighter valve springs fitting for running in. With dual springs this can often be accomplished by temporarily removing the inner spring.

Cam lobes on non roller type camshafts should be lubricated with a quality moly (molybdenum disulphide) based lube that will adhere to the lobe until, and during, start up. The lifter face or rocker that runs against the cam lobe should also be liberally coated with lube.

The engine should be fitted with a new oil filter and filled with new oil. Note that not all oils are suitable for the running in procedure. Kennelly Cams recommend using mineral oil for the running in of flat tappet and slipper type rocker engines, and if you do not know that the oil has a high zinc (ZDDP) content, Kennelly Cams recommend using an appropriate zinc additive.

Oil and fuel systems should be primed, and ignition timing set statically before cranking the engine. Engine cranking time should be kept to a minimum, and slow speed operation must be avoided for the first 30 minutes of running. The engine should be immediately brought up to 2000 rpm upon start up and not idled for the first 30 minutes.

Flat tappet cams in most applications are designed to cause the lifter to rotate. This rotation converts what would have been a sliding motion into a rolling motion without reducing oil entrainment velocity and is essential in avoiding excessive wear. Where practical Kennelly Cams recommend running a flat tappet engine with the lifters or push-rods visible to observe that rotation is taking place. This can often be achieved by briefly running the engine with the rocker cover(s) or side plate removed, or a modified part fitted in place that allows visibility while still containing (most of) the oil.

The engine revs may be varied over 2000 rpm, e.g. between 2000 and 3000, to vary the load on the rings and other components that may also be running in at the same time. 

During this time the engine should be checked for fluid leaks and the temperature closely monitored. Also listen for any unusual noises. It is safe to shut the engine down at any stage, but upon restart the engine must be returned to 2000+ rpm until it has done a total of 30 minutes running.

The idle speed may now be set at the normal rpm, and tappet settings or lash should be checked.

The engine should not be run over 60% of the normal redline until the correct valve springs have been fitted, and the oil and oil filter changed. Kennelly Cams recommend this is done before 500km is traveled.

What Your Camshaft Needs From Your Engine's Oil.

In engines that do not use a roller cam follower, it is the job of the oil to minimise destructive friction between the cam lobe and what ever cam follower the valve train uses.

This job is done in 3 phases.

Firstly the oil should maintain a film between the lobe and follower. Second it should encourage oil to stay between the lobe and follower after the film has broken down. Lastly it should provide a residual friction reducing barrier when no oil is left between the lobe and follower.

The ability of the oil to maintain a film between the two parts under increasing load is measured as Film Shear Strength. This is often confused with viscosity but in reality is a product of many factors including oil type, quality and additives used.

As the oil film starts to break down under increasing load, the ability to maintain an oil presence between the parts is measured as Hydrodynamic Lubricity. Different base oils will have a different amount of inherent hydrodynamic lubricity. Mineral base oils and ester based synthetic oils have better hydrodynamic lubricity than group 4 synthetic base oils. It is often improved with an additive such as ZDDP (Zinc Dialkyldithiophosphate).

The task of reducing friction when no oil is left between the parts is left to friction modifiers that have bonded to the surfaces. Molybdenum Disulphide (Moly) is one common additive used for this. Molybdenum Disulphide has an affinity for ferrous metals, and will bond to the surface of both the camshaft and lifters, remaining after the oil has been forced out. Friction modifiers provide a limited amount of protection against damaging wear when metal to metal contact occurs. The valve train design, including valve spring pressure, must be such that metal to metal contact only occurs for very short periods if the lobe and follower are to have a long and happy life.

Kennelly recommend using a Moly based paste, such as Rocol ASP, to lubricate the cam lobes during assemble, and running a ZDDP, or ZDDP and Moly, additive in your engine oil during the running in period...for the sake of your new cam.

What Are Entrainment Velocity And Hydrodynamic Lubricity.

In engines that do not use a roller cam follower, oil entrainment velocity is created across the contact face, between the cam lobe and the cam follower. It is the speed, or velocity, that the contact point of the two parts is moving across surfaces of the two parts.

As the two surface move there are two distinctly different motions that can create entrainment velocity and the total entrainment velocity can be considered the sum of the velocity created by the two different motions.

The Hydrodynamic Lubricity of an oil is its willingness to travel between two parts, from a higher pressure zone on one side to a lower pressure zone on the other.

Wiping Motion
Wiping is probably the most obvious motion. We can use the example of when the cam lobe to follower contact is on the cam base circle. Although with a mechanical cam there is no forced contact at this point it is the easiest to explain.

During this motion the contact point stays at the same place on the follower and the cam lobe wipes or slide past this point. Friction is created at this point, and the higher the load and the smaller the contact patch the higher the friction.

The oil surrounding the contact area develops a high pressure zone on the side where it is being drawn towards the contact point, and a low pressure zone on the side where the two parts are separating after contact. The ability of the oil to travel between the two parts, from the high pressure side to the low pressure side, is the oils hydrodynamic lubricity.

Rolling Motion
During cam lift the contact patch between the cam lobe and follower is most often moving across the face of the cam follower. If the contact patch is moving across the face of the follower at the same velocity that the surface of the cam lobe is rotating at, then the motion is the same as that of a roller, with no sliding friction created at the contact point. On the side of the contact patch which the parts are rolling towards a high pressure zone forms in the surrounding oil, and on the side the parts are rolling away from a low pressure zone exists. Again a good oil will travel between the two parts driven by the difference in pressure on either side.

Troublesome Cancellations
At some stage during cam lift all non-roller valve trains will have wiping motion and rolling motion entrainment velocities that cancel each other out. That means no high and low pressure zones to encourage oil to get between the cam and follower.

If this happens at a time when the load on the parts is sufficiently high, and the contact area is sufficiently low, the oil film will break down and have a problem. There is still friction caused by the wiping motion, but there is no reason for the oil get between the two parts to where the friction is.

Hopefully friction modifiers in the oil will have left some deposits on the surface of the parts which will give some protection during this time, but in any case these periods of low or zero entrainment velocity must be kept short in duration so lubrication can be resumed before catastrophic damage is done.

Is Entrainment Velocity Likely A Problem In My Engine
Flat tappet push-rod and bucket style OHC valve trains do not typically have big problems with this, but if you are getting lobe wear that is worse either side of the lobe nose causing flats that give the nose a pointed triangle shape it may need looking in to.

Rocker style OHC engines on the other hand it needs careful consideration. Because the rocker has a curved surface rather than a flat surface for the lobe to run against, contact patch is reduced and the oil film is more likely to break down. Further more because of the asymmetric motion, rockers which have the cam rotating towards the valve end are likely to see longer periods of low entrainment velocity.

Pinto engines have the oil spray bar on the intake side to counter this, SR Nissan engines are hard on intake cams when the oiling becomes marginal, and OHC motorcycles typically wear the exhaust rocker worst for the same reason.

Keep good oil in your engine and use well designed cams and they will live long and prosper.