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Rob’s Blog

A question we get asked at HPF nearly every day is what cam should I fit to my engine and is it worth upgrading my heads in my Commodore?

Whether you have a 5.0Lt Holden V8 or a VE with A new 6.0lt L98 V8 there is no doubt a carefully selected head and cam package can give you a significant power increase and excellent bang for your buck. While other cam technologies have taken the spotlight when it comes to making the most power, the old pushrod power plant survives and I believe today more than ever the potential to match the OHV engine’s capabilities “lifter-for-lifter” is within our grasp simply by choosing the correct camshaft and cylinder head package.

There’s way more to camshafts and head design than I could ever explain in just a few paragraphs so I will stick to the main points. The challenge today is that there are tons of heads and cams to choose from in the market place and to choose the right one’s for your application generally involves more thought than simply asking your buddy what cam he runs? With rapidly advancing cylinder head development, cam choice is critical when chasing peak power, reliability and still maintaining some drivability.

The most important aspect of camshaft and head selection is to have a specific application and rpm “goal” in mind before you begin, this needs to be clear along with torque curve, cubic inch displacement and intake manifold design, your camshaft should really be close to the last item on your list and it should be chosen to match all of the other performance pieces on your engine.

Understanding your cylinder head design, type and flow is also critical when selecting your cam and today with EFI technology a properly prepared set of aluminum heads you can run cam’s much bigger than you could 10 years ago, but remember the cam’s only function is to open the valves to move air in and out of the cylinders, if the heads are not capable of moving that air efficiently then running a bigger cam will only hurt power.

With the aid of computer airflow modeling and CNC machining the head porters and manufacturers have been able to increase their potential and take advantage of new cam and valve spring developments. So now a smart engine builder will let his cylinder heads dictate the Lift and duration they run and that is exactly what I recommend you do! Talk too with your head porter or manufacturer and determine the flow characteristics of your heads when selecting your cam specs.

Once you understand the flow characteristics of your heads, the next step is to choose your camshafts lift and duration specification (How high and how long the valve opens). To do this you will need to understand your engine’s expected performance. It’s worth noting that larger displacement engines require more duration than smaller ones because they require more air/fuel mixture to fill their larger displacement cylinders. When choosing lift and duration specifications I focus heavily on the cylinder heads Intake to Exhaust flow percentage. That’s the amount of air the exhaust port can flow vs. the intake port. A head with a higher percentage can use a cam with more closely matched intake and exhaust lobe figures. Conversely, a head with a poor IVE ratio needs more exhaust duration to work well.

Lift refers to how far the valve is opened (or lifted) off its seat. Typically a street performance cam will usually have between .450- and .550-inch lift. More lift can increase power and Increasing the lift without changing duration, increases power without affecting the point of peak power on the rpm band. The rocker arms also have a direct effect on lift because they don’t have a 1:1 lever ratio. A cam that has .318 inch of lobe lift which is how far it lifts the lifter, will open the valve .477 inch with 1.5:1 rocker arms and .508 inch with 1.6:1 rockers so it is important to know what rockers you are using when selecting you cam and I would typically recommend you stick with the stock rocker ratio for most applications. Generally a stock engine will tolerate .500-inch lift before the valves hit the pistons or the valve springs hit coil bind, but any time lift is increased, these clearances should be checked.

Duration is probably the biggest factor in determining an engine’s overall character. When the length of the duration is increased, the engine’s maximum top-end potential will increase as well. This is due to the intake and exhaust valves being held open longer to move more air and fuel through the cylinder. While this long-duration technique is great for making upper-rpm power, there is also a negative effect that must be considered. When the valves stay open longer, it requires them to leave the seat sooner and close back down on it later, which causes an overlap condition. This allows the combusted cylinder pressures inside the cylinders to fall at low rpm, which in turn creates a loss of low-speed torque. As for upper-rpm cylinder-pressure bleeding, there really isn’t enough time for a considerable amount of pressure to disperse before the next engine cycle can begin. It is also worth noting that every degree of 0.050-inch duration is typically worth much more power than 0.010 inch of lift.

The next specification to consider is the correct LSA (Lobe separation angle) if you get that right you might be able to have your cake and eat it too! The LSA represents the number of degrees in crankshaft rotation that separate the intake lobe centerline from the exhaust lobe centerline. A wider LSA figure, i.e. 112-116 degrees, moves the lobe centerlines further apart and will smooth your idle due to the decrease in overlap that creates. The lower the figure, i.e. 106-110 degree, moves the centerlines closer and will increase bottom end torque, but your idle will suffer along with it.

We have carried out a lot of testing on the various engines over the years and we have found that generally the cams with a 108-110 LSA deliver the best torque, however due to their narrow lobe separation idle vacuum is low and idle quality is lost, that’s why for a road car the wider LSA cams (112-114) are generally better as they tend to provide better idle quality and drivability while still delivering a good increase in power and torque. Bottom line here is that it is all about the intended use of the engine and choosing the correct LSA to suit.

Finally one item worth mentioning is valve springs, as they need to be matched to the camshaft and head configuration. Springs today are designed to run with lower pressures and yet still control the valves, this leads to less loading on the valve train and better reliability. It is also worth mentioning that weight at the valve tip can cause problems with springs and valve float so any time you can decrease the weight at the valve tip, you can usually add power. Things like Titanium retainers are a good way to accomplish this.

I know I have only touched on the subject of cam selection but hopefully it gets you thinking about your next project? And let’s face it there’s nothing like the sound of a “camed up” angry V8 to get your juices flowing.. And as always don’t forget you only ever get what you pay for! Always buy good quality components and only use reputable tradesman and workshops to ensure you get the result you’re looking for.
Rob Vickery

More Information:

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HPF Warranty

HPF power packages are warranted for the parts and services installed by HPF. Please contact us for more information.

Additional Notes

  • We recommend all vehicles coming to HPF for tuning run 98 Octane fuel. Please contact us if you have a need to use different fuel.
  • Power figures listed are estimated kilowatts at the flywheel based on results typically obtained by HPF on HPF’s dynos. Typically these are based of a manual vehicle with standard driveline and standard wheels and tyres. Actual power can vary based on each specific vehicle.
  • Modifications such as this package require the vehicle to be in excellent mechanical order.
  • We advise against increasing the power output substantially on high kilometer engines, if your engine has in excessive of 150,000kms please contact us to discuss options.
  • Whilst every attempt is made to ensure prices listed online are correct, they are subject to change at any time.
  • Additional parts may be required in some cases depending on the condition of the vehicle. Cost of these parts and additional labor required may incur additional cost.

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