The choice of a camera can cause anyone a headache , especially when they select the wrong model for the job. There’s an abundance of science when choosing a cam be sure to read on and we’ll assist you in navigating through the finer points.
The camshaft is other than a steel or cast iron shaft, with a set of lobes that are strategically located across the length. Each lobe is able to open and close an air valve by moving an actuator, pushrod or a rocker arm. Or in the case of an overhead cam motor, by the movement of a cam follower or directly valve action.
The dimensions, shape and location of the camshaft’s lobes determines the valve’s timing as well as the engine’s compression and breathing characteristics. This will determine the potential performance of the engine and the rpm range in which it will produce the most torque and power.
The selection of to select the “right” camshaft then it is not just the primary element of building an engine with performance, but its central point. The cam is the engine’s foundation and is the primary factor that determines the other components to be used to construct your engine (cylinder heads pistons, valvetrains inlet and exhaust pipes as well as carburetors).
The majority of camshaft manufacturers provide an array of off-the-shelf grindings that are specifically designed for particular applications. The trick to choosing the cam that can provide the performance you desire is to identify the rpm range at which the engine will produce the greatest power, then select one that is compatible with the characteristics of breathing in the head of the cylinder, inlet and exhaust manifolds, the weight and the gearing of the vehicle that the engine will be running in.
If you’re building a massive stroker motor to be used in an ProStock drag car, with an aftermarket 500-600 cubic inch block, and piston heads that have ports of the size of a fist that can flow more than 500 cfm with .900″ the valve height, this engine will require a huge cam that has a lot of duration, valve lift, and overlap.
However If you’re building a tiny block engine for street use intended to be a daily driver that has the option of an automated transmission as well as standard gearing, you’ll need a cam that offers decent drivability and plenty of mid- to low-range acceleration and throttle responsive. It is also recommended to select the cylinder heads with tiny intake runner volumes to ensure high air velocity and good throttle response in the low to mid-range speeds and a split-plenum 180-degree high-rise intake manifold, and a properly-sized carburetor.
Don’t overdo your work
The biggest error that engines builders commit is overcame an engine. Utilizing a cam with too much lift in the valve or duration as well as too much overlap between valves to the purpose could result in negative effects.
Everyone likes big numbers however, if the specifications for your cam aren’t in line with the engine you’re building , or the specific application it’s going to be used in it will result in an engine that isn’t performing well and doesn’t satisfy the expectations of your customers.
Keep an eye on Valve Lift
A higher valve lift can open the valve even more so that more fuel mixture or air can pass through the valve. Valve lift is raised through the use of higher lobes on the camshaft, and/or more powerful rocker arms. Increased valve lift increases airflow up to a certain extent which is why you’ll want to increase the lift with the performance cam. The airflow then begins to diminish because of the restrictions in the cylinder head in the intake and exhaust systems. Any increase in the valve’s lift beyond this point is not worthwhile since there’s nothing to gain.
There are physical limitations regarding the distance the valves are able to be opened before it causes interference between the pistons and the valves and between the springs of the valve retention devices and tops of valve guides, and also between the valve springs’ coils. springs.
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Modifications are possible to improve the clearances (such as cutting deeper valve recesses in the tops of pistons, or reducing the elevation of the guides for the valves or lowering the spring seats) However, eventually the threshold is reached to where additional increases in lift of the valve can be physically achievable.
Today, many cams have “asymmetrical” grinds, which use different profiles for the downside and upside ramps that are on the cam’s lobes. They also have distinct lobes for intake valves and the exhaust valves.
Therefore, the best way of increasing the airflow further is to keep the valves open for longer (increase time) by opening them earlier before closing the valves later and/or by increasing the scavenging ability of the exhaust, which pulls air and fuel mixtures across the chamber of combustion, by increasing the overlap of the valves. There’s a lot of scientific research to determine the optimal valve lift and also how fast the valves close and open. Ideally, you’ll require a cam that is quick to open and close which opens and closes valves swiftly to ensure maximum the flow of air. Additionally, you’ll need the cam to hit the highest lift as fast as it is possible, though the mid-lift airflow is more influential on airflow overall due to the fact that it happens twice during every valve cycle (once when the valve opens, and then when the valve closes).
So, you’ll want cam lobes that can open the valves rapidly, hold the valves open at times when the flow of air is highest and then close the valves rapidly to reduce compression losses. For flat tappet cams the curve of the ramp located on one opposite side (flank) that opens the valve opening the valve must not be too steep, or the lifter might get stuck in the ramp. Similar to the opposite side of the lobe, the curvature shouldn’t be too steep or the lifter won’t follow the lobe’s path and bounce back down.
Roller cams are superior in this way because a roller located at the base of a lifter could be more radical in its shape of the lobe. The roller cam is able to open and close valves quicker, which means more airflow, while maintaining the same height and length.
Valve Timing Problems
Valve timing is the time where the intake valves are opened and close, and when the exhaust valves are opened and close. Out of these four timing events the closing of the intake valve is the most significant one, affecting how much power a specific camshaft produces. If the valve shuts down too quickly it could cause the cylinder to not fully fill in it’s intake stroke.
In the event that you open the intake valve longer permits more airflow to the cylinder, until a certain amount. When the valve for intake stays open beyond the point at which the piston has past the dead center of the bottom the upward motion of the piston could begin to reverse airflow and push air out through an intake port.
The time when the exhaust valve opens is the second most significant effect on the performance. If the valve is opened too quickly, the pressure in the cylinder could lose pressure before the valve has the chance to finish its job. If the valve for exhaust is opened too late in an exhaust cycle, this can increase the effort needed to pump to pull off the exhaust of the cylinder.
Closing the valve for expulsion, as well as that of the valve opening for intake as a result are the most insignificant on the performance. If the valve that shuts the exhaust valve is closed too fast, some air may remain inside the cylinder, which could alter the air/fuel mixture when the intake stroke follows. By keeping the valve open for longer (even when the intake valve begins to close) causes a scavenging effect that allows air to flow through the cylinder and into the exhaust. However, you shouldn’t have excessive overlap of the valve since this could deprive some of the mixture of fuel and air which would otherwise be inside the cylinder (it can also increase the emissions from exhaust).
In the case of an intake valve, the opening must to happen early enough that the cylinder can fill up with fuel mixture and air however if it begins to close too quickly (before the top dead center) you could have reversionary airflow returned to your intake manifold.
The exact point at which intake or exhaust valves are opened or close, is measured by ramps that are located on the cam lobes. When the follower or lifter is at the point at which the ramp begins from the base circle of the lobe The valvetrain starts to move and begins in the process of opening the valve. The point at which the valve opens can be measured at a certain quantity of lifting (such such as .004″ (or .050″) as well as referred to as being a number of millimeters of the rotation of the crankshaft.
For instance, a street cam could have a stated duration of 224 degrees for both the intake valve and the exhaust valve, measured with .050″ in lift with the maximum lift being .470″ (with the stock 1.5 in. ratio the rocker arm).
The lobe distance between the top lift points of valves for exhaust and intake may be between 110 and 120 degrees. The street cams as well as cams made to provide higher torque from the low to mid range generally have less overlap and greater the lobe separation. Cams made for maximum power at high speeds are more overlapping and have less separation between the lobes.
Confusion in Calculations
Comparing one grind to one that isn’t always easy since camshaft manufacturers typically measure their specifications for cams in different ways. If the duration is measured in .004″ of lift instead that .050″ of lift it increases the numbers, making the cam appear larger.
It is therefore important to know where lift is measured in comparing advertised camshaft specifications. In general, the longer the duration , the greater the rpm range at which the cam generates power. Cams with short durations are great for low speed acceleration and throttle response, while longer duration cams are ideal for high torque for high revving engines which need to produce a lot of top-end power.
Cams with durations ranging from range of 195-210 degrees (measured by .050″ the cam’s lift) generally considered to be the ideal for engines that are stock and models fitted with computerized engine controls. When you exceed 220 to 210 degrees of duration, the intake vacuum starts to fall. This can cause a disruption to idle quality and impacts the operation of computerized engines control systems.
Performance cams generally have durations that range from 220 to at least 280 degrees. The longer the duration, the more rough idle, and the greater the power range of the cam on the scale of rpm. A cam that has an idle time that is 240 degrees or higher will usually produce the greatest power between 3,500 and 7000 in rpm.
There’s more to the camshaft choice than just length and lift. Two cams made by two different manufacturers could have similar length and lift specifications but they will have very different characteristics in terms of performance due to their lobe profiles. Much of the work has been done to improve the lobes’ profiles in recent times to enhance the performance of cams, and a lot of cam manufacturers have released new products that reflect these changes.
Certain cam lobes could have ramps that are more or less steep that alter the speed of the valves opening and close. Rapid opening rates are good provided that the valvetrain and springs are strong enough to withstand the speed. Closing the valves swiftly is also beneficial, however, it is not when the valves close so quickly that they bounce when they are seated or the lifters follow the down slope in the lobe of cam.
A lot of cams today feature “asymmetrical” grinds, which use various profiles on the sides and the top ramps that the cam lobes have and also different lobes for inlet and exit valves. Some cams also have differently-groomed engines cylinders according to the location of the cylinder within the block of engine.
The end cylinders of an engine with only an intake manifold that is only one carburetor usually will benefit from a bit more length of a valve for the ends cylinders, to ensure that airflow is equalized into the intake manifold. This is a technique that NASCAR has been using for decades and is now offered in a few off-the-shelf lines of products.
Be a wise choice
Selecting a camera randomly from a catalog or on a website with hundreds or even dozens of grinds to choose from isn’t an easy task. The model you select might not produce the results you’re hoping for, so make sure to read the fine print on every grind, and then look over the recommended specifications. The manufacturer of the cam may state that the particular grind is best suited to specific piston, cylinder head and intake system configurations.
There are a variety of software programs available that will assist you in selecting a specific cam based on information you input into the software. The program will recommend a cam which is the most appropriate to the information you’ve entered. It can even plot simulated dyno torque and horsepower plots to show the performance of your engine you’re creating. Although they aren’t 100% exact, these programs perform a decent job of guiding you to the most appropriate cam.
The best option is to speak directly to the supplier of your cam when you are choosing the best camera. Many cam vendors will be more than willing to help you through the selection of a cam.
They can supply you with an extremely detailed questionnaire to fill in to pinpoint the specifics of your engine to ensure that a cam is selected that offers the most efficient performance all around for the vehicle you’re creating. Specifications cover all aspects of the engine, from displacement to head cylinders and compression ratios the exhaust and intake systems either naturally aspirated or enhanced, manual or automated transmission the torque converter’s stall speed and the gear ratios of manual transmissions and differential ratios, as well as the size of the tire to which kind of cam/lifter configuration you’d like (flat tappet roller, solid, or hydraulic) to details about how the engine is going to be utilized (street street/strip, circular tracks, drag racing off-roading, road racing, towing, pulling marine, RV or) in relation to the year/make/model as well as weight of the vehicle that the engine is to be put into.
If you’re seeking an advantage over your competition it’s possible to build an individual cam ground built for your engine.
It could also require additional specific information, such as airflow numbers for each step of lift through the cylinder heads rod diameters, strokes, the brands of rods, pistons or other components that are used, and so on.
The more detailed information you give to the manufacturer of the cam more they will be able to create a custom cam that is compatible with your engine.
Some cam companies have utilized data recording to improve the performance of a customized cam for a client. They connect the data logger with the intention of recording the engine’s speed while a vehicle is racing and analyze the speed of the engine through straights and through the corners to identify where the engine will require the greatest power.A Cam grind chosen to make the most power output at the speed range in which it truly needs it. A larger cam could produce more power overall however when the engine isn’t revving enough to make use of the extra power, it’s more cam than what the engine really requires.
It’s best to get an engine that works at the optimal rpm rather than selecting one that is able to produce huge numbers but does not perform well on the track.