The choice of a camera can cause anyone a headache , especially in the event that they pick the wrong model for a particular application. There’s lots of science involved in the selection of 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 set across the length. Each lobe opens and shuts the valve by shifting the pushrod, lifter and rocker arm. Or in the case of an overhead cam motor, by the movement of a cam follower or directly valve action.
The shape, size and location of the camshaft’s lobes determine the timing of the valve and compression, as well as the engine’s breathing characteristics. This affects the engine’s potential performance and the range of rpm at which the engine can produce the most torque and power.
The selection of to select the “right” camshaft thus it is not just the primary element of building an engine that performs well, but it is also the mainstay. The cam is the engine’s foundation and is the primary factor that determines the other components that must be selected to build your engine (cylinder heads pistons, valvetrains inlet and exhaust pipes along with carburetion).
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 right cam to give you the performance you desire is to identify the range of rpm at which your engine will produce the greatest power, then select one that is compatible with the characteristics of breathing in the head of the cylinder, the exhaust and intake manifolds, the weight and the gearing of the vehicle it will be running in.
If you’re building a massive stroker motor to be used in the ProStock drag car, with an aftermarket 500-600 cubic inch block, and the cylinder heads have ports of the size of a fist that can flow more than 500 cfm with .900″ the valve height, the engine will require a huge cam with plenty of lift in the valve, length, and overlap.
However If you’re building a smaller street-performance block intended to be a daily driver using auto transmissions and 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 rpms as well as a split-plenum, 180-degree hi-rise intake manifold, and a properly-sized carburetor.
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Don’t overdo your work
The biggest error that engineers make when designing engines is to overcame an engine. Utilizing a cam with too much lift in the valve or duration, and/or excessive overlap of valves for the intended application could have negative effects.
Everyone loves big numbers, but if the specs for the cam aren’t in line with the engine you’re developing or the kind of application the engine is being used for You’ll end up with an engine that isn’t performing well and does not satisfy the expectations of your customers.
Keep Your Eyes on Valve Lift
The higher the valve lift, the valve more, allowing for more fuel mixture or air can pass through the valve. The valve lift can be increased through the use of higher lobes on the camshaft or more powerful rocker arms. The higher the valve lift, the better the airflow to a certain point that you need more lift from an engineered cam. The airflow then begins to diminish due to the limitations within the cylinder head, in the intake and exhaust systems. Any increase in the valve’s lift beyond the point of no return is ineffective since there’s nothing to gain.
There are physical limitations regarding the distance the valves are able to be opened before it causes interference issues between the pistons and the valves and between the springs of the valve retention devices and tops of valve guides, as well as between the valve springs’ coils. springs.
Modifications are possible to improve the clearances (such as cutting bigger valve recesses into the tops pistons, or reducing the size of the valve guides and/or lowering the seat of the springs) However, eventually the limit will be reached, beyond where further increases in the lift of valves are physically feasible.
A lot of cams today feature “asymmetrical” grinds, which use different profiles for the downside and upside ramps on the cam’s the lobes. There are also different lobes to accommodate intake valves and the exhaust valves.
The sole way to boost the airflow further is to keep the valves open for longer (increase the duration) by opening them earlier before closing the valves later or by enhancing 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 which determines the ideal valve lift and the speed at which valves close and open. Ideally, you’ll require a cam that is quick to open and close that closes and opens the valves rapidly to increase the flow of air. Also, you would like the cam to reach maximum lift as fast as you can, even though the airflow in mid-lift is more influential on the total flow of air due to the fact that it happens twice during every valve cycle (once when the valve opens and once when the valve closes).
Therefore, you need cam lobes that can open the valves swiftly, keep the valves open at times when the flow of air is highest and then close the valves swiftly so that compression losses are minimized. For flat tappet cams the curve of the ramp that is on the opposite side (flank) that opens the valve which opens the valve must not be too steep, or the lifter could be able to dig into 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 , but bounce back down.
Roller cams are superior in this regard because a roller located at the base of a lifter could have a more radical contour 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
Timing of valves includes the times where the intake valves are opened and close, and when the exhaust valves are opened and close. From these four timings closing the intake valve is the most significant one, affecting how much power a specific camshaft can generate. If the intake valve is closed too quickly it could cause the cylinder to not be filled completely with it’s intake stroke.
The intake valve being open longer permits more airflow to the cylinder, until a certain amount. In the event that the intake valve is open beyond the point at which the piston has past the dead center of the bottom the upward movement of the piston may begin to reverse the flow of air and push it back out from an intake port.
The time when the exhaust valve opens is the second biggest influence on its performance. If the valve for exhaust opens too quickly, the pressure in the cylinder could lose pressure before the valve is able to be able to complete its task. If the valve for exhaust is opened too late in an exhaust cycle, this can increase the effort needed to pump to force away the exhaust from the cylinder.
Closing the valve for expulsion, as well as that of the valve opening for intake in contrast will have the least effect on the performance. If the valve that shuts the exhaust valve is closed too fast, some exhaust could remain in the cylinder, and may alter the air/fuel mixture when the intake stroke follows. By keeping the valve open for longer (even when the intake valve is beginning to close) results in a scavenging process which helps draw air through the cylinder and into the exhaust, however it is not recommended to have excessive overlap of the valve since this could deprive part of the fuel/air mixture that could otherwise stay inside the cylinder (it will also cause an increase in emission from exhaust).
Opening of the intake valve needs to happen early enough that the cylinder is able to fill up with fuel mixture and air however if it begins to open too early (before the dead center of the top) you could receive reversionary airflow into your intake manifold.
The exact point at which intake valve and the exhaust valve are opened to close can be determined using ramps on the lobes of the cam. Once the follower or the lifter reach the point at which the ramp is located from the base circle of the lobe the valvetrain starts to move and begins in the process of opening the valve. The point of opening can be determined at a specific level of elevation (such such as .004″ (or .050″) as well as is listed as being a number of degree of rotation on the crankshaft.
For instance, a street cam could have a stated duration of 224 degrees for both the intake or exhaust valves that are measured by .050″ in lift with an upper limit of .470″ (with the stock 1.5 proportion arm rockers).
The lobe distance between the top lift points of valves for exhaust and intake may be as high as 110 degrees. Cams, street cams or other models made to provide higher torque from the low to mid range generally are less overlapped and have more the lobe separation. Cams specifically designed for maximum power at high speeds are more overlapping and have less separation between the lobes.
Confusion in Calculations
Comparing one cam grind with 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, rather as .050″ in lift, this will increase the numbers, making the cam appear larger.
Therefore, it’s crucial to determine the point at which lift is measured in comparing advertised camshaft specifications. The longer the duration , the greater the rpm range in which the cam generates power. Cams with short durations are great for low speed acceleration and throttle response, while long duration cams work best for large for high revving engines that require to produce a lot of top-end power.
Cams that have durations in the range of 195-210 degrees (measured by .050″ Cam lift) are generally considered the ideal for engines that are stock as well as those equipped fitted with computerized engine controls. If you go above the 210-220 degree duration, the intake vacuum starts to fall. This can cause a disruption to idle quality and can affect the performance of computerized engines control systems.
The duration of performance cams is typically between 220 and the 280 degree mark or more. The longer the duration, the more rough the idle and also the more 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 choosing a camshaft than 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 focused on re-designing the lobes’ profiles in recent times to improve the performance of cams, and a lot of cam manufacturers have released new products which reflect these advancements.
Certain cam lobes might have ramps that are more or less steep to alter the speed of the valves opening and close. Rapid opening rates are good so long as the valvetrain and springs are strong enough to withstand the speed. The ability to close the valves fast is also a good thing, however it’s not when the valves close so quickly that they bounce when they touch their seats, or the lifters follow the down slope in the lobe of cam.
A lot of cams today feature “asymmetrical” grinds that employ distinct profiles to create the sides and the top ramps that the cam lobes have and also different lobes for intake valve and the exhaust valve. Certain cams have differently-groomed engines cylinders according to the position 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 time for the valves on the end cylinders in order to even out the flow of air into the intake manifold. This is a technique that NASCAR has employed for many decades and is now offered in a few off-the-shelf lines of products.
Make the Right 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 choice of cam might not produce the results you’re looking for, which is why it’s important to read the fine print on every grind, and then look over the recommended specifications. The supplier of the cam might state it is the best fit for specific cylinder heads, pistons and intake system configurations.
There are a variety of software programs available to aid you in choosing a camera based on the data you input into the software. The program will recommend a cam that is most compatible with the data that you’ve inputted, and will also plot simulated power and torque graphs of the motor you’re creating. While not 100% exact, these programs are pretty effective of guiding you to the most appropriate cam.
The most effective method however is to directly contact an online supplier when selecting the best camera. Many cam vendors will be more than willing to help you through the selection of a cam.
They will provide you with a comprehensive questionnaire that you can fill out to determine the details of your engine to help you choose a cam chosen to provide the highest performance across all aspects of the vehicle you’re creating. The details comprise every aspect of engine displacement to head cylinders and compression ratios the exhaust and intake systems whether naturally aspirated or enhanced, manual or automated transmission the torque converter’s stall speed and manually-operated transmission ratios and differential ratios, as well as the size of the tire to which kind of lifter/cam setup you’d like (flat tappet roller, solid, or hydraulic) to details about how the engine is going to be employed (street street/strip, circular race track off-roading, road racing, towing, pulling marine, RV or) according to the year, make and model as well as the weight of the vehicle that the engine is to be put into.
If you’re looking to gain an advantage over your competition You could opt 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 details you give the supplier of your cam more they will be able to create a custom cam that is compatible with your engine.
Certain cam manufacturers have employed data recording to enhance the custom camera for a client. They connect the data logger with the intention of recording the engine’s speed while a vehicle is racing and then analyse the speed of the engine through straights as well as into and out of the corners to identify where the engine will require the greatest power.A grinding of the cam is selected to maximize engine power output at the speed range in which the engine really requires it. A larger cam could produce more power overall but in the event that the engine doesn’t rev sufficiently to benefit of that additional power, it’s more cam than what the engine actually requires.
It is better to choose an engine that works within the optimal rpm range instead of selecting one that is able to produce huge numbers but does not make it to the top of the track.