Updated: Feb 26, 2021
Simply put, motors are essentially big air pumps. The more air you can flow and pump through them, the more power they will make. One component that significantly affects how much air flows through a motor is it's cam shaft(s). Aftermarket cams are available to allow your motor to draw in more air, and to alter when (what RPM range) power is delivered.
Not only does a cam change how a car will perform, but it changes the sound as well. Power Delivery, as well as the notable "Chop Chop Chop" sound of a vehicle with an aggressive cam shaft has made cam swaps one of the most popular modifications. A cam itself is typically under $400, making a swap even more alluring.
Additionally, DOD / AFM / MDS vehicles commonly see lifter failures due to design flaws. When removing the failure prone components that allow a motor to run on half of its cylinders, a new cam shaft will be required as well. This is a common opportunity to install a more radical cam.
More valve lift adds power at the cost of extra valvetrain wear.
Longer duration cams add power at the cost of slightly more valvetrain wear.
Valve events that accentuate high RPM airflow will hinder low RPM performance.
Valve events that accentuate low RPM airflow will hinder high RPM performance.
Larger cams generate inherent drivability and emissions (odor) concerns.
New high-quality parts are needed for a reliable installation.
Your motor will be in disassembled and needs to be thoroughly cleaned.
Cam swaps, when performed correctly, are time consuming or expensive.
How do cam swaps make more power?
It is important to understand the mechanisms in which a cam allows the motor to bring in more air. With that knowledge, you can begin to understand the compromises and sacrifices involved with selecting a cam that you will be happy with.
Cams increase airflow in three ways:
The further you open a cylinder head's intake or exhaust valve, the more airflow the intake / exhaust port will be able to sustain. More airflow leads to more power. There is a point of diminishing returns when considering valve lift, as well as maximum amounts of lift that a cylinder head and valvetrain can physically support. More lift also means that a valve must ramp open further faster, putting added stress on your valvetrain. Practically speaking, more lift is power at the cost of extra valvetrain wear.
Another way to flow more air through your motor is to keep the valves open longer. By increasing the duration of a cam lobe, you are allowing cylinders more time to fill with air and fuel. While duration is important to consider, it is technically a byproduct of having the correct valve event timing for the type of power curve you are targeting. Longer duration cams add power at the cost of slightly more valvetrain wear.
Valve Event Timing
The point in the motor's rotation at which the intake and exhaust valves open and close has a strong effect on total airflow of a cam profile, as well as the RPM range where a motor will be efficient.
Valve events that accentuate high RPM airflow will hinder low RPM performance.
Valve events that accentuate low RPM airflow will hinder high RPM performance.
Cams are designed to do *one* thing well, while sacrificing elsewhere. Knowing how you plan to use your vehicle, as well as the sacrifices you are making, is crucial for choosing the RIGHT cam.
Loss of Low-End Torque
If you intend to drag race your vehicle, and care about all-out straight-line performance, you are likely spending most of your time in the higher RPM range. In this case, you would benefit from a cam designed for higher RPM operation. These are typically your "Stage (3 or 4)" cams.
With a "High RPM" cam that produces more peak horsepower, you will lose power and torque at lower RPMs. This is commonly masked in aftermarket cams, due to the additional increase in valve lift over a factory cam shaft.
With some of the larger "High RPM" aftermarket cams, you will overtly notice the power loss at lower RPMs. Steeper rear-end gears as well as aftermarket torque converters are suggested so that you do not spend as much time at the lower RPMs where the cam is inefficient.
At higher RPMs, you additionally may start to reach the flow limits of your intake manifold, inlet tube, cylinder heads, MAF, throttle body, or your exhaust. Without these supporting modifications, too large of a cam can end up performing worse than a smaller option.
Regardless which cam you choose, a larger cam will wear out your valvetrain quicker. The more extreme of a cam, the harder it is on your valves, valve seats, valve guides, valve springs, retainers, keepers, lifters, rockers / followers, push rods (if applicable), and timing components.
Aggressive ramp rates (the rate at which a valve opens or closes) necessitate heavier valve springs to keep the valve stem in contact with the rocker / follower as the cam rotates. Too light of a spring, and a valve will be prone to floating or bouncing off its seat. This can be destructive. Heavier springs add stability but put added stress and wear on your valvetrain components.
Another downside of heavier valve spring is that the metal they are made of is less resilient. Heavy valve springs are more prone to breaking and should be replaced at least every 10k-20k miles. Along with this, it is important to keep engine RPMs low on a cold motor, as the springs are more brittle at colder operating temperatures.
With many aftermarket cam shafts, you will lose gas mileage, as well as some drivability. A simple way to look at this is that if you have a cam that supports enough airflow for high RPM operation, the cam will also provide too much flow for low RPM operation.
Larger cams also generate less vacuum, due to the overlap between the intake and exhaust valves. This reduction in vacuum may be substantial enough to affect your vehicles systems. Brake boosters as well as many climate control systems rely on a strong vacuum source to operate correctly.
Raw Fuel Smell
Aggressive aftermarket cams will have more valve overlap than a factory cam. This means that when the intake valve opens, the exhaust valve is still open and is in the process of closing. With both valves open at the same time, some of the air from the intake manifold is drawn straight into the exhaust, from the low pressure wave generated by the last cycle's exhaust flowing out of the cylinder.
Carbureted, TBI, and Non-sequential port injection motors are constantly mixing fuel and air inside the intake manifold, regardless of what the valves may be doing at the time. Since fuel and air has already been mixed in the manifold of these types of motors, any air that is drawn through the intake and into the exhaust during the cam's overlap period will contain raw unburnt fuel. This smell is often noticeable and is unavoidable without very accurate and correctly tuned sequential injection.
Sequential Fuel Injection systems, with an injector at each port, can be calibrated to only spray fuel after the exhaust valve is closed. The short window of time, between when the exhaust valve closes and when the intake valve closes, is typically enough time to inject the correct amount of fuel at idle. This injection time window needs to be moved and adjusted based on your new cam profile. Above idle, however, we are relying on exhaust pressure, and resonance to keep un-burnt fuel in the cylinder.
Some raw fuel smell is always unavoidable with multi-point sequential injection. As much as we wish fuel injection were a clean and simple process, it is just not. During injection, some fuel condenses on the walls of your intake manifold. As soon as the intake valve opens, and pressure at the port drops, the condensed fuel evaporates and is drawn straight out of the exhaust.
A successful cam swap requires all parts of the motor to work correctly and in harmony with each other. A single part out of tolerance can easily cost a motor. Because of this, it is crucial to use good parts and install them correctly.
No two parts are created equally. While manufacturers of OEM parts have durability specifications that ensure their products will perform and last, the same cannot be said for the performance aftermarket. In a profit margin driven industry, distributors aim to deliver an acceptable quality at the lowest manufacturing cost.
Some parts, even if they are high quality, may not be correct (or correctly sized) for your application. You should be able to lean on the experience of your local performance shop for help finding the correct components for your cam swap, as well as most other modifications.
Many popular modifications are advocated for the wrong reasons. A good example of this is the upgraded trunnions for GM rockers. Popular offerings have well documented problems, yet they are still prolific due to popularity alone.
While you are in there…
To some extent, a cam swap is going to require your motor to be disassembled. With the motor disassembled, it is a good time to think ahead and replace components that wear out and fail. Examples of these parts include the timing chain, lifters, water pump, harmonic balancer, seals and gaskets, and many more.
With the added valvetrain wear from an aftermarket cam shaft, you may quickly push a used part past its mechanical limits. Because of this, it is important to thoroughly inspect and evaluate each removed component to decide if it makes sense to replace during the job.
At the end of the day, a car or truck is a huge metal conglomeration assembled by nuts and bolts. Some of the nuts and bolts need to be tightened to a precise amount, and in the correct order. Dirt, fluid, and debris that contaminate bolt holes during a cam swap can lead to incorrect torque, seized hardware, or worse, a cracked casting (block, head, etc.).
Time and care should be taken to ensure all load bearing bolt holes are clean, free of debris, and chased with a thread chaser before final installation. Failure to thoroughly complete this simple step can be a costly mistake.
Patience will be important when cleaning the decks of your block and cylinder head(s). Care should be taken to thoroughly remove all gasket material from surfaces, without scratching, gouging, or removing material from the substrate, leaving the surface uneven. For best results, the deck of cylinder heads can be resurfaced at a machine shop, to provide a better sealing surface.
During reassembly, some components need to be aligned with specialty tools to operate as they are designed. Often, the oil pump needs to be installed so that the pump gears are not riding on the housing during operation. Front and rear covers need to be centered with the crank shaft to prevent main seals from leaking.
Your choice of installation will be influenced by many factors, and only you can decide on how conclusive you want your cam swap to be. We live in a time of “$600 cam swaps”, and you truly get what you pay for. There are always tools and tricks that can make a cam swap easier and less time intensive. These shortcuts can have inherent risks. Timing chain "holders" (seen below) can come loose, dowels can allow lifters to fall into the crankcase, re-used parts can lead to failure, etc...
Do It yourself!
We have had a number customers complete successful cam swaps, with no prior experience; Some of whom were still teenagers at the time. With care and research, you can tackle a cam swap on your own. If you have the aptitude and time to commit to a project of this size, it can be worth your effort, so that you **KNOW** that the job will be completed to your specifications. If you are mechanically inclined, this is our suggestion for a cost-effective cam swap that has a good chance of being reliable.
Pay for a thorough swap
A thorough LS cam swap, including pulling the heads to replace lifters, takes upwards of 30 hours when thoroughly cleaning, inspecting, and installing components. This is not a cost-effective option but will safeguard you from having motor problems immediately after a swap.
Pay for a cheap swap
Sometimes a cheap cam swap makes sense. If you are starting with a junkyard motor or will replace your motor with another junkyard motor if (when) something fails, it probably does not make sense to spend four-figures on a cam swap. Professional shops are not going to tackle cheap cam swaps due to the job’s much higher failure rate, and it will be important to contrast the technician’s experience to your own abilities and patience.
We are here to support you regardless of which direction you decide to take. If the reliability concerns of a cheap cam swap do not sit well for you, and you cannot justify spending $4000 on 20-70whp, a supercharger may be a preferable option. Most supercharger manufacturers have kits designed to work on stock motors. These kits are only a bit more expensive than a high-quality cam swap and produce a significant amount more power. Most entry level blowers will be as reliable as a cam swap on an otherwise unmodified motor.
After your new cam is installed, you will need a custom tune to ensure your vehicle is calibrated for your new parts. The car’s ECU needs to be calibrated to correctly measure the extra airflow provided by your cam, so that it can proportionally inject more fuel as well. Additionally, the idle control routines that were designed for factory cams will cause the motor to surge and die. An un-tuned ECU also does not know that your new cam’s overlap period is allowing some of your motor’s idle airflow (and fuel) to escape out the exhaust.
Custom tuning will require your vehicle to be run at wide open throttle. On a fresh cam swap, we suggest a break-in tune to allow you to safely put some miles and a few heat cycles on your motor before final tuning. After you have worked out any problems and have changed your engine oil, it will be time to get your vehicle on the dyno for a complete final tune. It will be important to keep your tuning shop in the loop, as they may be scheduling weeks out for appointments. Future Modifications
It is important to consider what modifications you may want to pursue if the power gains of a cam are not enough to meet your goals. As a cam is only good at doing *ONE* thing well, it is important to consider whether it will work together with your future modifications.
A cam designed for High-RPM naturally aspirated power will work well with Nitrous but will not be appropriate to run with a turbo down the road. The exhaust (drive) pressure of a turbo motor is much higher than that of the intake manifold. With higher exhaust pressure, the cam’s overlap period will dilute the cylinder's incoming air-charge, leading to a loss of mid-range power.
As superchargers primarily increase pressure in the intake manifold and not the exhaust, they can sometimes work adequately with High-RPM NA cams. Overlap leads to some pressure loss out of the exhaust, and the increased intake to exhaust pressure differential pushes peak torque even higher in the RPM range. While not ideal, this trade-off may be okay with a positive displacement supercharger that makes full boost off-the-line. An aggressive cam and a centrifugal supercharger will often push peak power to a higher rpm range than desired. Conclusion Aftermarket cams sound awesome and are a crucial piece of the puzzle when putting together a high output engine. Our hope with this article is that we have helped you to understand some of the trade-offs related to picking the right cam for you. A cam is significant in defining the way your vehicle will perform and drive, and we want to give you as many tools as we can to build an engine setup that you are happy with. If you have questions, always feel welcome to reach out to us.