The internal combustion engine is a marvel of engineering. In the quest to gain more power beyond bolt-on modifications, the next step is to look inside the motor. However, this is not so straightforward and can get quite expensive in short order.
For starters, replacing a camshaft or crankshaft is not like adding an intake or exhaust. It involves a fair amount of research along with weighing the pros and cons. This is especially true for a camshaft, because you need to account for several things. Things like supporting modifications and intended use are important factors to look at when replacing a camshaft. Many people often think bigger is better but choosing the wrong one can actually hurt performance, not improve it. Suffice to say, it is more than simply ordering a camshaft and stuffing it in your motor.
While adding a different crankshaft will not necessarily add horsepower (excluding longer throw, or stroker crankshafts) it can affect the engine’s operation. Generally speaking, replacing the crankshaft does not come into consideration unless you are building a race or high horsepower motor. Likewise, it is a costly component, usually well over a thousand dollars, especially for a forged or billet crankshaft. For the most part, street applications will not require one as other components inside the engine, like the connecting rods and pistons, are likely to give out first.
With that said, we will cover the camshaft and crankshaft, how they work, and when you should consider replacing them.
Depending on the configuration, overhead valve (OHV), overhead camshaft (OHC), or dual overhead camshaft (DOHC), an OHV will have one camshaft, OHC one or two, and DOHC two or four.
The camshaft is a metal rod made from cast iron or billet steel and has egg-shaped lobes. While an OHV setup has a few more components than an OHC or DOHC setup, the end result is the same, with the camshaft controlling the opening and closing of the intake and exhaust valves.
In simple terms, a four-stroke engine has four cycles: intake, compression, combustion, and exhaust. During the intake stroke, a lobe on the camshaft opens the intake valve(s), so air and fuel can enter the cylinder. For compression and combustion, the valve(s) remain closed, and during the exhaust stroke, another lobe opens the exhaust valve(s), and the exhaust gases exit the combustion chamber.
Performance Upgrade Potential
A “hotter” or performance camshaft can really wake an engine up. This is especially true if there are supporting modifications that improve the intake and exhaust flow like a cold air intake, a better flowing intake manifold and/or cylinder heads, headers, and exhaust. If so, gains of 50 or more horsepower are not unreasonable, especially for a larger engine. However, there are a few things to take into account before replacing the camshaft.
Fuel Economy and Driveability
While a mild camshaft will have a minimal impact on fuel economy and may slightly increase it, more aggressive profiles typically cause the opposite. Not to mention, they can affect driveability in the form of a poor idle and produce less low-end horsepower and torque. However, on many newer cars, tuning can mitigate some of the negative effects.
Street or Track?
Many camshaft manufacturers offer multiple profiles, so it’s important for you to pair it with your existing modifications. For street use, a camshaft should have a powerband that covers the mid RPM range as most driving is at lower speeds. For a track vehicle, especially for high-speed driving, the powerband should be in the mid and high RPM range.
Granted, this is not a popular topic, but some performance camshafts may not be emissions legal. Of course, this varies to some extent, but if this is a daily driver, it is something to take into account.
Lastly, manufacturers optimize their modern engines very well compared to old engines. In other words, changing the camshaft may only yield minimal gains of less than 20 horsepower. While that is decent for some, it should be noted many performance engines are DOHC which means a V6 or V8 will have four camshafts. In terms of parts alone, this can easily exceed $1,000, not to mention installation costs. If you plan on having it installed at a shop, it can be double that. Suffice to say, it becomes a question of whether or not it is worth it to spend several thousand dollars for a 15 horsepower gain.
You can think of the crankshaft as the backbone of your engine. In fact, it is arguably the most important and costly component of the motor itself. Sparing the physics lesson, it converts the up and down motion that results from the combustion process into rotational energy. The transmission transfer the rotation energy and send it to the drive axle, which drives the wheels.
Like the camshaft, the four cycles must be perfectly timed with the valves to prevent contact with the pistons. This can occur several thousand times a minute depending on the engine speed. This is where the name “revolutions per minute” or “RPM” comes from. Suffice to say, a crankshaft needs to be constructed of durable materials and properly balanced in order to prevent the motor from self-destructing in short order. As such, it goes without saying that oil is the lifeblood of an engine, and not changing it frequently will ruin the bearings and crankshaft in short order.
The Three Types of Crankshafts
- Cast: This is the most common type of crankshaft to use, especially in naturally aspirated engines. In simple terms, molten iron or steel is poured into a casting, allowed to cool, and then machined to spec. Obviously, the strength will vary considerably depending on the materials used and the casting process, although many cast crankshafts can usually handle between 300-500 horsepower, and for most street applications, this is usually sufficient.
- Forged: In this process, heavy machines press and shape the the alloys, which are then machined into form. The end result is a much stronger crankshaft, and it is typically used in many high horsepower and forced-induction motors. Likewise, it is a good upgrade over a cast crankshaft in terms of durability and longevity, and many can handle well over 1,000 horsepower. For the vast majority of applications, a forged crankshaft is more than enough.
- Billet: A billet crankshaft starts its life from a solid chunk of forged steel, although it is CNC machined into form. They are even more durable than a forged crankshaft and considerably more expensive. For the most part, billet crankshafts are only used in purpose-built race motors.
Performance Upgrade Potential
In most applications, replacing the crankshaft is not even a question unless you are building a performance motor. Simply put, it is not a bolt-on modification as it involves complete disassembly of the engine itself. Not to mention, forged, or billet crankshafts typically cost well over $1,000. Even for a moderate engine build, a cast crankshaft is usually sufficient unless you plan on pushing a considerable amount of power or will be driving it on the track.
Where a crankshaft upgrade can yield sizable gains is if you are building a stroker motor. A stroker motor uses a crankshaft with a longer throw. A longer throw means there is more distance between the bottom and top dead center, which increases displacement. Increased displacement creates more horsepower and torque. As such, stroker crankshafts are available for many applications, and they are a popular upgrade in the quest for producing more power.
Should I Upgrade My Camshaft or Crankshaft?
It really comes down to usage, and we’ll start with the simpler of the two, the crankshaft. Unless you are building a high horsepower race motor, a cast crankshaft will sufficient for most naturally aspirated applications. However, a forged crankshaft is a good upgrade for performance and race engines, especially for forced induction. For the most part, a billet crankshaft should not come into consideration unless you are building a purpose-built race motor.
On the other hand, changing your camshaft can lead to sizable performance gains. That being said, you shouldn’t install a camshaft as your first modification. You can see greater gains from first installing supporting modifications like an intake and exhaust. In addition to that, choosing the right camshaft involves quite a bit of research. You need to account for things such as usage, target RPM range, and power adders. Not to mention how it will affect driveability, fuel economy, and emissions. Lastly, there is the cost-to-benefit factor, and for many newer vehicles, the gains may not justify the cost.
With that said, building a motor is a well-thought-out and expensive process. Just a cam and crankshaft alone can easily cost several thousand dollars. If you add the other components of an engine build like pistons, connecting rods, etc, that figure goes up considerably. If you decide to build your motor, a forged crankshaft is a solid foundation, paired with a good performance camshaft, it can really increase performance.