Mercedes Mullins
Fuel-injected engines, also known as EFI engines, differ from carbureted engines in terms of their camshaft requirements. Camshafts are an essential component of engines, featuring an overlap where both the intake and exhaust valves are open simultaneously, which can cause an unstable engine idle. While a carbureted engine may have a mechanical fuel pump and a distributor operated by the camshaft, a fuel-injected engine has different requirements. In a fuel-injected application, the camshaft must create a strong vacuum signal to function effectively without re-flashing the ECM (Engine Control Module) computer. This is achieved through specific camshaft grind requirements, which can vary depending on the engine and computer combination. Some engines, like late '80s-early '90s Chevrolets with a K engine code, have unique needs that may require consultation with a camshaft manufacturer. The addition of electronic fuel injection (EFI) can also impact the camshaft idle, resulting in a calmer and more stable idle but potentially losing the characteristic rumpy cam idle.
| Characteristics | Values |
|---|---|
| Camshaft in fuel-injected cars | Camshafts are present in fuel-injected cars |
| Camshaft function | Camshafts need to create a good vacuum signal to work in a fuel-injected application |
| Camshaft and fuel injection | The camshaft may not work at its optimum level with the stock fuel/timing curve programmed into the ECM unit |
| Overlap | All camshafts feature overlap, where both the intake and exhaust valves are open at the same time |
| Effect of overlap | The overlap can cause exhaust gas pressure to enter the intake manifold, mixing with fresh air and fuel, leading to an unstable engine idle |
| Calmer idle | Electronic Fuel Injection (EFI) helps calm the idle by damping manifold pressure swings with a MAP sensor, making the engine idle more stable |
| Customization | Custom EFI tuning is required for any major mechanical change to a fuel-injected engine |
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What You'll Learn
- Camshaft requirements differ for carbureted and fuel-injected engines
- Camshafts with a lot of overlap may be incompatible with factory electronics
- Fuel-injected engines may not work optimally with the stock fuel curve
- Camshafts require custom EFI tuning after major mechanical changes
- Camshafts with more overlap cause unstable engine idling
Camshaft requirements differ for carbureted and fuel-injected engines
Firstly, it is important to note that camshafts are indeed present in fuel-injected engines. The camshaft plays a crucial role in both carbureted and fuel-injected engines by controlling the opening and closing of the valves, allowing the engine to breathe and facilitating the combustion process.
One key difference in camshaft requirements arises from the distinct fuel delivery systems in carbureted and fuel-injected engines. Carbureted engines rely on a carburetor to mix air and fuel, which then enters the cylinders through the intake valves. In contrast, fuel-injected engines use fuel injectors to spray fuel directly into the cylinders or the intake tract. This difference in fuel delivery affects the camshaft's role in creating a vacuum signal, which is essential for proper engine operation.
To create an effective vacuum signal, a camshaft in a fuel-injected application must have a short duration, typically between 220 and 222 degrees @ .050. This is a critical requirement to ensure the fuel-injected engine functions optimally without the need to re-flash the ECM (Engine Control Module) computer. On the other hand, carbureted engines may have more flexibility in camshaft duration, but they often require careful tuning and jetting to achieve peak performance.
Additionally, the electronics used in the engine can impose limitations on camshaft requirements. Factory electronics in some engines may have limited tolerance for camshafts with a significant amount of overlap, which could necessitate compromises in camshaft selection. However, this limitation is not inherent to the fuel injection system itself but rather the specific electronics in use. Custom EFI tuning may be required when making major mechanical changes to a fuel-injected engine, impacting the camshaft's performance and requirements.
In summary, while both carbureted and fuel-injected engines utilise camshafts, the specific requirements for each type of engine differ. These differences are primarily driven by the distinct fuel delivery systems and the resulting vacuum signal needs. Understanding these nuances is essential when modifying or upgrading camshafts in carbureted or fuel-injected engines to ensure optimal performance and avoid potential issues.
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Camshafts with a lot of overlap may be incompatible with factory electronics
Fuel-injected engines have camshafts, and these camshafts need to create a good vacuum signal to work in a fuel-injected application. The camshaft's duration determines how long the intake/exhaust valve is open for, and therefore, it is a key factor in the amount of power that an engine produces. A longer duration can increase power at high engine speeds (RPM), but this can come with the trade-off of less torque being produced at low RPM.
Overlap is related to engine usage. Some overlap usually helps exhaust scavenging, but it can also bleed cylinder pressure. Increasing a camshaft's duration typically increases the overlap, unless the Lobe Separation Angle (LSA) is increased to compensate. A lay person can readily spot a long duration camshaft by observing the broad surface of the lobe where the cam pushes the valve open for a large number of degrees of crankshaft rotation. This will be visibly greater than the more pointed camshaft lobe bump observed on lower duration camshafts.
The LSA is the angle between the centre line of the intake lobes and the centre line of the exhaust lobes. A higher LSA reduces overlap, which improves idle quality and intake vacuum. However, using a wider LSA to compensate for excessive duration can reduce power and torque outputs. In general, the optimal LSA for a given engine is related to the ratio of the cylinder volume to the intake valve area.
While camshafts with a lot of overlap may be incompatible with factory electronics, this is not because of the "EFI" in and of itself. Custom EFI tuning is required on any major mechanical change to a fuel-injected engine.
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Fuel-injected engines may not work optimally with the stock fuel curve
Fuel injection is the introduction of fuel into an internal combustion engine, most commonly automotive engines, by means of a fuel injector. The term "fuel injection" comprises various distinct systems with fundamentally different functional principles. The only thing all fuel injection systems have in common is the absence of carburetion.
Fuel injectors enable an engine to generate maximum power while minimizing fuel consumption and reducing pollution. They can play a key role in the energy transition from fossil fuels to cleaner energy sources. By optimizing fuel consumption in traditional diesel engines and facilitating the operation of alternative fuel engines, fuel injectors contribute to trucking fleets' efforts to reduce carbon and greenhouse gas emissions.
For a camshaft to work in a fuel-injected application, it needs to make a good vacuum signal. While the camshaft may work with the stock fuel/timing curve programmed into the ECM unit, it will not be working at its optimum level. This can be likened to taking a performance carburetor out of the box, bolting it onto the engine, hooking up the fuel lines, and running it. It may run, but without tuning/jetting the carburetor to the engine, it will not work to its full potential.
There are some engines that you need to be wary of, such as late '80s-early '90s 350 Chevrolets with a K engine code and an idle speed of 500 rpm (TBI) and early Ford V8s with speed density fuel injection. These engines/computer combinations have very special camshaft grind requirements, so it is recommended to call your camshaft manufacturer for a recommendation.
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Camshafts require custom EFI tuning after major mechanical changes
Camshafts are a critical component of an engine, and any changes made to them can significantly impact the engine's performance. When it comes to fuel-injected engines, the camshaft plays a crucial role in creating a vacuum signal, which is necessary for the engine to function optimally. While a camshaft may work with the stock fuel/timing curve, it will not be operating at its maximum potential.
For those with fuel-injected engines, custom EFI tuning is often required after making significant mechanical changes, such as swapping out the camshaft. This is because the camshaft's profile directly affects the engine's volumetric efficiency, fuel consumption, and performance. By tuning the EFI system, you can ensure that the engine's fuel curve under boost closely matches its naturally aspirated shape, resulting in improved performance and fuel economy.
The process of custom EFI tuning involves calibrating the engine to achieve the desired balance between performance and fuel efficiency. When the engine is running at full power, the calibration can be adjusted to deliver optimal performance. On the other hand, during cruise situations, the "economy" part of the tune can take over, providing excellent fuel mileage. This versatility is one of the significant advantages of an EFI system.
Additionally, custom EFI tuning can address issues related to inlet manifold signal strength and vacuum fluctuations caused by large duration camshafts. By ensuring the ECU receives full battery voltage, you can maintain consistency in the engine's performance. It is also important to note that some factory electronics may have limitations in handling camshafts with a lot of overlap, which could require compromises in the camshaft design.
In conclusion, camshafts in fuel-injected engines require custom EFI tuning after major mechanical changes to ensure optimal performance, fuel efficiency, and engine longevity. By understanding the relationship between the camshaft and the EFI system, enthusiasts can make informed decisions when modifying their vehicles for improved power and efficiency.
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Camshafts with more overlap cause unstable engine idling
Fuel-injected engines require camshafts to create a vacuum signal to work in an application without re-flashing the ECM computer. Camshafts with more overlap can cause unstable engine idling. Overlap refers to the amount of time that both the intake and exhaust valves are open at the same time. More overlap can cause more lope, which is a choppier, rougher, or lumpy idle. This is because of reversion diluting the incoming charge and upsetting the carb signal. Lobe separation angle (LSA) is a by-product of the duration and overlap.
The amount of overlap on a camshaft can affect the performance of an engine. A camshaft with more overlap can increase power by making the engine more efficient at higher speeds. However, this comes at the cost of efficiency at lower speeds, which can cause the engine to run rough at idle. Very aggressive cams with a lot of overlap usually require a higher idle speed. The size of the carb and the type of intake manifold can also impact the performance of a camshaft with more overlap.
The trade-off between high and low-speed performance is a common theme when discussing camshafts and engine performance. Engines are designed to either maximize power at high RPM or be well-rounded and perform efficiently at low RPM. A well-running engine that idles smoothly will not have as much power as one that is tuned for high-power output. Honda's V-tech engine uses two different cam profiles to balance high power output and low RPM performance.
Some engines, such as those in motorcycles, are less susceptible to the effects of overlap on idle characteristics. Motorcycle engines with individual throttle bodies can have smoother part-throttle power delivery, which is important for rider safety. Additionally, factory electronics may have limitations on how tolerant they are of camshafts with a lot of overlap, which can require compromises on camshaft design.
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Frequently asked questions
Yes, fuel-injected cars have a camshaft.
All else being the same with the engines, there shouldn't be a difference in camshafts. However, if you are using factory electronics, there are limitations with how tolerant they are of camshafts with a lot of overlap.
Calmer idle characteristics occur for a variety of reasons. EFI helps to calm the idle, making it more stable.
