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When driving normally, the need for power might not be so obvious, but when overtaking, whether the power is sufficient becomes crucial.
Many drivers have mentioned that their car used to have decent power for overtaking, but lately it feels like the car lacks the strength to do so. What could be causing this?
How many seconds does it take to safely overtake?
First and foremost, overtaking must be done safely. In fact, there is a safe overtaking time—the duration required to complete the maneuver—which directly influences the accident rate during overtaking. This safe overtaking time varies depending on the maximum speed limit of the road.
Data on overtaking accidents was presented at the 2016 International Conference on Information and Knowledge Technology. For instance, when the speed limit is between 50 and 70 kilometers per hour, completing the overtaking maneuver in approximately 9 seconds results in the lowest accident rate.
The time required for safe overtaking is 7 to 9 seconds, but the period that truly tests a vehicle’s power during overtaking lasts only 2.8 seconds. This interval is also referred to as the acceleration phase in automotive overtaking research.
How much should the vehicle’s speed be increased during this period?
The required speed increase for overtaking varies between urban and highway conditions.
According to the Highway Overtaking Speed and Overtaken Speed Chart, when overtaking on national highways and expressways at speeds exceeding 60 km/h, the speed differential must be at least 20 km/h.
Urban driving speeds are relatively low, and the minimum speed difference required for overtaking is also small, at only 12.5 kilometers per hour. However, there’s a special case for overtaking in urban areas: when there are only two lanes, overtaking requires borrowing the oncoming lane to avoid collisions with oncoming traffic. Therefore, the vehicle must accelerate more aggressively.
On two-lane highways, overtaking should be very easy, requiring a speed difference of around 30 kilometers per hour.
How much power does a vehicle need to overtake safely?
In general, to overtake smoothly, a standard road requires acceleration of 30 km/h within 2.8 seconds, while a highway requires 20 km/h within 2.8 seconds.
A vehicle’s acceleration is typically measured in G-force. One G equals one times the acceleration due to gravity, equivalent to 9.8 meters per second squared.
This acceleration level translates to approximately 0.3G in urban driving and 0.2G on highways.
Common examples include the Volkswagen Golf 1.6L automatic and Chevrolet Cruze, with an average acceleration of 0.2G.
Cars achieving 0.3G in urban driving and 0.2G on highways—like the 1.5T Honda Civic, 1.5T Volkswagen Lavida, and 2.0L naturally aspirated Mazda CX-4—record 0-100 km/h acceleration times between 9 and 10 seconds in real-world testing.
Vehicles achieving this acceleration level on the market are typically equipped with either a 1.5T or 2.0L naturally aspirated engine, priced slightly above 100,000 yuan.
What should I do if my car feels underpowered after driving it for a long time?
If you feel your car used to have decent power when overtaking but now lacks punch during passing maneuvers, it might be due to carbon buildup. Some experienced drivers claim that flooring the accelerator twice while stationary can clear carbon deposits, but this isn’t entirely accurate.
While flooring the throttle can remove carbon buildup, it’s not suitable for all vehicle models. Moreover, improper technique can actually worsen carbon accumulation.
So where did this idea of clearing carbon deposits by revving the engine come from? It originates from Volkswagen’s US patent US6866031B2, “Direct Injection Internal Combustion Engine.” The patent states that operating the engine at over 3000 RPM for 20 minutes can remove a layer of thick carbon deposits.
However, there are two conditions: first, the engine speed must exceed 3000 RPM, and second, it must be sustained for 20 minutes. Controlling the RPM is challenging—if you press the accelerator a bit harder, the RPM instantly surges past the redline; then, when you ease off the throttle, it immediately drops below 3000 RPM.
Failure to maintain stable RPM not only prevents carbon deposits from being cleared but may actually increase them. Hu Xinqiang’s master’s thesis from Hebei University of Technology, titled “Research on ECU Technology for Gasoline Engine Electronic Fuel Injection Systems,” explains that during heavy throttle application—such as rapid acceleration or exceeding the redline—the onboard computer increases fuel injection by 10% to 30% to enrich the air-fuel mixture.
This way, when you floor the throttle in neutral, fuel injection increases instantly. Conversely, if you only partially depress the throttle, valve opening instantly decreases, leading to insufficient air intake. The excess fuel that isn’t fully burned contributes to increased carbon buildup.
Additionally, some vehicles have fuel cutoff protection systems, making it impossible to floor the throttle in neutral. When the vehicle is in neutral or park (P), the engine control unit (ECU) will cut fuel supply once the RPM reaches a certain threshold—typically around 3000 RPM. So if you rev the engine in neutral and the RPM exceeds 3000, the system will abruptly cut fuel. Forget about sustaining it for 20 minutes—even keeping it going for a minute is difficult, making it impossible to effectively clean carbon deposits.
How can I restore the power needed for overtaking?
So how can carbon deposits be effectively cleaned? Jiang Jing and colleagues summarized the current methods for removing carbon deposits from engines in their article “Exploration of New Methods for Treating Carbon Deposits in Automotive Engines,” published in the journal Equipment Manufacturing Technology.
First is the disassembly method. This involves completely dismantling the engine to thoroughly clean the internal carbon deposits. While this approach achieves the most thorough cleaning, it is time-consuming and labor-intensive. Additionally, it can compromise engine sealing integrity and adversely affect engine performance.
Another approach is non-disassembly cleaning. This involves injecting chemical agents into the engine or using gasoline detergents like fuel additives to dissolve carbon deposits. Additional methods include utilizing newer technologies such as ultrasonic cleaning or high-purity hydrogen.
Among these carbon deposit removal techniques, I recommend fuel additives. They eliminate the need for engine disassembly and can be conveniently added during routine refueling—simply pour one bottle into the tank.
