Vtec Fuel Map: How Does It Change When Vtec Engages?

VTEC, or Variable Valve Timing and Lift Electronic Control, is a system developed by Honda to improve the performance of four-stroke internal combustion engines. VTEC provides the engine with valve timing optimised for both low- and high-RPM operations. The system uses two or three camshaft profiles and switches between them using hydraulic power. When discussing VTEC, it is important to consider whether the fuel map changes when it kicks in. Some sources suggest that the fuel map does change, resulting in more fuel being dumped into the engine. However, others argue that non-VTEC engines only have one cam profile for fuel mapping, which does not change.

VTEC fuel mapping

VTEC, or Variable Valve Timing & Lift Electronic Control, is a system developed by Honda to improve the performance of four-stroke internal combustion engines. VTEC fuel mapping refers to the process of adjusting the fuel settings on a vehicle's engine to optimise performance based on the number of camshaft profiles available. VTEC engines typically use two or three camshaft profiles, which are selected hydraulically, to deliver higher performance at high RPM and lower fuel consumption at low RPM.

The VTEC system provides the engine with valve timing optimised for both low- and high-RPM operations. It replaces the single cam lobe and follower/rocker arm of a conventional engine with a locking multi-part rocker arm and two cam profiles. One cam profile is optimised for low-RPM stability and fuel efficiency, while the other is designed to maximise high-RPM power output. The switching operation between the two cam lobes is controlled by the Engine Control Unit (ECU), which takes into account various factors such as engine oil pressure, engine temperature, vehicle speed, engine speed, and throttle position.

When running a VTEC head, the low cam typically operates on its own fuel mapping, separate from the high cam. This means that the fuel map does change when VTEC kicks in, as the ECU adjusts the fuel settings to match the selected camshaft profile. The ECU is programmed to switch from the low-lift to the high-lift cam lobes when certain conditions are met, such as engine load and speed. At the switch point, a solenoid is actuated, allowing oil pressure to operate a locking pin that binds the high-RPM rocker arm to the low-RPM one. From this point on, the valves open and close according to the high-lift profile, which opens the valve further and for a longer duration.

It is important to note that modifying the stock VTEC point without significant modifications to the engine can result in a loss of power. Additionally, VTEC fuel mapping may vary depending on the specific Honda model and engine type.

VTEC-E

For low RPMs, a normal engine's intake charge velocity is low enough that the fuel and air are not mixed very well. To compensate for the sub-optimal mixing effect, a slightly rich fuel-air mixture (more fuel) is needed to maintain smooth operation. VTEC-E artificially increases the intake charge velocity, creating a swirling effect inside the cylinder. This promotes a very good mixture of the fuel and air, thus allowing a lean fuel-air mixture to be used. The result is great fuel economy when running at low RPMs.

VTEC and fuel consumption

VTEC, or Variable Valve Timing & Lift Electronic Control, is a system developed by Honda to improve the performance of four-stroke internal combustion engines. It works by optimising valve timing for both low and high RPM operations. VTEC provides two camshaft profiles: one for low-RPM stability and fuel efficiency, and another for maximising high-RPM power output. The system is designed to combine low-RPM fuel efficiency with high-RPM performance.

The VTEC system uses a locking multi-part rocker arm and two cam profiles. The switching operation between the two cam lobes is controlled by the ECU, which takes into account engine oil pressure, engine temperature, vehicle speed, engine speed, and throttle position. When certain conditions are met, the ECU switches from the low-lift to the high-lift cam lobes, resulting in the valves opening and closing according to the high-lift profile, which opens the valve further and for a longer time. This increases the amount of fuel dumped, changing the fuel map.

The VTEC-E implementation is a variation of the SOHC VTEC, which increases combustion efficiency at low RPM while maintaining the mid-range performance of non-VTEC engines. VTEC-E uses two different intake cam profiles per cylinder: a mild cam lobe with little lift and a normal cam lobe with moderate lift. At low RPM, when VTEC is not engaged, one of the intake valves opens only a small amount, forcing most of the intake charge through the other valve with the normal cam lobe. This improves fuel atomization and allows for a leaner fuel mixture, optimising fuel efficiency.

The later VTEC-E implementations combine the fuel and low-RPM torque benefits of the earlier VTEC-E with the high performance of the original VTEC. These implementations use three intake cam lobes: two for low-RPM mode and one for powerful mode when the VTEC solenoid is activated. The lowest RPM for VTEC activation is 2500, and it may be higher if the load is weak. With the VTEC solenoid on, the third lobe pushes all the intake valves with a more aggressive profile, improving top-end power.

VTEC and engine performance

VTEC, or Variable Valve Timing and Lift Electronic Control, is a system developed by Honda to improve the performance of four-stroke internal combustion engines. VTEC works by optimising valve timing for both low and high RPM operations. This is achieved by using two or three camshaft profiles and hydraulically selecting between them. The system is designed to improve volumetric efficiency, resulting in higher performance at high RPMs and lower fuel consumption at low RPMs.

The VTEC system uses a locking multi-part rocker arm and two cam profiles. The first cam profile is optimised for low-RPM stability and fuel efficiency, while the second is designed to maximise high-RPM power output. The switching operation between the two cam lobes is controlled by the ECU, which takes into account various factors such as engine oil pressure, engine temperature, vehicle speed, engine speed, and throttle position. When certain conditions are met, the ECU triggers a switch from the low-lift to the high-lift cam lobes, resulting in improved valve opening and closing according to the high-lift profile.

The VTEC system is an improvement over standard VVT (variable valve timing) systems, which only change the valve timings without altering the camshaft profile or valve lift. VTEC provides a more flexible and efficient way to optimise engine performance at different RPM ranges.

In terms of engine performance, VTEC offers several benefits. Firstly, it improves high-RPM power output by maximising the valve lift and duration. This allows for increased airflow and fuel delivery to the cylinders, resulting in higher engine power and torque. Secondly, VTEC enhances low-end torque and fuel economy by optimising valve timing and lift at lower RPMs. This ensures a more efficient combustion process and reduces fuel consumption.

Additionally, VTEC technology can be combined with other engine features to further enhance performance. For example, VTEC can be integrated with Honda's VTC (Variable Timing Control), a continuously variable camshaft phasing system used on DOHC VTEC engines. This combination, known as i-VTEC, provides even greater control over valve timing and lift, resulting in improved torque output, especially at low and midrange RPMs.

VTEC and RPM

VTEC, or Variable Valve Timing & Lift Electronic Control, is a system developed by Honda to improve the performance of four-stroke internal combustion engines. It works by optimising valve timing for both low and high RPM operations. VTEC provides a single cam lobe and follower/rocker arm with two cam profiles: one for low-RPM stability and fuel efficiency, and the other for high-RPM power output.

The switch between the two cam lobes is controlled by the ECU, which takes into account various factors such as engine oil pressure, temperature, vehicle speed, engine speed, and throttle position. When certain conditions are met, the ECU switches from the low-lift to the high-lift cam lobes, resulting in the valves opening further and for a longer duration. This switch-over point is variable and determined by engine load.

VTEC-E is a variation of VTEC used in SOHC engines to increase combustion efficiency at low RPM while maintaining mid-range performance. It uses two different intake cam profiles per cylinder: a mild cam lobe with little lift and a normal cam lobe with moderate lift. At low RPM, one of the intake valves opens slightly due to the mild cam lobe, forcing most of the intake charge through the other valve with the normal cam lobe. This swirl of the intake charge improves air/fuel atomization, allowing for a leaner fuel mixture. When VTEC mode is engaged, both intake valves follow the normal camshaft lobe, resulting in identical performance to non-VTEC engines in the upper power band.

In summary, VTEC and RPM are closely related as VTEC provides optimised valve timing for both low and high RPM operations, resulting in improved performance and fuel efficiency. The system uses two cam profiles, with the ECU controlling the switch between them based on various engine parameters. VTEC-E, a variation of VTEC, further enhances combustion efficiency at low RPM while maintaining mid-range performance.

Frequently asked questions