What is i-VTEC?

Over time Honda have implemented a few variations of the VTEC system and have managed to achieve some great results. The most common VTEC system is the DOHC (Double Overhead Cam) system where each set of valves (Intake and Exhaust) has its own cam. DOHC VTEC configuration is optimised for high power output, and is capable of making upto 88kW per litre (as found in the current S2000).

The second impementation of VTEC is that of SOHC VTEC where both sets of intake and exhaust valves are run via a single cam. This mechanism is not for performance but for economy, while still making good power for practical everyday use. With SOHC VTEC, only the intake valves benefit from higher lift and not the exhaust valves.

The latest impementation of VTEC is that of i-VTEC where the system allows continuasly variable valve timing over the rev range (presently only on the intake cam) which allows for upto 6kW more at peak power with improved torque and fuel efficiency.

i- VTEC also has the added flexibility that it can adjust intake cam timing depending on engine load using a combination of inputs from the TPS, vehicle speed and vacuum readings.

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Originally Posted by wynode

Over time Honda have implemented a few variations of the VTEC system and have managed to achieve some great results. The most common VTEC system is the DOHC (Double Overhead Cam) system where each set of valves (Intake and Exhaust) has its own cam. DOHC VTEC configuration is optimised for high power output, and is capable of making upto 88kW per litre (as found in the current S2000).

The second impementation of VTEC is that of SOHC VTEC where both sets of intake and exhaust valves are run via a single cam. This mechanism is not for performance but for economy, while still making good power for practical everyday use. With SOHC VTEC, only the intake valves benefit from higher lift and not the exhaust valves.

The latest impementation of VTEC is that of i-VTEC where the system allows continuasly variable valve timing over the rev range (presently only on the intake cam) which allows for upto 6kW more at peak power with improved torque and fuel efficiency.

i- VTEC also has the added flexibility that it can adjust intake cam timing depending on engine load using a combination of inputs from the TPS, vehicle speed and vacuum readings.

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This is all true, although there is now another form of 'vtec'. The other form of vtec I am refering to is not for power gains, nor is it really for economy gains. It is found on the Civic Hybrid and is deemed vtec (variable valve timing and lift)

How it works is by locking the exhaust valves slightly open on cyl 2, 3, and 4 to reduce the amount of engine braking. All principles and theories of vtec are used in this system but they are used to achieve a totally different result.


FastAz

to put this simply,
As far as I am aware, ivtec means vtec will kick in at a variable level depending on the amount of acceleration.... whereas normal vtec engines are set to a specific rpm or rough area
correct me if im wrong.
Sean

Quote:

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Originally Posted by FAT VTI

to put this simply,
As far as I am aware, ivtec means vtec will kick in at a variable level depending on the amount of acceleration.... whereas normal vtec engines are set to a specific rpm or rough area
correct me if im wrong.
Sean

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An i-VTEC engine has two VTEC functions:

1) The normal VTEC system which engages the high output CAM lobes at a fixed RPM (same as a B16A for example). The ECU cannot change the engagement RPM, but it can choose not to engage VTEC if, for example, the oil pressure is too low.

2) The ECU can change the CAM gear angle to "fine tune" the valve timing. This means the ECU can let more fuel and air in to gain power at high RPM or hard acceleration, or decrease the fuel and air for economy or low RPM torque. This function is variable and not necessarily dependent on the RPM. The ECU decides what angle is most beneficial depending on numerous variables.

Another function of i-VTEC is the reduction of pumping loss. Basically it's a work-around to avoid turbulent airflow recirculation forming through the narrow gap of a partially open throttle valve.
Instead of partially opening the throttle valve at low speeds, the drive by wire opens it completely, or at least opens it far more than a conventional throttle valve. It, in effect allows free flow of air / fuel into the cylinder. In order to control how much fuel is burnt, the valve timing on the cylinder is delayed on the compression stroke. It literally sucks in a full cylinder-load of fuel/air and then squirts some of it back out, depending on throttle position, before combustion.