taken from Articles (All About VTEC) In order for the ECU to initiate the VTEC system, 5 engine conditions must be met. Temperature: The engine must have reached normal operating temperature. Throttle Position: The throttle must be open far enough to allow for increased airflow in VTEC. Vehicle Speed: The car must be in motion (wheels spinning).
The best way to tell if your car's VTEC system is engaged is to listen to the engine. When you rev the engine, you should hear a distinctive "bwaaah" sound that indicates the VTEC system is engaged and working. Another way to tell is to look at the tachometer. If the needle moves into the red zone when you rev the engine, that's an indication
Not all VVT uses the same method for varying timing. VTEC is trademarked by Honda and it varies the lift by using different cam lobes. You can vary the lift without changing the valve timing and you can also vary the timing using the same lobe, without changing the lift by using a phaser. Different manufacturers choose different methods.
This works with the K20a3, K24a1, K24a4 and K24a8 engines with the non I rundown the different options for rockers with a Vtec Killer cam setup on my K24a1. This works with the K20a3, K24a1 The amount of horsepower that VTEC can add to an engine varies based on the model and setup, but it is typically around 10-15 horsepower. The power gains come from the increased air flow, which can be used to increase the RPM range. The higher the RPM range, the more power the engine can produce. VTEC or Valve Timing Electronic Control is a system that's been used by Honda in passenger cars since 1991. I believe the 1991 NSX was the first production v SJDaZ. 380 693 646 818 758 349 695 306

how does a vtec engine work