What Is Vtec???

[Cammajamma77]

ok i know i will sound stupid posting this question but i want to know exactly what vtec is. how is a vtec different than a regular honda motor? the reason i am wondering is because my brother is saying that it is something that kicks in at a certain rpm for more power. i dont believe this but it may be true. wat exaclty is vtec? wat does it do?

[SteveDX89]

VTEC stands for Variable Valve Timing and Lift Electronic Control. The camshafts have two different profiles. One for low rpm operation and one for high rpm. An engine's demand for air and fuel are different at low and high rpms. Engines need more air-fuel at higher rpms to operate efficiently. The high rpm profile is more aggressive and allows the valves to open earlier and stay open longer to allow more of the air-fuel mixture into the cylinder. The VTEC point on stock cars is 5500 rpm, I believe. A camshaft with a high rpm profile will sputter at low rpms and a low rpm profile compromises some of the power at high rpms. VTEC is a way to have a profile for both.

P.S. This thread shouldn't be in Forced Induction forum.

[whtteg]

Originally Posted by SteveDX89

VTEC stands for Variable Valve Timing and Lift Electronic Control. The camshafts have two different profiles. One for low rpm operation and one for high rpm. An engine's demand for air and fuel are different at low and high rpms. Engines need more air-fuel at higher rpms to operate efficiently. The high rpm profile is more aggressive and allows the valves to open earlier and stay open longer to allow more of the air-fuel mixture into the cylinder. The VTEC point on stock cars is 5500 rpm, I believe. A camshaft with a high rpm profile will sputter at low rpms and a low rpm profile compromises some of the power at high rpms. VTEC is a way to have a profile for both.

P.S. This thread shouldn't be in Forced Induction forum.

This is correct but I will go alittle further into detail, as you know now the cams have 3 lobes for every cylinder, and there are 3 rocker arms. Now the two outside lobes are the low rpm profile, and the middle lobe is the high rpm profile. Now what happens is that the middle rocker arm just moves and does not push anything until at a certain rpm the ecu tells the VTEC solenoid to let oil pressure into the rocker arm assembly and this locks a pin between the middle rocker arm and the two outside rocker arms, now the vlaves are folloing the high rpm profile. In other words the middle rocker arn does not toucjh the valve instead it locks with the other two to run the high rpm profile. Maybe a pic to see will help here ya go