The VTEC system used in a S2000 opens 2 intake and 2 exhaust valves, whenever the valves are opened. Other SOHC VTEC systems operate only 1 intake valve on the "low RPM" cam profile and 2 intake valves on the "high RPM" cam profile.

Valve lift and duration are optimized for Maximum power at all RPM's by using the VTEC when the engine requires more Air at high RPM. Turning on the high RPM cam profile at low RPM will loose power.

 

Why wouldn't you want higher valve lift at lower RPM's? Why would the engine bog down at low RPM's when giving it more air if you are measureing a/f correctly? Does this come into the whole tuning issue? If you tuned it correctly, could you theoretically produce more output at low RPM's all the way through the high's?

 

there's a limit to how low you can go.

the hondata reflash for my06+ with toda header reduces it to 4500.

realize tho, that a cam made to breathe to 9000 rpm, wont be efficient at lower rpm's.

 

Your asking something to do stuff it can't. The motor the way it is from the factory was not designed to operate vtec all the time. The way our instructors tell us is simply, if the engineers made it that way, they did it for a reason!

 

The engine doesn't need additional airflow at low RPM. It's a small bore 4 cylinder, that doesn't have displacement on it's side to make large amounts of power off idle. Higher air velocities are achieved at lower valve lift at low RPM which maximizes power at low engine speeds.

VTEC is the best of both worlds. A low lift and duration profile is used to maximize low engine speed power, High lift high duration for max power at high engine speed.

Increasing duration is done at high engine speeds because there is less time for the needed air to fill the cylinder.

 

Try to imagine walking up some stairs, the stairs are broken down in two stages, one and two. Stage one stairs are nice and easy and are used to get you to the big stairs (stage two) where the true power is made.
What im getting from your question is, what if you just had stage two stairs all the time?. You would loose power because the motor wouldnt have that easy stage one transition to get to stage two. It would have to struggle to get to the point where it could handle the more air and fuel.

Hope that helped?

 

http://auto.howstuffworks.com/question229.htm

http://auto.howstuffworks.com/framed.htm?p...vtec/index.html

 

Or that ^

 

I appreciate all your replies. Now I have a much better understanding of how VTEC works. Thank you!

 

also, you were thinking of VTEC-E such as what the civic has.