Originally posted by Tom
i have i-VTEC , its alittle more advanced:
i-VTEC system. Variable valve lift is accomplished by using two rocker arms and different camshaft profiles to change the opening of the valve. The other technology is a computer controlled variable camshaft actuator that can vary a camshaft up to 50 degrees relative to crankshaft angle. Let's look at each in a little more detail.
Varying the camshaft in relation to the crankshaft is done with engine oil pressure acting on an actuator located on the end of the intake camshaft. The computer varies the oil pressure to change the rotation of the camshaft on its drive sprocket. This changes the valve overlap. Valve overlap is the amount of time both the intake and exhaust valves are open at the same time. Retarding the camshaft decreases the amount of overlap, while advancing the camshaft increases overlap.
Valve overlap plays an important part in engine operating characteristics. Very little overlap gives the engine a smooth idle and good slow speed torque, but it hinders high rpm engine performance. A large amount of overlap allows excellent engine breathing at high rpm but causes a rough idle and poor performance at low rpm. By varying the camshaft rotation and amount of overlap, the engine can have excellent performance at both low and high speeds.
Variable valve lift is accomplished by opening the valves with two different rocker arms and camshaft lobes. In the past, Honda operated VTEC engines with three rocker arms: two to open the two intake valves and a third that could be locked to the other two causing them to follow a different camshaft profile. With the new "two rocker" design, only one valve is opened at lower engine speeds. This causes the intake air fuel mixture to swirl, optimizing combustion at lower engine speeds. At a rpm programmed into the engine computer, oil pressure is used to lock the two rocker arms together. Now both valves open together but follow the higher camshaft profile the second rocker arm follows
Increased performance is one advantage of the i-VTEC system. The torque curve is "flatter" and does not exhibit any dips in torque that previous VTEC engines had without variable camshaft timing. Horsepower output is up, but so is fuel economy. Optimizing combustion with high swirl induction makes these engines even more efficient.
Finally, one unnoticed but major advantage of i-VTEC is the reduction in engine emissions. High swirl intake and better combustion allows more precise air-fuel ratio control. This results in substantially reduced emissions
blah blah blah its better
THAT'S what I was looking for... someone to break it down for me.
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