What Is VTEC

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What Is VTEC

Post by R13NGY on Fri Nov 09, 2012 7:56 pm

VTEC is Honda's trademarked acronym for "Variable valve Timing and Electronic lift Control"

VTEC is actually a generic name for several different systems within the Honda engine lineup. You have the SOHC VTEC which operates only on the intake valves, the DOHC VTEC which operates on both, and in other countries there is a three stage VTEC system which I believe only comes on DOHC cars (130 hp from 1.5 liters and excellent mileage is the example I'm familiar with).

The principle of all the VTEC systems is the ability to change cam profiles at a given point within the rpm range. This allows a cam which will easily idle and pass emissions for everyday driving, but provides an extra kick on the top end (it can also be used to improve economy or low end torque).

This change in cam profiles is accomplished through the use of a solenoid and oil pressure. At a given rpm, oil pressure is allowed to lock together the normal cam followers and a third follower. This third follower is actuated (normally) by a higher lift and duration cam lobe and is supported be a lost motion assembly. When the followers lock together, the two valves being controlled are following the exact same profile (most DOHC motors have a slightly different profile for each valve to improve swirl and combustion).

The implementation is much more complex in the SOHC system because of the need for a very complex actuator system to get around the limitations of a single cam to actuate 4 valves per cylinder.

The actuation of the system does indeed follow a hysteresis loop and the actuation point is variable based upon load and throttle position. Without the hysteresis loop, you would have a certain point where the system would rapidly cycle in and out, causing problems.

The three stage system actually actuates only one valve at low rpm, both valves at mid rpms and then switches to a high lift lobe on the top end. Sounds complex, but the implementation is actually elegantly simple.

To sum up, there are no additional valves in VTEC systems, just a different cam lobe with which to actuate your valves. The only necessary additional parts are the solenoid, different cams, lost motion assemblies and the ECU to run the system. In general, you won't hear the system activate on a stock car. On DOHC VTEC systems, what most people hear activating is the secondaries on the variable path intake manifold. To take advantage of the system, keep the revs up, hopefully high enough so that when you shift, you won't drop out of the VTEC range. If you had a DOHC car, you'd also want to try and stay in the secondary range of the intake manifold.


If any of this still doesn't make any sense, please check out this link to Honda's website!
http://world.honda.com/automobile-technology/VTEC/#n2

(Was taken from a post on ClubCivic.com. All rights are reserved to the original owner and writter)




R13NGY

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Re: What Is VTEC

Post by Scott94 on Tue Nov 20, 2012 10:42 am

Nice write up there mate
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Scott94

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