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Re: Actually.... (archive)

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Posted by Matt on October 24, 2000 at 14:40:09:

In Reply to: Actually.... posted by Mel - Seattle on October 24, 2000 at 14:05:05:

You're correct, VTEC does have a "separate" set of cams that "flip" at a set RPM (approx. 4800 for my 3.2l engine).

If I remember correctly, VTEC engines have separate set of cams which work on or off depending of the rpm's. I could be wrong, not all that familiar with Hondas, I do know that is how Toyota has their "variable" timing engine, known as VVT-i. Basically there is a cam for low rpms and then there is a one for high rpms. The reasoning is that when you have engine that revs up to 9,000 rpms it is hard to have efficient operation at both spectrums of engine speeds, this due to fixed cam profile.

A truly variable valve timing, like VANOS, is a single cam whose profile can varied throughout the all engine speeds. It is a lot more expensive and complex system than VTEC, but it is more efficinet.

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