Thread: Vvt
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Old 08-19-2011, 09:05 AM   #1 (permalink)
Arragonis
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Vvt

I'm trying to get a handle on how VVT actually works - basically so I can work out how to exploit any advantages it seems to have - and also try and work out what exactly the version George has.

As I understand it the VVT system allows the timing of the valve opening to be varied. Conventional cam timing is a compromise between driveability at low speeds and top end power so this VVT system allows the best of both worlds. The variation in early versions was based on engine speed and later based on throttle opening as well. Also it allows the valves to remain open after they should close - e.g. the exhausts staying open for part of the induction stroke (for EGR) and the inlets for part of the compression stroke to reduce pumping losses.

I came across this which has a comparison of the first system against the Honda VTEC versions. Plus of course there is the entry in Wikipedia which contains some details.

George's engine is the 1KR FE unit. The link referring to VVT-i from here goes to the VVT-i link in Wikipedia, but I'm not sure which version it should be - is it VVT on both sides, or just the inlet side. I assume it is the later version based on throttle position.

I'l like to know more and wondered if anyone had any other details ? I'd really like a BSFC map (wouldn't we all for all of our cars ) but I can only find ones for 4 cyl VVTs.

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