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Location:
Melbourne
Registered:
November 2003
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Re: VVTi? need info
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Sun, 21 November 2004 02:39
 
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VVT and VVTi both work in the same way. They adjust your cam timing dynamically, just as if you where using adjustable came gears. Obviously, the VVT and VVTi adjust the timing on the fly while the engine is running and not while the engine is off. It does not, however, adjust the cam profile. The different between VVT and VVTi is that VVT has two different cam timings to chose from that switch over at a pre determined RPM. VVTi has a few more, and intelligently switches them based on all sorts of factors.
VTEC works by having not two cam lobes per cylinder, but three. Two of these lobes (the low RPM ones) sit on a rocker that operates the valve. The third lobe sits on a free floating rocker in between the other two lobes. At a certain RPM, a small pin slides from the high RPM rockers to the low RPM rocker while the valve is closed, locking them together as one. The high RPM lobe then lifts the whole rocker (as it's one piece now) off the two low RPM lobes to open the valves for longer and with higher lift. This gives you all the advantages of a large cam profile engine, without the lack of low end performance.
Linkage:
http://www.billzilla.org/vvtvtec.htm
smashed_wombat, what you are talking about is more akin to Toyota's TVIS. At low RPM, a butterfly closes off one of the two ports to increase torque. Above about 4000rpm (is that right guys?) the butterfly opens to improve flow and let the engine rev out. Honda's new economy VTEC works in a similar way. However rather than having a butterfly it uses it's cam profile adjusting technology to stop one of the valves from lifting much at all at low RPM in a similar fashion to what I described above. Both of these only operate on the intake port, not the exhaust port.
There is also a new version of sports VTEC that has 3 stages or something silly like that. While I know it's similar to the other VTEC operation I'm not sure exactly how it works. I think it's kinda a highbred between the old sports VTEC, and the new economy VTEC.
Thank you, that is all. Sorry for the long post.
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| | Subject | Poster | Date |
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VVTi? need info
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device01 | Fri, 19 November 2004 00:49 |
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Re: VVTi? need info
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Nark | Fri, 19 November 2004 01:42 |
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Re: VVTi? need info
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Corona RT142 | Fri, 19 November 2004 02:07 |
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Re: VVTi? need info
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FWDCelica | Fri, 19 November 2004 02:15 |
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Re: VVTi? need info
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wuzah? | Fri, 19 November 2004 08:46 |
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Re: VVTi? need info
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Bill Sherwood | Fri, 19 November 2004 10:56 |
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Re: VVTi? need info
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thu187 | Sat, 20 November 2004 08:01 |
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Re: VVTi? need info
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smashed_wombat | Sat, 20 November 2004 12:57 |
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Re: VVTi? need info
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Nark | Sat, 20 November 2004 22:39 |
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Re: VVTi? need info
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Shraka | Sun, 21 November 2004 02:39 |
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Re: VVTi? need info
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smashed_wombat | Sun, 21 November 2004 02:56 |
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Re: VVTi? need info
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device01 | Tue, 23 November 2004 05:37 |
