03-23-2011, 09:29 PM | #29 |
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Wait if it doesn't have time to mix intake charge, why would it be better at higher speed, when there is less time to mix?
Hmmm but if it switches to port injection at higher speed, that would limit torque at higher rpm since you no longer have the cooling effect of introducing fuel in the compression stroke, which increases thermodynamic efficiency...and this is supposed to get higher max power right? Or maybe the gains are just from better flow. |
03-23-2011, 09:38 PM | #30 | |
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If everybody just stuck to something more specifically descriptive like 'cam-phasing' (eg: VVT-i) and 'cam profile switching' (eg: VTEC), plus how they operate and which ones (eg: IS300's 2JZGE has 'hydraulic intake cam phasing') I would be a much happier person. ^So what is what on those ones?
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03-23-2011, 09:45 PM | #31 |
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Well I think for Valvetronic, Valvematic, and whatever valvetrain designs that allow phase, lift, and duration control it'd be a huge mouthful, so maybe acronyms and weird names aren't so bad
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03-23-2011, 09:56 PM | #32 | |
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03-23-2011, 10:05 PM | #33 | |
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Variable lift with cam phasing, is how I would describe Toyota's application of Valvematic. There's pretty much only the three mechanisms I can think of. Variable Valve Lift (Valvematic). Cam Phasing (VVT-i) Cam profile switching (VTEC) Most of the named systems like VVTL-i, iVTEC, Valvematic, etc... are just combinations of these. It's just wishful thinking on my part...
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03-23-2011, 10:20 PM | #34 | |
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03-23-2011, 11:18 PM | #35 |
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VVTL is probably the best name for Valvematic and whatever, cuz the way they alter lift also shortens duration. And I think VVTi and VTEC have the same effect, so why not just call them both cam phasing lol.
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03-23-2011, 11:50 PM | #36 | |
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VVT-i alters the cam's position, like you would tuning with cam gears (advance, retard, overlap), on the fly. The ecu has pretty much infinite control of position within the range limit of the system. eg: anywhere within 30 degrees. VTEC changes the cam profile used, as if you were swapping a cam (or two) on the fly. VTEC can change to a pre-set new profile that has more lift, overlap, duration, but it's either one or the other. iVTEC and VVTL-i are basically the same, and do both of the above. Valvematic I'm not super familiar with how it changes to affect the lift part of it, but it is used in conjunction with VVT-i's cam phasing.
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03-23-2011, 11:54 PM | #37 |
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03-24-2011, 12:01 AM | #38 |
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Like a rocker arm that can change it's ratio on the fly, sort of?
What bother's me is that this has been out for a few years in Europe, but why not in North America?
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03-24-2011, 12:38 AM | #39 |
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We are very slow to adapt. Just look at how many people we have on dial up still.
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03-24-2011, 12:39 AM | #40 |
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Has it? I think it's in some particular American models or something, but only a few.
The base model Lotus Elise (which they don't sell in America, because apparently Americans refuse to buy <1.8 liters lol) has an engine with it I think. Probably are some emissions tests that for some reason they haven't done or had trouble passing for some reason, or maybe they're just trying to squeeze more profits out of the American market by getting rid of the old engines here lol. Valvematic should give pretty good fuel efficiency increases I'm guessing because if you look at the rocker thingy if the lift is low, the valve also closes very early, so they have a very low pumping loss strategy of throttling, since reducing lift introduces some restriction, but reduces the air taken in as well. |
03-24-2011, 01:11 AM | #41 | |
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Quadcam ftw. My old Tempo had a swapped Yamaha SHO V8 in it. It was technically DOHC, but they called it Quad-cam cuz that sounded beefier. 32-valve V8s with straight pipes and DOHC are delicious to the aural senses. |
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03-24-2011, 02:38 PM | #42 | ||
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The MPFI systems I've seen tend to have problems with high compression for the midrange RPM like 3-4k RPM where VE is better. DI does allow for higher dynamic compression so that could mean higher static compresion and/or boost . |
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