• Aug 9, 2009
Honda K20Z3 featuring i-VTEC - click above image to watch the video

The powers that be are pleased you enjoyed the differential video so much. So much so that here's another. Dilemma: you want oodles of torque at low speeds because you must overcome one of Newton's pesky laws about bodies at rest tending to stay at rest. However, once you're at speed you'd like to substitute torque for power. Back in the old days, there wasn't a good solution. In fact, the best you could do was take the big block approach and provide more torque and horserpower than a car's suspension, brakes and driver could handle. There was also the European solution: diesels for torque, fancy-pants DOHC gas engines for power. Or the Japanese method: neither. But what if you wanted both?

Enter variable valve timing. Simply put, without variable valve timing, the valves open and close in a fixed pattern and there's no way to increase or decrease the amount of valve overlap (the percentage of time both intake and exhaust valves are open at once). Depending on the lumpiness of the cam, some engines are good for low-speed torque, some for high-rpm power (and/or valve float). With variable valve timing, the rate and duration of the camshaft striking the rocker arms can be altered, varying the valve overlap and resulting in both better low range torque and better high rpm power. Plus, you get the advantage of increased mileage throughout the power band (if you like). Nifty -- but how's it work? If you'd like to know, make the jump and watch the video.




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  • 24 Comments
      • 5 Years Ago
      Looks good. Maybe we are taking a step back nowadays?
      • 5 Years Ago
      Ah CDX. The auto tech school I go to uses this for extracurricular work.
      • 5 Years Ago
      Cameron, a lot of those blog posts were made by Eric Bryant and he doesn't appear to be around anymore. His posts were generally very good but I think he made the mistake of reading the comments.
      • 5 Years Ago
      I just burped up my hamburg and mac and cheese. Thanks. If I had one tight intake valve it wouldn't have happened. bad timing...this article I mean.
      • 5 Years Ago
      How about a new series on AB? "How stuff wors"?
        • 5 Years Ago
        Along those same lines, what happened to the AB features about actual wrench-turning on "project" vehicles?
        • 5 Years Ago
        Cameron, a lot of those blog posts were made by Eric Bryant and he doesn't appear to be around anymore. His posts were generally very good but I think he made the mistake of reading the comments.
      • 5 Years Ago
      Welcome to 1988, seriously VTEC was available on the CRX that year in Japan. But even if you mean variable lift/duaration AND variable timing. That was standard on some Hondas in 2000. Cool explanation but a little dated.
      • 5 Years Ago
      Some of y'all may be interested in the following, which is another technical one, but it's specifically about Nissan's VVEL and the lack of camshaft in the 370z:

      http://www.370z.com/MagazineArticles/tabid/57/articleType/ArticleView/articleId/14/370Z-Engine-VQ37VHR.aspx

      I thought it was cool anyway. Somewhat related video here:

      http://www.youtube.com/watch?v=lY9L8hoVPRU&eurl=http%3A%2F%2Fwww%2Ethe370z%2Ecom%2Fengine%2Ddrivetrain%2F7173%2Dquestion%2Dabout%2Dvvel%2Dthrottlebody%2Ddrive%2Dwire%2Ehtml&feature=player_embedded

      And yeah - thanks AB for the technical stuff!
        • 5 Years Ago
        I was looking into VVEL the other day... and I like the system, I wanted to know more about it.

        I came across this comparison of BMW's Valvetronic, Nissan's VVEL, and Toyota's Valvematic systems of pro-active variable valve lift.

        Subaru (AVLS) and others have used phase or lobe adjustments to increase valve lift, but like valve timing (AVCS, in subaru's case, VTEC, VVT, etc...), such a valve-lift system is reactive to engine speed, and somewhat on-or-off.

        The BMW, Nissan, and Toyota systems are ECU-controlled, and actually can have an effect on the engine, rather than solely being affected by the engine. Pro-active, rather than re-active.

        I didn't know about the Toyota system before reading about it here, but it certainly seems interesting, and less bulky than the BMW or Nissan systems.

        http://www.autozine.org/technical_school/engine/vvt_5.html
      • 5 Years Ago
      is it me or does the guy sound like an older richard hammond?
        • 5 Years Ago
        +1 for both Paul and BigTeebo!
      • 5 Years Ago
      VTEC uses the cam change variety while most other VVT systems use the cam phasing kind.
      BTW how is Japan neither when Honda popularized the use of variable valve timing in commercial use (i.e. affordable vehicles people actually buy and not high end sports or race cars)? Between Honda and Toyota I would say there's a much higher proportion of cars on Japanese roads with variable valve timing than in Europe or the US.
        • 5 Years Ago
        I think he is referring back to the 70's and 80's.
        • 5 Years Ago
        I am referring to back in the 60s and 70s and a little bit of the 80s.

        For instance, I spent nearly every day in high school in a 1968 Toyota Corona. i.e. neither.
        • 5 Years Ago
        I took it to mean what why not the LS2LS7? said.
        • 5 Years Ago
        He meant Japanese cars had no torque or HP. And he's right. They had very little torque and with the voluntary 280PS limit, the didn't have much power either.

        I wouldn't say cam phasing is more popular than cam shift. It's more complex and expensive and can't vary open duration or amount, which are pretty important for getting the most output (after overlap).
      • 5 Years Ago
      This one was a little harder to follow
      • 5 Years Ago
      That explains how they do VVT on DOHC engines. How does GM do it with their single cam SB engines?
        • 5 Years Ago
        They don't. Dodge introduced it in 2008 with the Viper.

        http://www.sae.org/automag/technewsletter/070402Powertrain/04.htm
        • 5 Years Ago
        While I haven't taken apart my engine and personally looked, from what I've seen/read there is a control module on the cam that changes the phase angle, just like the video explained. It's a continuously phasing system. Since there is only one cam, it phases both intake and exhaust valves, but the downside is that each is phased exactly the same since there's only one cam. You can't control exhaust and intake separately.

        An interesting idea would be to replace the double lobe feature of OHC engines with a variable follower at the end of the pushrod (say, a hydraulic feature that could increase or decrease the amount of fluid in a reservoir in the bottom of the follower) to also vary lift and, assuming you had precise enough control, duration and timing as well. However, given the fact that the whole point of OHV engines is to reduce cost and complexity, it's highly unlikely you'll see anything like that at any point. Your closest hope would be a future LS engine, but I get the feeling those are either close to death or will become smaller and more complex over the next few years.
        • 5 Years Ago
        GM does it on their OHV V6 high value engines since 2004.

        http://en.wikipedia.org/wiki/GM_High_Value_engine

        'These engines (aside from the LX9) are the first cam in block engines to implement Variable Valve Timing, and won the 2006 Breakthrough Award from Popular Mechanics for this innovation.' (ED - the comment about aside from the LX9 is because the LX9 doesn't have VVT, not because the LX9 preceded these engines as the first cam in block engines to implement VVT)

        I don't know how they do it.

        Note this is mentioned in the article you posted about the Viper gaining VVT.
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