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  • Originally posted by Mater View Post
    i thought VVT was a way manufactures can get away from having EGR

    never really paied much attention to the ressons for it. i do know the 3500 and 3900 v6s with the VVT have really flat torque curves
    exactly , on the atlas 6 , the cam phaser is only on the exhaust side , no egr valve

    the 3.5 /3.9 have vvt and active fuel management dod , shuts off cylinders
    Last edited by SpiderGearsMan; November 11, 2011, 07:11 PM.

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    • More thoughts on stiff springs, RPM and VVT

      Originally posted by SuperBuickGuy View Post
      so I'll ask the seemingly obvious question. The whole point of VVT technology is you don't have to spin the motor to the moon to get the same hp (6.2l VVT makes 426 hp, the 6.2l makes 420, yet the VVT motor gets 15% better mileage)... so why do you need higher spring pressures? even if you did, a lighter valve train would accomplish the same result as stiffer springs.... (snicker it would make the cam act smaller.... sorry, couldn't resist.) .
      The real point of a VVT system that doesn't change phasing between intake and exhaust (i.e. merely advances and retards both the intake and exhaust lobes in a fixed relationship to each other) is to alter VE based on load and r.p.m. (better m.p.g. and more torque) and reduce emissions. I'm curious how it would reduce the need to "spin the motor" to get maximum h.p.

      Typically, OEM cams aren't very aggressive. A harder-hitting bumpstick (more lift, more aggressive ramps) often requires stiffer springs to prevent hysteresis. Stiffer springs impart more loads on the cam, which according to anecdotal reports, limits the ability of some VVT actuators to adjust the cam.

      Certainly reductions in valvetrain mass can reduce the need for stiffer springs. But valvetrain mass reductions are fairly expensive.

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      • Originally posted by Stich496 View Post
        sorry nope.. in a pushrod v8 they could add a rev kit.. and wala..
        not with VVT - you have to have more controllable oil pressure to get the cam to phase right again and then you're taking on the mountain of engineering at GM as to what that number is and how to control it. Getting the pressure or volume isn't much of a problem. Controlling it is.
        Flying south, with a flock of bird dogs.

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        • Originally posted by SuperBuickGuy View Post
          the reason I'm interested in it - it allows you to change the exhaust timing to spool up the turbo, or change the intake/exhaust events (they can be changed independently of each other) for incredible mileage capabilities.

          Still pushrod or not, VVT does solve a number of problems that were solved in the past with high lift cams and strong springs.... that's the point I was making about that (said in my best forest gump voice)

          or to put it in the form of a question - why do you need strong springs?
          Valve control at high RPM... I don't think it's the lift that causes problems, I think it's the lobe profile that tosses the valve off the rocker.
          Flying south, with a flock of bird dogs.

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          • Originally posted by Beagle View Post
            not with VVT - you have to have more controllable oil pressure to get the cam to phase right again and then you're taking on the mountain of engineering at GM as to what that number is and how to control it. Getting the pressure or volume isn't much of a problem. Controlling it is.
            one word regulator.. cause over the life of an engine the oil pump will loose psi at rpm points, and controlling that would be a regulator. so..
            wouldn't a rev sytle kit.. design alow for lighter springs, at the same control point.. for better lobes and rpm

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            • Originally posted by Stich496 View Post
              one word regulator.. cause over the life of an engine the oil pump will loose psi at rpm points, and controlling that would be a regulator. so..
              wouldn't a rev sytle kit.. design alow for lighter springs, at the same control point.. for better lobes and rpm
              you know, I'm full of shit on this one. I thought GM was using oil to control it and that would be stupid hard to control. They aren't. It's gear driven.

              Comp is making range limiters for hotter cams and doing the behive spring dance, I've just never really looked into it. Rev kit away!
              Last edited by Beagle; November 12, 2011, 06:26 AM.
              Flying south, with a flock of bird dogs.

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