Rev Kit Please Answer Question!

Discussion in 'High Tech Retrofits' started by lluciano77, Jun 25, 2006.

  1. camdoc

    camdoc Veteran Member

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    Jake, on a solid lifter cam, the ramps are typically designed so that all of the initial opening and closings are done at ZERO acceleration when lashed correctly. The most common ramp is a constant velocity ramp. All of the valvetrain members are elastic, and they need to be preloaded before you can apply the high accelerations to the system. If the cam is properly designed, the valve is never in a free fall condition, it's always controlled by the lobe, until you reach limiting speed.
     
  2. Marv D

    Marv D Veteran Member Lifetime Gold Member

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    I think your trying to read too deep into what the hydra-rev kit is all about luciano. Like the post above are saying, the hydra-rev kit's job is to control the LIFTER. The hydraulic roller lifter is the heaviest lifter there is for the SBC. You have all the components for a hydraulic lifter, add the oil it holds, and now add a roller to the bottom. But you STILL have a hydraulic lifter only tolerant of so much spring pressure. If you could NOT use a heavy enough spring to control valve and lifter bounce in a particular cam (because of the hydraulic valving), the hydra-rev kit fills the gap without placing any spring pressure on the pushrod cup or hydraulic valving. I run one on my little 383 with AFR 210 heads. The SSI stainless 2.08 intake valves are pretty heavy by themselves, add the heavy SpeedPro hydraulic roller lifter and she floats at 6300-6400. Doesn't matter, the cam really isnt making any power up there anyways. Very few hydraulic rollersdo. I'm not using it to extend the rpm range of the motor, I'm using it to control the lifter. Lifter bounce is an ugly ugly thing when things finally decide to fall apart.
     
  3. jakeshoe

    jakeshoe Veteran Member Lifetime Gold Member

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    Camdoc,
    At 7000 rpm a valve has to close 1750 times a minute, to close that fast it has to be moving pretty quickly. I understand it is controlled by the cam but to close a valve that many times, the speed has to be fairly great.

    In slow motion everything would be very controlled, but the higher the rpm goes up, no matter how the lobe is designed, it has to set the valve on the seat, the faster you spin the motor, the faster it sets the valve down, no matter how easy the ramps are on the cam.
    That's my simple explanation. Obviously as you stated there's more to it than that but at some point the valve will be hitting the seat pretty hard.

    It amazes me that the stuff holds up as good as it does, and works as well as it does.
     
  4. jakeshoe

    jakeshoe Veteran Member Lifetime Gold Member

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    Also,
    I know solids generally have a ramp to take up lash, however, how can you have ZERO acceleration, and lift the valve.
    Say you have a tight lash profile that requires .0016" lash. Simplified, the cam's take-up ramp would be very gentle for the first probably .0025" lift.
    Then the lobe would begin to accelerate the valve more quickly.

    Once the cam takes up the lash, if it lifts the valve off the seat even .001", that is acceleration. If it had zero acceleration, it would never lift off the seat.

    Maybe you're stating that if the lash is .0016", then the cam takes up .0016", then at .0016, the faster acting portion of the lobe begins?

    My understanding is that there is usually a wider ramp than what the lash is, because on some cams you can vary the lash by quite a bit. Comps Magnum series go from .0018-.0030" IIRC.
     
  5. camdoc

    camdoc Veteran Member

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    Jake, good question! First, remember when you're talking cams, everything is in inches per degree, (in/deg), not inches per second, so you are correct, as the RPM goes up, the velocity (in/deg)*(deg/sec) goes up, and the acceleration goes up as the square of the RPM! Yes, things get hectic in a hurry.

    Now to answer how can you make movement without acceleration? You can't, BUT.........the lifter is travelling at constant velocity as all of the clearance is taken out of the valvetrain, then the valve starts to open. You're correct, the valve accelerates at the instant that all of the clearance is taken up, then it opens slowly for a few more degrees at zero acceleration. Just like coasting on a flat surface in your car, your covering ground at constant velocity, the valve is opening more, just not accelerating. Once the valvetrain is properly preloaded, the high accelerations can be applied.

    Why do this constant velocity opening? The valvetrain clearance changes as a function of RPM, just like you said above, the loads go up, so the deflections do too. You need ramps that are long enough so you don't slide hammer all of the components with high opening and closing accelerations (like putting a mechanical lifter on a hydraulic camshaft and lashing it at 0.030)

    There are other types of ramps, constant acceleration, and constant jerk too, the L82 GM profile used a constant jerk closing, it's a pretty radical design for an OEM cam.
     
  6. jakeshoe

    jakeshoe Veteran Member Lifetime Gold Member

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    camdoc,
    Good answer.
    I understand what you're saying (or think I do).

    We're talking about two different things, you are speaking of the cam ramps and I'm speaking of the valve, as far as acceleration is going.

    What you are saying is the ramps begin the transition but stay at a constant velocity. This constant velocity is maintained until the end of the ramp and then becomes the faster rate of lift of the actual intake valve opening profile.
    The ramp is constant velocity, but at some point it accelerates the valve, which would then be at a constant velocity, until the end of the ramp, and then the valve and the ramp would be accelerating.

    Thanks for the answer.
     
  7. camdoc

    camdoc Veteran Member

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    Yes, we probably didn't help answer the rev-kit question, but covered some interesting ground.

    What are you majoring in Jake?
     
  8. jakeshoe

    jakeshoe Veteran Member Lifetime Gold Member

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    I already have an Associates in Technology, I'm taking courses to get a Bachelor's in Business Management online.
    My employer pays 100% tuition re-imbursement plus I get the GI Bill. I thought two classes would be no problem. It really isn't that bad but it requires more time than I have with all the other stuff I have going on.

    I plan to take some engineering classes later (maybe also get an ME degree) but I will do that at University of North Texas instead of online.

    A dual degree in Business ( and MBA) and engineering (ME or IE) would set me up at my employer.

    I'm making money going to college....lol.
     
  9. lluciano77

    lluciano77 Guest

    I have a BS degree as an electrician. That is, I went to 5 years of school to get my journeyman's certification. So the degree is kind of BS. I can transfer my credits over to college credits, but I think I will stay in this field.

    The automotive field is fun as a hobby, but I wouldn't want to do it for a living. For me it would be kind of like doing this :dumper: where I eat. It would take away all the fun.
     
  10. camdoc

    camdoc Veteran Member

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    Good for you! The combination of a business degree and an engineering degree gets you big dollars in industry. Enjoy the business school part of it, engineering school basically takes away any social life for years. Get the ME degree, you can always go back for an MS in something else if you're not schooled out after the MBA and BSME!

    I teach Mechanical Engineering Technology now, it's more fun to be on this side of the desk!
     

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