I come from the world of push rod V4 engine and there are lots of parts in the valve train. But, even with an overhead cam engine you have valves, springs, retainers and lifters. As the cam turns all of those elements head "down" and the back "up". Pushing the valve open is parasitic loss (the force never makes it to the crank/wheels). It comes from the force needed to compress the spring and the force needed to push the valve train open (remember things at rest tend to stay at rest)

The job of the spring is the control the valve and bring it back to the seat when the cam lobe rotates away. Choice of a spring should balance the need to control the intertia of the valve train and the minimization of parasitic loss compressing the spring.

Without getting into a bunch of math, we can broadly say that the momemntum of the valve train is 1/2 Mass x Velocity **2 (squared). So more an more force is required as RPM (valve train speed) increases.

So the needed spring pressure is a function of valve train mass and maximum RPM. The sweet spot is involves choosing a spring that provides just the right amount of control, no more and no less. Choosing a spring is more comlicated of course, you must consider seat pressure (closed valve), valve lift (no coil bind), open pressure (this is the one that deals with valvetrain inertia), and harmonics. Double and triple spring setups are used to satisfy these requirements.

But, the cats meow is to lessen the valve train mass. Then you can a) lower the spring pressure or b) rev to higher rpm. For example an OEM V4 retainer weighs 28 grams, custom titanium retainers weigh 8 grams. Similarly the OEM lifter weighs 103 grams, and a bottom ball seat lifter weighs 53 grams. I have no experience with titanium valves (not recomended on cast iron heads) or stainless steel valve.

This is a relatively cheap way to unlock great potential in a T16 (or any) engine.

Chris


posted by 69.50.51...

• Valve Train Interia, Chris Moberg, Wed, 19 Oct 2005 07:05:07 <-- Viewing This Message
  • Re: Valve Train Interia, js, Thu, 20 Oct 2005 15:12:32
    • Re: Valve Train Interia, Chris Moberg, Thu, 20 Oct 2005 16:20:12
  • Re: Valve Train Interia, Gonzalez, Wed, 19 Oct 2005 21:49:52
    • Re: Valve Train Interia, js, Thu, 20 Oct 2005 15:15:23
  • Re: Valve Train Interia, Dean, Wed, 19 Oct 2005 11:15:23
  • Re: Valve Train Interia, pokeyjoe , Wed, 19 Oct 2005 07:34:59
    • Re: Valve Train Interia, Chris Moberg, Wed, 19 Oct 2005 07:59:39
      • Interesting old Mercedes solution..., Chaz, Wed, 19 Oct 2005 13:23:15
        • Pretty sure the desmodromic valve was invented >, Bill Davies, Sun, 23 Oct 2005 06:42:43
        • Ducati Desmo, Drew in Houston, Wed, 19 Oct 2005 15:24:01
          • Cool. NIce to see I was right about Mercedes too..., Chaz, Fri, 21 Oct 2005 03:53:13
          • Re: Ducati Desmo, Lars Tomasson, Wed, 19 Oct 2005 21:53:46

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