From Steve in NC:Dwell time = 2 x hammer momentum / closing force. Lift = hammer kinetic energy / closing force. Note that, in both eqn's, the relevant numbers for energy and momentum relate to what's left of the hammer's original velocity, after the work has been done that's required to lift the valve head off the seat (i.e., "crack" the valve) against the force of static pressure multiplied by the elasticity (i.e., "give") of the stem and seat.
Red line is double the Mass, original Velocity.... Doubles the Energy and Momentum.... Doubles the Lift and Dwell.... 4 times the area under the curve....
I'm seeing something around 1.5 grams hammer weight per grain of bullet weight?.... assuming you want to drive them in the 950 fps range
If the energy is too high, not only do we open the valve further than necessary, we have the potential to store more energy in the valve spring and poppet position.... and that energy is more likely to be transmitted back into the hammer to produce a greater chance of harmful bounce.... Is that an argument for minimum energy and maximum momentum?.... If so, that would favour heavy hammers moving slowly.... If I understand correctly, increased lift means more energy stored to be returned to the hammer, right?.... Even with beginning to understand how energy and momentum have different effects.... my brain still hurts when it comes to hammer bounce....
Intersting stuff - I'd been thinking similar about the energy/lift, momentum/dwell relationships.Quote from: rsterne on June 22, 2013, 02:07:27 PMIf the energy is too high, not only do we open the valve further than necessary, we have the potential to store more energy in the valve spring and poppet position.... and that energy is more likely to be transmitted back into the hammer to produce a greater chance of harmful bounce.... Is that an argument for minimum energy and maximum momentum?.... If so, that would favour heavy hammers moving slowly.... If I understand correctly, increased lift means more energy stored to be returned to the hammer, right?.... Even with beginning to understand how energy and momentum have different effects.... my brain still hurts when it comes to hammer bounce.... I'd reached the same conclusion about "wasted" striker energy and valve lift and think similar about the bounce issue. I definitely think there's a case for maximising momentum while minimising energy - presumably to (or just above) a cutoff point where increasing the valve lift no longer has any effect on flow because it's choked by the throat or transfer port restriction. I think the key to doing this would be to short-stroke the striker and increase it's mass to get the appropriate momentum; this way you're not increasing the lock time (according to my calcs this configuration should decrease lock time so is a win/win situation). Optimising the striker characteristics in this way should reduce the effects of striker bounce, since during successive instances of bounce the valve will sooner reach the point where lift begins to limit flow; and will hence waste less air..