Assumption: Valve train deflection increases with lift & higher spring load

[BradH]

If you have a valve train that shows 1.55 ratio w/ soft checking spring and 1.50 with actual springs, is it a valid assumption that the valve train deflection increases with lift & higher spring load?

Example: You measure a .05 ratio loss based upon differences in max measured lift due to deflection w/ the actual springs. Would you expect that it might only be .01-.02 ratio loss in the first .100" valve lift and maybe .06-.07 ratio loss in the last .100" valve lift, but with it averaging out to .05 loss overall?

[F-BIRD'88]

Realize that the deflection is dynamic. When the engine is running it is loading and unloading, rebounding on every cycle. What ever energy is put in is either returned or lost as heat. Resonance/vibration also is induced and moves about
"in phase" or out of phase with valve system motion.
Then there is bounce, and and or lofting and its vibration at high speed.

[David Redszus]

Realize that the deflection is dynamic. When the engine is running it is loading and unloading, rebounding on every cycle. What ever energy is put in is either returned or lost as heat. Resonance/vibration also is induced and moves about
"in phase" or out of phase with valve system motion.
Then there is bounce, and and or lofting and its vibration at high speed.

Dynamic is right. Very dynamic.

At 6000 rpm. the valve frequency is 100 Hertz, but the spring coil frequency is typically six times higher.

Valve force depends on acceleration and mass. Depending on camshaft design and engine speed,
when valve forces are highest, spring forces are not.

But resonance disturbs all the nice clean calculations. Pushrods flex and then push back, valves bounce,
springs surge, etc....and the beat goes on.

[BOOT]

Pushrods flex and then push back

Yah but after the load is removed and lift is on the decline right? We're not talking like a slick sidewall storing and returning energy. Peak lift is still lost even if duration is lofted. Not saying if that is good or bad just saying that's how I understand pushrod deflection.

[CamKing]

Yah but after the load is removed and lift is on the decline right? We're not talking like a slick sidewall storing and returning energy. Peak lift is still lost even if duration is lofted. Not saying if that is good or bad just saying that's how I understand pushrod deflection.

Nope.
The pushrods flex, as the lifter accelerates towards max velocity(this reduces the acceleration rate of the valve). After max velocity, the lifter slows down towards max lift. During this negative acceleration, the pushrod starts to straighten back out(this increases the acceleration rate of the valve). This can cause the valve to loft well above the static max lift.

[dannobee]

One of the old tricks in Stock Eliminator was to loft the valve but pay close attention to the retainer to valve guide/seal clearance. That clearance then becomes "max valve lift."

[panic]

The pushrod returning to its nominal length does a pole vault to the rocker & valve.
The return time in seconds is fixed, RPM is completely disconnected. The effect will occur very early at lower RPM, etc. and later with rising RPM.

Some compliance is to be suspected in many VT reciprocating components, but not to the same degree or the same effect.
The original pushrod diameter is almost always not rigid enough, and some rockers have a "kick me" sign painted on the body where the mfg. cut them away for spring/retainer clearance.
So far, no gossip of 7mm stems bending, but...

Saw this somewhere.
Q: "I know the upper half of my valve/spring/retainer should follow the cam mfg.'s design, but what about the bottom half. Is it stable?"
A: "At speed, the bottom coil etc. splashes around in the oil on the head like a sparrow in a bird bath".

[compguy]

Dynamic is right. Very dynamic.

At 6000 rpm. the valve frequency is 100 Hertz, but the spring coil frequency is typically six times higher.

100 Hertz at 6K rpm? or 50 Hertz?

[David Redszus]

Dynamic is right. Very dynamic.

At 6000 rpm. the valve frequency is 100 Hertz, but the spring coil frequency is typically six times higher.

100 Hertz at 6K rpm? or 50 Hertz?

Good catch.
Valve frequency for a four stroke at 6000 rpm is 50 Hz, not 100 Hz.
Piston frequency is twice that of valve frequency.

Since spring natural frequencies are about 500-600 Hz, it would make them twelve times higher at 6000.

[compguy]

Dynamic is right. Very dynamic.

At 6000 rpm. the valve frequency is 100 Hertz, but the spring coil frequency is typically six times higher.

100 Hertz at 6K rpm? or 50 Hertz?

Good catch.
Valve frequency for a four stroke at 6000 rpm is 50 Hz, not 100 Hz.
Piston frequency is twice that of valve frequency.

Since spring natural frequencies are about 500-600 Hz, it would make them twelve times higher at 6000.

Just keeping you honest there David.....!