Purely hypothetical.

So far more questions than any suggestions to answers. Is there a way to calculate how much seat pressure is needed to seal a valve period?

Harmonics, compression, vacuum, weight, valve geometry all seem to be variables. A few of these I'd thought of, but how does it really effect the valves during operation?
 
Are you planning to use some type of electromechanical actuator on the valve to get rid of the cam and associated valve train ?
 
Not entirely what I was thinking to begin with but, either way the questions still remain. Everyone is more curious about my intent with the information than the questions at hand. I have other things that I'm working on, but I need some of this data to begin testing other aspects of designs.
 
The basic design, ignoring all other forces present with an internal combustion engine, can be summed up by examining the basic Schrader valve.

There is a very light spring in there, that probably wouldn't need to be there under the right conditions.

As soon as you add in the attendant forces, the requirements change.
 
The Desmo cam system DOES have Valve springs. It uses a spring around the cam mechanism to keep pressure against the bottom arm in the system that allows it to float up to keep pressure against the top arm.

I'm not demanding anything, but asking for discussion about relative questions.
Is there a way or method to measure seat pressure needed? Or is there a way to go about finding any of the information that I'm asking about?
 
Real time Testing looks like it .
Take whatever configuration your using and half the pressure till it won't operate .
Then slowly increase it .
There maybe such info out there , i sure don't know. It .
Actually it should be a mass over aceleration calculation .
Equal and opposite reaction , you need to stop the acceleration then return it too rest with a similar force .
The stopping may be where the majority of force is involved .
 
Hit and miss use vacum to open the intake valve .
Maximum vaccum available would be 28-29 inches .
Therefore the spring could not be any stronger then available vacum .

How hit-and-miss engines workEdit​

The intake valve on hit-and-miss engines has no actuator; instead, a light spring holds the intake valve closed unless a vacuum in the cylinder draws it open. This vacuum only occurs if the exhaust valve is closed during the piston's down-stroke. When the hit-and-miss engine is operating above its set speed, the governor holds the exhaust valve open, preventing a vacuum in the cylinder and causing the intake valve to remain closed, thus interrupting the Otto cycle firing mechanism. When the engine is operating at or below its set speed, the governor lets the exhaust valve close. On the next down-stroke, a vacuum in the cylinder opens the intake valve and lets the fuel-air mixture enter. This mechanism prevents fuel consumption during the intake stroke of "miss" cycles.
 
Following that train of thought you need just enough valve spring pressure to keep the valve closed when the cylinder is in negative pressure .
 
flattop1 said:
Following that train of thought you need just enough valve spring pressure to keep the valve closed when the cylinder is in negative pressure .
Click to expand...
For your train of thought, how would you deal with the exhaust?
No mention of which valve in the OP. A well designed exhaust system takes advantage of energy already there, in the form of waves.
What happens when a pressure wave arrives at a closed valve with insufficient spring pressure to overcome that wave?
Kinda throws timing out the window.
Thought there should be no discussion of valve float. Apparently assuming float only occurs over the nose of the cam.
Not so, as float is only apparent when evidenced by th valve not sealing, ie bouncing on the seat.

Timing issue again.

The old lofting cams from the flathead days were rpm limited for the class by the seat pressure on the valves.
 
Exhaust wave will require more spring pressure .
Controlling valve float seems to be a key component .
Be it at 800 rpm or 8,000 rpm .
The coil spring appears to be the simplest most effective avenue for valve control .
 
You have a point about the float being over the nose of the cam. I should have specified that float in relation to the cam. Because as you said, anytime the valve isn't sealed when it should be is considered valve float as well.

Now, I did initially consider the exhaust waves but didn't consider the forces to be high enough to overcome even a lighter spring even on a larger engine. Mainly do to compression. I know with most engine setups there is a slight period of overlap where the valves would be unloaded and the cylinder is transitioning to another stroke. I've heard that certain exhaust setups can actually produce a reasonable amount of thrust in a four stroke, but the pulses returning are enough to push fuel back into the cylinder, as long as the valve is open. I suppose it would be pertinent to find that wave threshold.

I know two strokes have some fairly significant pulses, but this is essential to their function and aided by their pipe design. Generally with four strokes this is used in many the same ways but due to pipe design I wasn't aware the pulses were quite as significant. I'll have to do more research in this area.
 
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On exhaust pressure waves, we want to utilize the strongest wave to help evacuate the cylinder, and also start motion /overcome inertia on the intake tract during overlap.

The consequence is a strong wave in the opposite direction as well.

In years past I have been involved in discussions about holes in the exhaust to enhance cylinder filling, especially on restricted engines.

It can be a double edged sword.

Then, there is sound wave tuning vs pressure wave tuning.
 
Much like the FMF power bomb and mega bomb. Essentially one or two holes in the exhaust covered by a shell.
 
Ok, now back to original question.

Even though you do not wish to talk about the cam, it is incredibly integral in determining minimum seat pressure.

How the cam sets the valve on the seat determines minimum pressure. If the valve is dropped from .050 to the seat in a couple of degrees of crank rotation, it's just gonna bounce. Increase rpm, and it slams the seat even harder.
Now we have the spring trying to dampen the bounce, but it rebounds some energy of it's own.

A look at history of GM performance cams from the late sixties will give some clues.
Most were fairly short in duration from .050 to .050.
A cam intended for high rpm had super long duration from seat to seat. This was required because spring technology had not advanced enough to produce consistent performance springs capable of endurance racing.(which was the intent of these high rpm cams.)

Hope this will give some insight into the whys of valve seat pressures.
 
So, to answer the original question, the more gentle you are able to set the valve (especially the intake valve) onto the seat, with little or no harmonics, the less pressure required.

As rpm increases, the time to set valve down decreases, requiring more pressure to control the valve. ( must keep in mind, we are controlling weight of entire valvetrain, from cam face to valve seat, with the valve spring.

Adding ratio rockers to a cam not designed for such, changes the requirements.

The list goes on and on.

I know, I know, you just ask a simple question.

Give me a simple answer.

Lmao
 
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As of right now, it's definitely possible that could be my biggest limitation is being able to determine just how much control I'll have every degree of crank rotation. With an assist on the cam, I believe it will give more control, but that is the point of this endeavor. Find those limitations.

I'm thinking targeting like a stock clone setup, then bump it up in RPM and power and see how it performs on a dyno and push it as far as I can. Not that this is not intended for a stock setup, but I think it will be easier to start there.

This has definitely been enlightening on a few aspects that I hadn't put as much thought towards. I hadn't considered sitting the valve in the seat as you say gentle would decrease spring pressure. But, that does make more sense. Now the question is how to do it gently and still maintain RPM as you said. The higher the RPM the less time you have to sit it down before it has to perform it's next role.
 
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