Purely hypothetical.

ABR #69

ABR #69

Member
What is the absolute lowest seat pressure you'd need to seal a valve while the engine is running without having to follow the cam profile, so I'm talking absolute minimum. Valve float is not an issue to be discussed, period. But, still assuming the engine is running normally in it's normal operating RPM ranges. This goes for any race engine, from Clones to UAS.

Does RPM effect the pressure needed? Remember, not following cam profile, so valve float doesn't matter.

Does compression help seal the valves, or will it counteract and potentially lift the valves open due to harmonics if the valve doesn't have enough seat pressure?

Does Valve diameter change the pressure needed? More, or less depending on the size?

I'm sure I'll add more questions before I'm done, discuss!
 
Poppet valve engines may have that figured out .
Reed valves require very little and use pressure differential to help seal .
I assume your asking about standard intake and exhaust valves .
Off hand I would say ohv would require more then flatheads .
I agree with combative hodaka enough so that cylinder negative pressure
Didn't open them .
Hair pin or clock springs might provide the best closing for the least pressure .
 
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Yeah, I guess I should have specified that it was a tradition 4 stroke valve type setup, but I assumed mentioning the cam and valve float would have lent that idea. Two strokes wouldn't really apply here.
 
A broken spring is immediately apparent .
Not considering valve float and With out considering , following the valve train , a low rpm , low power engine is all I would expect for results .
 
Gotta think beyond cams and valve train. I'm not concerned with that. I want seat pressures and possible issues that would arise with too little seat pressure.
 
Well that clarify's the hypothetical question somewhat .
Affix a mechanical device to positively open and close the valve .
No spring required .

Too little seat pressure would result in incomplete valve seal .
Do too vibration , harmonics and turbulence in the combustion chamber .
 
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Not that simple, still needs a spring. The question is how much? If a XX# spring is normally used, what could you get away with without needing it to follow the cam?

Where can you get off the rollercoaster of "This is what's needed to control valve float at this RPM." I just want to know how much seat pressure is require for the engine to function, and seal if it didn't rely on having the mechanical connection to the cam. Could you cut the spring pressure in half? Does it need to be a quarter, could it be as little as five pound springs on a high revving engine if the valve float wasn't an issue?
 
I have an engine that doesn't have an intake to mount a carb or injector...only has an exhaust port in the cylinder. But it's far from a budget build.
 
The weight of the valve is a consideration.

How much spring pressure is necessary to overcome the harmonics in the spring itself?
Harmonics can cause the valve to open several times after the cam profile has ceased to affect the valve.

Just some food for thought.
 
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