Request Valve Spring pressure variables

[StreetSleeper]

Ignorance questions to help me understand:

1. Do the valve springs only have to keep the valves shut after the rocker finishes riding the closing ramp of the camshaft lobe onto the heel or base circle of the camshaft? AND be strong enough to resist flutter or vibration/frequency harmonics? Is there any other considerations like installation height regarding spring selection?

2. Why does the exhaust valve pressure have to be the same as intake valve pressure?

When the Typically exhaust valves are smaller, lighter than the larger intake valves.?.

I guess this assumes equal lift.

3. Since lift is usually greater for the exhaust valve is that the reason for the valve spring being the same size?

Is the difference between both valve lifts insignificant? Does it ever become a consideration when racing?

Not sure if it was Yellow Dart but someone said excess spring pressure is a waste and promotes further wear on the camshaft lobe.

4. Is there a lift, verses rpm formula that dictates what spring pressure is required? Or do people usually gauge what springs they need (outside of buying a camshaft package) based on similar cams and experience because of a common practice?

5. I believe that the exhaust valve does have to open against maximum cylinder pressure.
Does this affect spring pressure requirement (or valve spring choice) or is it strictly the lobe lift that determines valve spring selection?

6. Do the aluminum heads have taller/shorter/roughly the same spring height as the iron cylinderheads on SBM? BBM?

7. If someone operated their engine with Rhoads Variable lifters-would that require an increase in valve spring pressure or size to maintain healthy harmonics?

8. What would be needed to ask or research if you wanted to buy say PAC springs for your camshaft if you only bought a camshaft (long ago…)?

Is 901-16 just the generic answer for low performance street cam?

Can you provide any examples for consideration of spring selection for different camshaft levels?


Thanks for any effort to explain my questions!!!

Web definitions:
valve spring flutter: Valve spring flutter is a high-frequency oscillation of the valve disc that occurs when the valve springs are too weak. It can cause serious damage to the engine.

The natural frequency of the valve spring should be at least 13 times the engine's operating frequency. If the spring is too sensitive to a harmonic of the cam profile, flutter can occur.

Fluttering valves behave like damaged valves, allowing gas to slip by when they should be sealing. This can lead to excess heat generation, decreased compressor capacity, and consumed excess engine power. Another symptom is unusual noises from the engine, such as ticking or tapping.

Solutions
To reduce flutter, you can try modifying the design of the spring or cam. You can also use variable stiffness or nested springs to change the frequency of the spring.

__________________________________

valve spring surge?

This surge happens when the engine speeds-up beyond the design limit under certain extreme operating conditions.

Surge typically begins when the valve is fully open. If insufficient spring pressure is present, surge is intensified as the valve closes on the seat.


Thanks a million!!

 

[Jeremiah (jd)]

Camshaft lobe profile, rocker ratio, component weight (valve spring, locks, retainers, valves) and RPM all play a role in picking a valve spring.

Typically valve spring pressure requirements are within a range (i.e 240-260 seat, 720-760 open) that will accomodate both intake and exhaust valves. This works well for engines with a Ti intake and a stainless exhaust valve because the valve weights are closer.

Another factor pertaining to consider is heat. This may be negligable with the spring alloys available to us.

I have a set of early -13 heads with Ti intake and exhaust valves that have different springs on the intake and exhaust valves. These heads were set up by an engine builder with at minimum 1000x morec insight on the subject that I do.

Lastly, a lot of the emphasis on not using too much spring is centered around wear and tear. Another aspect to consider in that equation is spring mass. A heavy tripple 1.625" OD spring might be better for longevity while a lighter 1.550" OD spring with a similar spring rate and IH, etc. might RPM higher due to less mass to control which generally equates to a more stable system. It's not uncommon for a 2.25-2.40" intake valve equipped engine to pick up 3-500 RPM by stabbing in a set of Ti valves.

The 511" in my GTS has 220 closed and 560 open with a .660ish net lift cam. Stainless 2.18/1.81 REV valves, Ti retainers and CM locks. It revs clean to 6800 and doesn't show and signs of the lifter roller wheels skidding. It peaked around 6100 on the dyno so I set the limiter at 6500 hoping for longer maintenance intervals.