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!!

 

[Bewy]

I will answer in just general terms:
- valve float usually happens with the intake valve first because it is [a] heavier not opening against the compressed gas in the chamber which aids the spring in valve train control.
- most experts agree that you should have minimal gap between springs at max lift because the smaller the gap, the less movement there can be to help contain flutter.
- the aggressiveness of the lobe itself is an important factor in determining the springs to use. A stronger spring would be needed with an aggressive lobe.

 

[Newbomb Turk]

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?

Installed height matters. The spring MUST control the valve off the seat, over the nose, down the closing side and on to the seat.

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.

Because the weight difference isn't enough to buy two sets of springs to reduce the spring load on the exhaust.

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.

If you mean size of the spring and rate then the answer is no. You can't determine if the spring load is excessive until you determine what lifter you are using. With any flat tappet lifter you are severely limited in how much spring load you can use. If it's a solid roller then it's hard to get the spring load too high in most cases.

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?

Never seen any math on that. Lift is a consideration only because the higher you lift the valve the higher the open pressure. Again, with flat tappet lifters on common cast iron cores you can be about as high as 160 on the seat and 400 over the nose. And that's pushing it.

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?

The exhaust valve does not open at max cylinder pressure. That would be wasting power and chances are you'd be bending pushrods and breaking rocker arms if you did. Exhaust valve opening is the second most important event next to intake valve closing.

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

Every aluminum head I've seen has a higher installed height than factory cast iron heads.

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?

I'm not sure that that lifter requires anything different from any other hydraulic lifter concerning spring loads. I've never been a fan of them. Buying the correct cam is a far better option than buying the wrong cam and crutching it with those lifters.

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?

Spring rates and loads are dictated by the type of lifter, valve train mass and RPM. Then you have to figure in installed height, coil bind and will the spring fit the head without modifications or if the heads need to be modified to fit them.

A hydraulic cam up to 5000 rpm needs 100 on the seat and whatever you can get over the nose depending on lift.

A hydraulic cam up to say 6500 and I don't let them out at less than 130 on the seat.

If you want more than 6500 rpm you need to run a solid.

A small solid can hydraulic numbers above.

If it's a performance solid it gets 140 on the seat and as close to 340 over the nose as you can get. I've run as much as 180 on the seat with a solid but never on a street car.

A solid roller, even a street solid roller gets no less than 240 on the seat and whatever I can get over the nose.

A hydraulic roller gets 160-180 on the seat but 180 is tricky. That's why I use solid lifters on HR lobes.


t

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!!

 

[RustyRatRod]