I noticed that there are single springs that have as much, or more, seat and open pressures, at the same installed and open heights, as dual springs.

What are the advantages and disadvantages of each?

Under what conditions would one be better than the other given the same seat and open pressure?

Thanks,

Pat,
This will be a short answer, because it's late and I have to get up in 5 hours......
Duals are always preferable, at least to me.
Cam curves, and the equations that generated them, have all these exponents of X in them, and each different exponent causes a number of harmonics in the spring. These harmonics are a product of exponent and RPM. At some particular RPM these harmonics cause spring surge , which causes the spring to jump and 'dance'. This is why all springs have dampeners of one sort or another, and why dual springs have different coil windings and direction of winding. This causes the inner and outer spring to surge at different RPMs, and therefore is inherently safer.
Single springs are cheaper, and maintain a stock look, which is necessary for some types of racing.
Obviously, pressure is pressure, and to equal a double spring's pressure, a single spring must be more highly stressed.
I hope this answers your questions, if not, let me know and I'll give it another try....

UDHarold

oops :D

HI Pat,

My opinion is there is really no instance where a single spring would be better except for cost savings.

With the exception in some cases where you can use a progressively wound spring or the so called "beehive" spring which is also a type of progressive spring & is supposed to be very effecient at dampening itself.

My understanding of normally wound springs is a good dual spring will normally be more efficient or stable as the resonate or natural frequencies of two different sized wires will not be the same which should tend to reduce spring surge.
A damper also helps to keep a single (or double) spring from going nuts as does two springs with an interference fit but this creates more heat due to friction between the two.

I suppose you are also taking some of the load off of each spring with two so you are not stressing them quite as much.


========EDIT==============

I see the cam master has already answered,,, guess I type to slow :D

Hi Harold graemlins/waving.gif

Got it. I see what you are talking about. Duals control spring surge much better than a single and spreading the load to two springs reduces the stress on either one. Makes sense. Thanks,

Also better Heat Dissipation - dual springs have more surface area for the oil to cool the spring assembly.

If one spring fails.....

And for braking-in the cam lobes/lifters with only one spring on, and then putting the inners in.

I have a real great opinion of single springs so much so that when I built the 4000rpm 390 Ford for my old truck I made the machinest find a set of double springs that would work. The heavy single springs have a real bad habit of breaking.