does anyone have a formula for calculating spring pressure at different installed heights? i thought I had a formula around here.. but no findy..

for example.. have a 1.960" installed hieght and want to run a 1.880" installed height spring. If its 160 lbs on the seat at 1.880" what would the seat pressure be at 1.960" installed height.

thanks

Traviss,
The first thing you want to consider when choosing a spring (in conjunction with dimension and rate) is the wire quality. Most purveyors now offer endurance springs that are constructed of a super-clean chrome silicon alloy material. I would not consider any other spring. Also there are suppliers outside of the big three (Crane/Comp/Iskenderian) that have made some very significant advancement the development of endurance springs. Endura-Tech alone had 19 wins, 77 top 5s, and 139 top 10s in Winston cup last year, but don’t get the press that the companies with large print ad budgets do in major publications. Hyd-roller lifters have the greatest mass of any lifter and are the most difficult to control at sustained high RPMs, requiring an optimized valve train and spring for reliability. These smaller companies have done some very advanced engineering projects and should not be considered “boutique” by any means, they just aren't supermarket. Same with the cam companies, where you can actually speak to an engineer at Cam Motion/Bullit/LSM for a custom to application cam instead of a shelf item. Get your open/closed figures, spring dimensions, match your retainers, keep it as light as possible on the valve side of the rocker fulcrum, pick the right spring, and keep the geometry correct and you will have a very reliable valve train. Its money saved in the long run. Here are some links to research.
Bob
MarineKinetics
http://www.endura-tech.com/
http://www.eibach.com/evs.htm
http://www.racingsprings.com/products2.htm
http://www.coilspring.com/dragvalve.html
http://www.revvalves.com/

thanks rmbuilder. I am checking all these sites. I am going to be running a solid roller cam with these.


Crane recommends a spring with 145 lbs on the seat and 345 lbs open. In my mind I think this is not enough.

I think a solid roller should be at least 160 lbs on the seat and between 350-450 open.

Right now I have found a spring which is 160 on the seat and 472 open.

Do you think that is too much for a small block spinning 6000+ rpm

Traviss,
You can send me the specs/part#, installed height range, etc. on your Crane I can return some suggested springs. I can either post them as pictures or email them to you. [email protected]

Spring rate is calculated using the following
formula.
K= __open load – closed load___
Installed height – open height
K=Stiffness
(Calculation will be in lbs./in.)
Bob

thanks bob.. sent you a email


Travis

Traviss,
Problem solved! You have email.
Bob

Traviss,
The #99876 spring @ 1.960 is correct for a solid roller running .600” lift. It will net you 170# on the seat and 470# @ 1.360. These springs will not reach fuss point below 8000 rpm and you will be a min of .120 from coil stack.
Important. You can obtain worthwhile reliability and HP increases by changing pushrods. Increased spring rates and lifter acceleration result in difficulties with pushrod deflection and harmonics. Going to a .080” wall thickness/5/16 pushrod will reduce chatter, resulting in increased spring and roller stability and significant HP/reliability +, especially above 5000 rpm. The increased stability on the pushrod side transfers to the spring side as well reducing the tendency to “vault” the valve.
I would suggest that you check your retainers, keepers and spring pockets. If the heads are off I would also check for guide/seat/valve seat concentricity.
When you run the springs for the first time, bring them to full temp running below 2500 rpm, shut down, cool to ambient, and you’re good to go.
Bob

Thanks for the info bob. I appreicate it alot.! I have to buy new pushrods anyway and I see crane has a pro series, on peice pushrod, thats .080" wall for $140. Those will probably be my choice after i figure out which length I am gonna need. I am taking my heads in soon for a valve job, I'l have them look them over for me.

I was going to buy new retainers and keepers, cause in my mind its cheap insurance. In this setup, are titanium retainers worth the money or not.?

traviss

You need 2 parameters to figure the spring curve.

Free length
spring rate
pressure at ht#1
pressure at ht#2

From any 2 of the above parameters you can interpolate the rest of the curve.

Valve springs are wound "straight", not progressive. This means that a spring with a rate of 470#/in will have zero pressure at free length, and at 0.100" compressed it will have 47# of pressure, and at 0.500" compressed it will have 235# of pressure.

So grab you some graph paper and draw a pressure vs length axes. Plot any 2 of the available parameters (or all of them if you have them) and then use a ruler to draw the rate curve (it is called a curve but it is going to show up as very close to a line). From this, you can see your pressure at all heights.

Now, you can do it with math, too.

If you have the pressure at 1.825 (let's say it's 130#)
and the rate (let's say it's 400#/in).
and you want to run at 1.975...

1.975-1.825=0.150

400 x 0.150 = 60

pressure @ 1.975 is 130 - 60 = 70#

*under NO circumstances is it okay to run a valve spring at less than 10% preload * In fact, 15% is a better figure. At less than 10% preload, the bouncing can cause the ends to hammer on the retainer.

thanks for the info mcollinstn. Have found a spring that will fit my installed height. You are just always full of info i like it!

Travis