traviss

I am trying to understand and find the right spring for a new roller cam in my small block chevy. Crane has recommended two springs.


( 99846) single spring w/ damper

(99838) Dual spring


I am running 99846 springs right now in my motor and when tested it had a max lift of around .580". Crane says it is good for .600, but even on there website it says max gross lift .585.

What I have run into is my new cam has two much lift for the 99846 springs, so i need to use the other spring. So now I am looking at 99838 springs.

theretical lft for 99846 is 1.750 installed hieght - ( 1.100 coil bind + .060 extra clearance) = .590 ( not enough)

theretical lift for 99838 is 1.688 installed hieght - ( .950 coil bind + .060 extra clearance) = .678

I don't know what kinda pressures I should be looking for when looking for a spring.

99846 - seat pressure at I.H = 115# at (1.75") and open pressure and hieght = 350# at (1.175")

99838- seat pressure at I.H = 110# at (1.688") and open pressure and height = 320#at (1.208")


I notice the double spring has less pressure then the 99846 spring. Should I be running a spring with more pressure? because this new cam has more duration, lift ect.

new cam is 234/242 dur. .575/.595 lift on a 112 lsa redline rpm is 5500 rpm

Please enlighten me on this subject guy's


Thanks

Travis

Mr Gadgets

Travis,
Who made the new cam? That is who I would get spring recommendations from. If they are not available then you should take a look at the cam lobe profile and determine acceleration rate of opening, compare this to a similar cam. That may put you in the ball park.
Is this cam a solid roller? or hydraulic? You could talk to all of the cam manufatures and see what they have in a cam with similar specs and see what spring pressures they recommend, then you could decide on a ball park figure.
Usually more lift and duration calls for more spring psi, but I am no expert. I always go by the cam manufacture's recommendations..

Good luck

Dick

traviss

The new cam is a Crane powermax hydraulic roller cam. Those two springs were recommended by crane. Its just I can't use 99846 cause it does not supply enough lift. and 99838 I was unsure off cuase the pressures were a little lower. I see your point Dick, I'll look into some info to give me a ball park figure.. I remember "bruce" on the board telling me to stay around 115# on the seat and around 350# open.. But that was with the older cam. I need new info for this new cam..


Thanks bro

Travis

traviss

ttt

Mr Gadgets

Another thing to do is call Crane back and tell them you are going into coil bind with the single spring. They should have a few more available.. And ask them about pressures at seat and max lift. If not look at other manufactures for the right one.
Good luck

Dick

traviss

Good evening Dick..

I talked to crane a few minutes ago. I told them my situation, and he was still trying to tell me that the 99846 spring could take my lift.. yes it can.. but its very close. As soon as I said the word "boat" he said go with the double spring cause I could get back to the dock if a spring broke.. Weird theory i think He told me to go with the double spring 99838. I calculated out the numbers and this spring can take around .678 lift theretically... so I am set.. I have the part numbers for what i need.. and I asked him if the pressures were correct and good for my application, he agreed that the pressures were perfect..


Thanks for the help Dick


Travis

mcollinstn

Okay, stick with me here... Valvesprings are STRAIGHT-RATE springs (as are most springs). This means that the spring will deflect "x" amount with "y" load, and it will deflect "2x" amount with "2y" load. This deflection is represented by the "spring rate". Take note that suspension springs are sometimes wound with differing numbers of coils per inch which makes them "progressive rate" springs but they do not apply in the context of valvesprings.

Your two springs do have the specs you mention. If we are using a .590 lift cam, then we end up with these spring pressures:

846 spring: 1.75"/115# (no lift)
1.16"/356# (.590 lift)

838 spring: 1.688"/110# (no lift)
1.098"/368# (.590 lift)

** you gotta do some math on the numbers to see your "endresult" pressures for the cam you intend to run.

The math is as simple as this:
Start with the recommended installed height and pressure. If you want a little more or less installed pressure, you can use the spring rate to see where the spring would need to be to give your pressure - remember that you don't want to vary the installed height much in the plus direction..
If you have a spring rate of 440#/inch, then if you have an installed height of 1.900 @ 110#, then an installed height of 1.800 would be (440 x 0.100 = 44# difference: now add the difference to the original installed pressure 44# + 110# = 154#).

Same thing on the other end. They give a ballpark open pressure, but you need to adjust it to see what you really got.

M