Lets talk Valve Spring Mathematics
 

So this is how I understand how to pick out and properly set up valve springs for a cam. Please help me out where I'm wrong. I'm just trying to get a basic understanding on how to keep away from valve float and keeping the valvetrain stable. I will use my cam/valvespring combo as an example. I'm running PRC .650" double springs with a 231/239 .598" .610" cam.

Valve spring specs:
Install Height: 1.810"
Closed Spring Pressure: 144 lb. @ 1.810" Installed Height
Open Spring Pressure: 402 lb. @ .600" lift
Open Spring Pressure: 425 lb. @ .650" lift
Maximum Spring Lift: .650"
Coil Bind 1.080"
Spring Rate: 469lbs/in

First thing is to find the allowable operating range of the spring: (1.810" Installed Height) - (1.080" Coil Bind) = 0.730"

Now find the distance left before you hit coil bind based on camshaft lift: (0.730") - (0.610" Cam Lift) = 0.120"

From here I've read that there should be a 0.050" tolerance or safety net before coil bind..? (0.120") - (0.050" safety net) = 0.070"


So from the math above, it looks like my springs need to be shimmed 0.070" to be in there prime operating range. That should keep the valve train a bit more stable and keep valve float away. Where did I go wrong and what needs to be fixed? :popcorn:

If you don't need the extra seat pressure, there is no reason to shim them. It just adds drag and wear and tear to the moving parts. The extra room left on the lift before coil bind won't hurt a thing and just gives you room to go to 1.8 rockers or a bigger cam without changing springs.

How do you know how much seat pressure you need? Is it based on what the manufacturer of that particular spring recommends?

It's usually dictated by the cam manufacturer based on RPM range and lobe design. Too much valve spring pressure collapses the lifter, beats the valve seats up and creates drag that robs power. Most cam companies only want you to use enough pressure to control the valve, there's no need for more. If you are getting some valve float issues, it will be apparent while tuning it. Then and only then would I try adding any more pressure.

That makes sense! Thanks for your replies man

There is an explicit method of calculating required seat pressure, but it is fairly complex and would need the exact cam lobe profile to get a good answer. White is correct though, if your valves aren't floating I wouldnt worry at all.

Yea I'm not looking to make any changes to my set up. Just trying to understand the process and reasoning behind proper valve train set up and valve springs. I'd be interested in seeing that method smokeshow if there is a link in explaining it.

These two vids are good to watch if you can stand the 8 year old camera kid. Seems like he is hopping on one leg while filming. I wish I had access to a spring pressure tester like that.

How To Setting Valve Spring Pressure 1 of 2 Race Application - YouTube

Is there a website that has that proper work he had during the vid?

Sounded like he had that available for the public but he never gave a website or anything...:shrug: