Here is an Excel Spreadsheet that will calculate the Valve Spring Pressure of any spring when you know the Height and the corresponding Pressure at two points. It will also calculate the maximum lift of your Cam at a particular installed height if you know where Coil Bind is. The factor of safety used for Coil Bind is 0.060” and can be changed if desired.

http://www.boomspeed.com/mc71454/mc71454_spring_rates.xls

Right Click and “Save Target As”

Please Inform me if there any problems with it.

Thanks

graemlins/thumbsup.gif Awesome Tom! It works great for me.

Look for an e-mail from me next week (my spring break) It should have something for you smile.gif

graemlins/thumbsup.gif :cool:

Originally posted by AdamLym:
graemlins/thumbsup.gif Awesome Tom! It works great for me.

Look for an e-mail from me next week (my spring break) It should have something for you smile.gif Thanks Adam....

Works great! Thanks it'll be handy for sure.

ttt

I imagine you're assuming a linear spring rate constant?

Yes,

you have too, There is no other choice. If I could get data for the springs at 3 or more positions then a crude equation could be written, to any more accurate than a linear relationship,4 or more values would be needed.

I m mostly computer illeterate...I save as: but when I go to open it..it asked with what program?...duh...which program do I tell it to use?

Most cam companies have charts that show the spring rates in a column out beside the springs themselves. It's very simple to multiply these times the cam lift and add to the seat pressure to get the total spring pressure your contemplating using. Remember to subtract the lash from the lift total if its a solid lifter or solid roller lifter before multiplying. (cam lift x rocker ratio - valve lash x spring rate + spring seat pressure = total open spring pressure over the nose).

Originally posted by Harold Sutton:
Most cam companies have charts that show the spring rates in a column out beside the springs themselves. It's very simple to multiply these times the cam lift and add to the seat pressure to get the total spring pressure your contemplating using. Remember to subtract the lash from the lift total if its a solid lifter or solid roller lifter before multiplying. (cam lift x rocker ratio - valve lash x spring rate + spring seat pressure = total open spring pressure over the nose). =
HI Harold,
This will give you a close approximation or your spring rate but,,,, always a but huh :D
The spring rate changes depending on the installed height & open height you are using.
In other words, if you take a spring that has a rate of 500 lbs/ inch with a 2" installed height it will have a higher rate if installed at 1.900" going to the same amount of lift.
The inverse of this is also true,
This is not a big deal just something folks should be aware of when pushing the pressure especially on solid lift stuff ;)
You should have your pressures checked at the height you intend to use if it varies much from published specs.

Wolfplace,

That's an interesting take on the difference between pressure and rate. I'm under the impression that the spring rate is determined by the material and wire diameter, while the pressure is determined by the current height of the spring. IOW, I'd say that changing the installed height of a spring changes the seat pressure, but not the rate at which the pressure increases as the spring is compressed.

It could be thought of as a line on a graph, the rate is represented by the slope of the line, while differing heights move the whole line up or down on the graph.

What amazes me is that this is the first time I've disagreed with something you've posted here, and you've posted a lot. smile.gif

Tom

Originally posted by Tom Mobley:
Wolfplace,

That's an interesting take on the difference between pressure and rate. I'm under the impression that the spring rate is determined by the material and wire diameter, while the pressure is determined by the current height of the spring. IOW, I'd say that changing the installed height of a spring changes the seat pressure, but not the rate at which the pressure increases as the spring is compressed.

It could be thought of as a line on a graph, the rate is represented by the slope of the line, while differing heights move the whole line up or down on the graph.

What amazes me is that this is the first time I've disagreed with something you've posted here, and you've posted a lot. smile.gif

Tom Hi Tom,
This was always my understanding also, that spring rate is determined by material & diameter but if you compress the same spring to a different beginning height & compress it from this new height the same amount, call it .600" the apparent rate will change from these two points.
I never gave this a thought but now have the ability to check springs with a computerized load cell & the apparent rate changes with a different starting & ending point as the rate is averaged between these two points.
The rate will be linear but the line will be higher.
If you use the advertised rate & start at a higher point your results will be different given the same amount of lift or movement.
I had to play with a bunch of springs before believing my results & I am not sure I completely understand it yet as you are right, the total graph is linear graemlins/clonk.gif

I m mostly computer illeterate...I save as: but when I go to open it..it asked with what program?...duh...which program do I tell it to use? You need to open it with MS Excel, Although I'm guessing you prob don't have it though, or else it would have opened it on its own...