Affect of valve spring install height on spring rating..

I just ordered some valve springs for my 545. Cam calls for 160-170# on the seat and 440# open.

My installed height is 2.020".

Springs I ordered are 171# at 1.950" and 482# at 1.300". Spring rate is 494#.

My cam has about .650" lift, so I would be basically adding .070" height to both the closed and open heights.

Is there a formula to figure out how much rate will be lost when increasing the installed height? Thanks.

Jess

you also need to pay some attention to the coil bind number. but basically as a rule the spring rate will not change much so the .070 would run around 35 lbs give or take...

Why not just shim the spring or install a different set of keepers???

dkp

The spring rate is "per inch" so .100" difference in spring height would add or subtract 1/10 of that amount; do the math from there.

Looks like you need a +.050 keeper to stay out of coil bind .

Take your net lift @ the valve, add .050", then add the coil bind height of the spring (say for example it's 1.15") and that would give you your "ideal" installed height.
Example: you have .650 lift, add .05= .700", add 1.15" (coil bind) = 1.85 would be your ideal installed height. I like to get springs installed at < .100" from coil bind as a max. I also check coil bind in the vise with a retainer installed. It's usually less than the advertized CB.

Scott Foxwell wrote:Take your net lift @ the valve, add .050", then add the coil bind height of the spring (say for example it's 1.15") and that would give you your "ideal" installed height.
Example: you have .650 lift, add .05= .700", add 1.15" (coil bind) = 1.85 would be your ideal installed height. I like to get springs installed at < .100" from coil bind as a max. I also check coil bind in the vise with a retainer installed. It's usually less than the advertized CB.

The biggest issue there, is that I have readily seen .020" difference in the coil bind height within the same set of valve springs; you really need to check them all when getting under .090" from bind.

Yep, the published coil bind ht. is not always the same as what it checks in the field.

bosshoss wrote:you also need to pay some attention to the coil bind number. but basically as a rule the spring rate will not change much so the .070 would run around 35 lbs give or take...

Why not just shim the spring or install a different set of keepers???

dkp

Thanks. I was actually looking to loose a little spring pressure, so the added height is fine with me. Motor will peak around 5800rpm and I am using Titanium retainers(already had them), so I think I'll be okay. Unless Someone tells me otherwise. I just wanted to know about where I'd be with these springs.

I'll try Randy's formula too.

Jess

rmcomprandy wrote:

Scott Foxwell wrote:Take your net lift @ the valve, add .050", then add the coil bind height of the spring (say for example it's 1.15") and that would give you your "ideal" installed height.
Example: you have .650 lift, add .05= .700", add 1.15" (coil bind) = 1.85 would be your ideal installed height. I like to get springs installed at < .100" from coil bind as a max. I also check coil bind in the vise with a retainer installed. It's usually less than the advertized CB.

The biggest issue there, is that I have readily seen .020" difference in the coil bind height within the same set of valve springs; you really need to check them all when getting under .090" from bind.

Yeah, that's why I like to check. I should have been more clear and said to use the "advertized" coil bind height, then add .05. That will still usually get you < .100" to CB.

Mustang-junky wrote:

bosshoss wrote:you also need to pay some attention to the coil bind number. but basically as a rule the spring rate will not change much so the .070 would run around 35 lbs give or take...

Why not just shim the spring or install a different set of keepers???

dkp

Thanks.  I was actually looking to loose a little spring pressure, so the added height is fine with me.  Motor will peak around 5800rpm and I am using Titanium retainers(already had them), so I think I'll be okay.  Unless Someone tells me otherwise.  I just wanted to know about where I'd be with these springs.

I'll try Randy's formula too.

Jess

Your rate is 494. Just multiply that times the amount of change to get the change in pressure. Lets say you add a .06 shim. 494 x .06 = 29.64. You just increased your pressure by 29.64 lbs.

Scott Foxwell wrote:

Mustang-junky wrote:

bosshoss wrote:you also need to pay some attention to the coil bind number. but basically as a rule the spring rate will not change much so the .070 would run around 35 lbs give or take...

Why not just shim the spring or install a different set of keepers???

dkp

Thanks.  I was actually looking to loose a little spring pressure, so the added height is fine with me.  Motor will peak around 5800rpm and I am using Titanium retainers(already had them), so I think I'll be okay.  Unless Someone tells me otherwise.  I just wanted to know about where I'd be with these springs.

I'll try Randy's formula too.

Jess

Your rate is 494. Just multiply that times the amount of change to get the change in pressure. Lets say you add a .06 shim. 494 x .06 = 29.64. You just increased your pressure by 29.64 lbs.

Okay. Got it. Looks like I may shim a bit. Thanks.

Jess