Affect of valve spring install height on spring rating..

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Affect of valve spring install height on spring rating..

Post  Mustang-junky on September 7th 2016, 12:16 am

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
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Re: Affect of valve spring install height on spring rating..

Post  bosshoss on September 7th 2016, 1:36 am

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
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Re: Affect of valve spring install height on spring rating..

Post  rmcomprandy on September 7th 2016, 8:54 am

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.

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Re: Affect of valve spring install height on spring rating..

Post  cool40 on September 7th 2016, 9:16 am

Looks like you need a +.050 keeper to stay out of coil bind . Suspect
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Re: Affect of valve spring install height on spring rating..

Post  Scott Foxwell on September 7th 2016, 10:10 am

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.


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Re: Affect of valve spring install height on spring rating..

Post  rmcomprandy on September 7th 2016, 11:27 am

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.

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Re: Affect of valve spring install height on spring rating..

Post  Lem Evans on September 7th 2016, 12:34 pm

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

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Re: Affect of valve spring install height on spring rating..

Post  Mustang-junky on September 7th 2016, 3:05 pm

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
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Re: Affect of valve spring install height on spring rating..

Post  Scott Foxwell on September 7th 2016, 3:18 pm

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.

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Re: Affect of valve spring install height on spring rating..

Post  Scott Foxwell on September 7th 2016, 3:26 pm

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.

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Re: Affect of valve spring install height on spring rating..

Post  Mustang-junky on September 7th 2016, 9:46 pm

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
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