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Old 01-12-2006, 10:57 PM
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what governs proper installed height?

I am havig a litte trouble figuring this out.

I am using comp cams 986 springs in my 3.8 Ford V6, they have the following specs:

986 Double
OD- 1.400
ID- .697
Seat Load- 132@ 1.750
Open Load- 280@ 1.250
Coil Bind- 1.150
Rate (lb/in)- 296

My machinist called and pretty much said my stock intakce valves weren't long enough to attain the installed height of 1.75. I am using SBC exhaust valves (slightly longer than mine) and they reach the required stock height just fine.

Then I ask a guy I knew to be using the same springs with all stock valves, and he says his machinist used the factory installd height.



So my question, what determines what the installed height should be? I notice the springs advertised seat load is measured at 1.75, so is this what the target installed height is?

I read somewhere that the cam card will show the requied installed height, but I've never seen that on the cam card...

Thanks guys!

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Old 01-12-2006, 11:37 PM
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installed height is the measured distance between the bottom of the valve spring retainer and the spring seat. several things can affect this. these are: valve stem length, shim thickness under the spring (when used), retainers or locks designed for increased installed height, valve seat depth, and spacers under the spring (in certain applications, where applicable, thicker than shims). the spec on the cam card for installed height is the 1.75" spec. this is measured with your valve fully seated, and the retainer and locks installed and firmly pulled up. i use a height mic for this, but there are also calipers designed to make the measurement as well. if you change the installed height, you change the seat pressure of the spring. longer height will usually leave you with less seat pressure, shorter heights will leave you with more. also, if you install springs with less than the recommended installed height, depending on the spring, there is the chance of coil bind before full lift is achieved. there are alot more details to it than this, and i'm sure i've missed some info, but this should give you an idea of what you are looking for. best bet is to use the specs they recommend, and the proper components to achieve those specs.

Last edited by predator carb guru; 01-12-2006 at 11:48 PM.
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Old 01-12-2006, 11:49 PM
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Thanks, so the 1.75 is what I need then?

I mean I don't quite get what the cam card has to do with installed height, other than having enough pressure without coil bind... Unless the term "cam card" is used interchangably with "valvespring card"???

Thanks!
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Old 01-12-2006, 11:52 PM
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the information on the cam card is there so you have the specifications and details about the cam, and what the recommended spring is, as well as recommended specs for installing them. the cam data is used for degreeing in the cam. it is used as a reference so when you degree it in, you can check actual measurements against what the factory says it should be.
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Old 01-13-2006, 12:37 AM
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I understand that, but my cam card don't say anything about installed height that I can find... I have another cam card from my truck that recommends the spring pressure, but it didn't have any reccomendation of installed height.

I got my cam from a distributor that "dissapeared" and all i got was a "cam doctor" profile, and I don't who the actual grinder was...

The main question is do I use the 1.75 seat load for 132lbs figure it gave for the install height...

My machinist seen the cam doctor "cam card" and the spring specs, and indicated that he was aiming for the 1.75 instlled height, but I didn't have much time to discuss it with him, but this is kind of a good opportunity to get the 1.84 SBC valves I really wanted to go with in the first place. But now I am concerned with wether or not this is the correct installed height...

Thanks!
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Old 01-13-2006, 05:34 AM
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Does the cam card you have recommend a particular model spring? Does it recommend a particular seat pressure?

If the springs you have are the springs that are recommended on the cam card then yes 1.75 is the installed height.
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Old 01-13-2006, 05:49 AM
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springs

You are somewhat correct that the cam card really has nothing to do with installed height...

The installed height is determined by the spring manufacturer. when you install a spring it needs a certain amount of load in the installed position. That is where you get the seat pressure from. If the spring is called out to be 1.750" installed and you install it at 1.850" then you might loose 50 lbs of seat pressure, also it would effect the over the nose pressure...So the other end of that is if it's installed at 1.650" then you might have a extra 50 lbs on the seat....I am guessing at the numbers because that is all determined by spring rate. I just used them as a example...

The cam card is used to determine these numbers. You can if you want to take the time ( or your machinist) look through the hundreds of springs and find one that fits your present height requirements and seat and over the nose pressures.... Also you can get offset keepers and retainers to help you get the correct height. Well i am not sure about your engine but they are available for the popular race engines...

Does this help with you understanding of installed height...It's just a number used by the spring manufacturer to let you know what the spring is made to do....

Keith
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Old 01-13-2006, 08:30 AM
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What is your max valve lift? Here are the specs for your springs at various heights:

1.75 132
1.70 147
1.65 162
1.60 176
1.55 191
1.50 206
1.45 221
1.40 236
1.35 250
1.30 265
1.25 280
1.20 295
1.15 310

What type of cam are you running? What is the max installed height you can get to right now?
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Old 01-13-2006, 08:38 AM
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Every spring has a specific rating at a specific installed height. You have to make sure it is physically possible to install your spring in your head at this height first off.

But there are many factors other that I.H. to look for.

You need to know the coil bind height as well.

You need to be able to install the spring then subtract the lift of the valve and see how far away from coil bind it is. I try to keep a .100 safety margin.

So I take coil bind + .100 + valve lift and see if it adds up to LESS than the installed height. If not then something needs to be corrected.

Also the distance from the bottom of the retainer to the top of the valve stem seal or guide has to be at least as much as valve lift. Or it will crash.

Buying the recommended spring for the cam is good to go most of the time.

After working the heads I see where the valve spring is going to set up (install) at. I know what seat pressure I want and I select a spring that way.
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Old 01-13-2006, 10:56 AM
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Quote:
Originally Posted by Infomaniac
So I take coil bind + .100 + valve lift and see if it adds up to LESS than the installed height. If not then something needs to be corrected.
Hmmm so my max cam lift on the exhaust side is .537, so 1.150+.100+.537=1.787... And the installed height the machinist is trying to get is 1.750

So my safety margin is only .063, is this bad???

Last edited by sizemoremk; 01-13-2006 at 11:03 AM.
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Old 01-13-2006, 11:10 AM
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Quote:
Originally Posted by sizemoremk
Hmmm so my max cam lift on the exhaust side is .537, so 1.150+.100+.537=1.787... And the installed height the machinist is trying to get is 1.750

So my safety margin is only .063, is this bad???
according to my CompCams catalog 1.100 is where coil bind occurs on those springs
1.75-.537=1.213 so you'd be .113 away from coil bind
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Old 01-13-2006, 11:41 AM
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Quote:
Originally Posted by engineczar
according to my CompCams catalog 1.100 is where coil bind occurs on those springs
1.75-.537=1.213 so you'd be .113 away from coil bind

Hmm, right here it says 1.150 again...
http://www.compcams.com/catalog/303.html
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Old 01-13-2006, 11:52 AM
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hummmm

My print catalog says 1.100 but it is a year or so old

sounds like a call to CC might be in order
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Old 01-13-2006, 12:06 PM
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.063" is pretty close man. Be working those springs real hard.

I prefer to measure coil bind myself. Very carefully in a bench vise if you dont have a spring tester.
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Old 01-13-2006, 03:53 PM
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Well the comp cams guy said the coil bind spec was 1.150, but he also siad that .063 would be OK.

Now the problem is that he said they don't make a spring cup for these springs, and suggested I just let the springs rest on shims.

I know of a guy that said he put his springs on the shims with this particular head, and it screwed the whole motor up with aluminum shavings etc etc...

I ended up calling my machinist back, and he said that he could surely find a spring cup or seat that would fit these springs, but seemed to think that the a good hardened shim would not have this problem.

I guess i'll ahve to hope that he can find a seat or cup that will work...

Any more input would be appreciated.

Thanks guys!
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