comp 980 springs and shimming

[xracerx13]

I am getting ready to do valve springs and am going with the 980's. Engine internals are all stock.
I had them tested on a spring tester for pressure and they all suck at 1.727" installed height because COMP calls for a 1.7" installed height. Obviously there needs to be a shim to make up the space.....
With the addition of a .030 shim under the spring they do hit about 90 pounds on a spring tester.
So my question is for anyone who has done these on a stock head what shims did you use to get your correct install height of 1.727 using the height checker tool?

[Steve Wood]

Joe, that sounds about right as I recall (which I really don't lol)   We always shimmed them to get around 90 psi.  these days, I have changed my mind and get some springs rated around 105 or even a bit more.

[xracerx13]

Ok, but the 105# springs... are they with not using shims? and which exact springs(part number ) are you talking about Steve.
Better question which springs can be installed by themselves at 1.727" without shims that can give me around 90# seat?

[Steve Wood]

Originally, the 979 was suggested if you used the spring cups and 980 if not.  At the same time, there was a chevrolet lt1 spring suggested that went on 350's.  It was rated I think at 105 at 1.70 as I recall.  I suspect most people installed them without checking pressures and the actual pressure was lower at 1.727 than the 105.  These springs held up better under boost over 5000 rpm.  I used to think they were too strong for our weak lobe on 3E but people continue to use them and some are using springs more like 125 psi when closed with good results.

Later, people started finding that cc980s were somewhat erratic in pressures.  I think most installed them at 1.727" or whatever heights the stock head/valves measure.  I would use 1.700" if I used them.

But, today, I would use either the comp 981's that are rated at 105 at 1.700 and would be a bit less at 1.727.    the spring rate on them is 373 so you can figure out what they would be at 1.727 if you wish.  Or I would use the ones Kirban sells that are rated at 100 psi and I think that is at 1.727.  The spring rate is 430 according to Kirban (NOTE, his site says maximum lift is 430 so I am just guessing that is rate but I don't know) so they would be a bit stiffer than the 981s when on the nose of the lobe.  Kirbans are probably a replacement for the LT1's.  The early LT1's that were on the 350.

There are a couple of jillion sealed power springs, pioneer etc that are similar if you look at the specs.

[xracerx13]

I was told by Comp cams that the 981's at 1.75 is 87lbs and we know its 105 pounds at 1.7 install height. So with that info......
I came up with ruffly 96 pounds at 1.727. Not real world spring tester data just common mathematical.

I am a little torn on shimming the 980's and was thinking what to put in, that when installed at 1.727,  gives me close to 90 pounds with a rate closer to the 980's 305 pound rate spec. The 981's are a heavier spring and their rate is 373.

[Steve Wood]

I would prefer 981's

Fortunately, you are old enuf to know how to compute pressures....L OL

[xracerx13]

Ok but 981's without shims to 1.727 to get the 96 pounds?
Or
With shims to 1.70 to get 105 pounds
Remember this is the stock cam

[Steve Wood]

I did not calculate the spring rate but this is what TA Performance sells for stock heads

Product ID: TA_V1436 Stock Valve Spring, V6 Production Iron Cylinder Head	Details
Ideal spring for most street strip 225-231-252 V6 applications. O.D.          1.260 110 lbs  @ 1.727 280 lbs  @ 1.227 Coil Bind    1.115

[xracerx13]

I am not running 110 at 1.727  and wiping a lobe

[xracerx13]

Since the stock installed height minus the cup is 1.727", do you see a problem with me just throwing some .030 shims under the 980's to bring the installed height to 1.697?

I already have the springs tested for pressure and found my magic 12 out of 16 that I want to use and they are within 2-3 lbs of each other. so with an .030 shim I should get around 90 lbs.

OR

Should I just throw a .015 shim in and get 1.712 and around 87 lbs?

[Steve Wood]

Should be fine with the 30s

[xracerx13]

I'm gonna go buy one Sealed Power VS739R from napa today for $6 and see what I get for poundage at 1.727 on a spring tester. They are rated at 104 lbs at 1.7" so Should be around 95 - 96 lbs at 1.727"..
If that's the case I might just go with them and return these 980's. Figure after they are settled in they might drop to 92 lbs.
I keep reading bad things about the 980's and this way I don't have to shim the VS739R''s.
The turbo buick guy thats gonna install them for me usually uses K motion K700's on stock cams and they end up around 108-110 seat pounds at 1.727. I thought that was a little much.
Yes i'm a little paranoid about doing them myself.

[Steve Wood]

Over the years, I have changed my opinion which used to be that stronger springs are not needed and might wear out the cam lobe.    Time has changed my mind LOL

Sounds to me like your guy knows what he is talking about.  K Motion what the GSCA used to sell as I recall.  A few jillion of them were sold, I suspect.  

[ULYCYC]

Your cam and lifters are well married at this point in time.  I doubt any minimal change in spring pressure either way would effect the cam lobe.
If your are installing new lifters on the old cam then there could be some concern. The K-motion are excellent. I have them and recommended to many without any issues. 

[gnonyx]

How to do you know when it's time to replace the valve springs?