Valve Spring Tests

[salvageV6]

Tested 2 each of: Stock 112K mile GM valve springs with cups and 2 Comp. Cams. 980's no cups.

Measured distance traveled to get three spring forces in lbs. Kinda backwards of usual tests but worked for me.

Used a calibrated and very accurate Instron machine at work.

Here's my results.

Stock Springs

Force Spring 1 Spring 2
80lb. .334" .338"
85lb. .353" .355"
90lb. .371" .372"


Comp. Cams. 980's

Force Spring 1 Spring 2
80lb. .283 .276
85lb. .300 .294
90lb. .316 .311

Springs were tested with a solid steel machined retainer with spec.s equal to the stock retainers such as shoulder on it excepting is was perfectly solid on top and perfectly flat.

I was amazed at the differences between the 2 types but was impressed with the closeness of the two samples. Woulda tested more but I only brought in a small sample in case they couldn't do it.

I'm glad I didn't use the cups with the 980's.

[Steve Wood]

I assume the distances quoted are compressed distances? Did you measure the uncompressed spring so you could calculate the pressures at suggested installed heights and compare to specs?

[salvageV6]

Yes they each were touched off and zero'd so each spring is compressed distance.

All the uncompressed springs were just about the same height?

Didn't have the specs. with me so.....

Doesn't matter what the installed height is really for my test. Just showed that for the range of pressure theoretically near the installed height there is a lot more force with the Comp. Cams vs. worn out stockers.

But then again everyone already knew that.

Hey don't get technical on me here....

I only had a half hour to measure them all too.

Well, I numbered them all so I guess I could get some exact measurements for each one. But since they are on the cars I think I'm glad I didn't use the cups. Wish I had a new stocker to compare to and an old 110K mile Comp Cam 980 to use too.

[This message has been edited by salvageV6 (edited November 14, 2001).]

[Steve Wood]

Stock height is 1.72

I am not sure what the Comp springs are quoted as (at what height)

I think the factory springs were claimed to be 74-82# at 1.72 if I looked at the right column.....I was curious to what the Comps came out to be at that height...I would guess in the 80s.

[salvageV6]

I brought in a new baggie full of springs today. Guess what I forgot my machined retainer and I wasn't about to ask to get another one made.

So the test can wait til tomorrow and I will shoot for the installed heights. Yup 74-82 is in the right column. Not sure if I'm gonna compress them all the way to spec. and about 185lb. but maybe.

[Steve Wood]

Well, that is at full lift...really no need, I think.

[salvageV6]

Not knowing much about what destroys cams....

Wouldn't it be the high side pressure on the ramp of the cam? Isn't that actually more important than the low spring pressure or closed position? Just wondering?

Then again if the low side is too high a pressure you can guarantee the ramp ain't gonna be good.

[Steve Wood]

well, the open pressure probably does more damage but it is pretty linear for a given spring so the low end is what determines the total...at least for springs of a similar ilk.

Maybe...*g*

[salvageV6]

Here's some new and exciting results!

Three new Comp. Cams. 980's and 3 worn out GM stock springs with cups.

All measured to installed height of 1.727" Units are in lbs.

Stock Springs (used)
1 61.93
2 67.01
3 64.38

Comp. Cams. 980's (New) NO CUPS
1 86.04
2 84.92
3 84.60

Yup, I'm still glad I didn't use the cups with the 980's.

[Steve Wood]

I would have bet the stock ones were in the 50's! The 980's are good springs...just about ideal, I think...

Interesting results which support changing higher mileage springs, I think.

[salvageV6]

Guess I should have said the stock worn out springs had 112K miles on them from the GN.

I agree the 980's are about perfect if the stock spec. is more ideal than what was installed as the stock spring?

60's is still way low compared to the spec.

I think the butt dyno at WOT can tell the new ones did some good.

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WE4, Daily Driver, PTE51, 43lb. Bosch, THDP race cat., Postons Headers, 21/2"SS Ultraflows and pipes, 16 pos. Maxeffort thumbwheel chip, Bilsteins, Airbags/snubber,snows, 307 adj.reg./ gauges,scamaster and D.S.,BSTC,small stuff too. V4 IS IN!!! Not legal for racing.

GN loaded, car #2. 112K miles. Accufab reg. 160stat.,Scanmaster, Bilsteins, Moog springs.