Advanced Engineering Tech - Let's talk vavle spring rates

View Full Version : Let's talk vavle spring rates

LIL SS
08-25-2012, 04:28 PM
When a spring is used and starts to loose strength, would it not loose strength across the board? (installed height and max lift showing less pressure than advertised or new)

For instance, if a spring is rated as:
145lbs @ 1.80 install
450lbs @ 1.15 install

Then spring rate should be 469lbs correct?
1.80 - 1.15 = .650
450lbs - 145lbs = 305lbs
305lbs / .650 = 469lbs per 1" of compression

I just pulled some springs off my motor that have very little use. Maybe 500 miles 10 dyno pulls and 20 passes at the track. Here is where they average. I used a Comp Cams Rimac for my testing (I did not test them when I bought them, but will next time I buy springs):

145.5lbs @ 1.80 install
411.4lbs @ 1.15 install

I get right about 409lbs of rate
1.80 - 1.15 = .650
411.4lbs - 145.5lbs = 265.8lbs
265.8lbs / .650 = 409lbs per 1" of compression

So the advertised numbers are right where they need to be for the installed height of 1.80" but they sure don't have a spring rate of 469lbs (or at lease don't anymore).

I am scratching my head wondering if they ever had the spring rate advertised. Seems to me if they did, 1.80" would be less than 145lbs as well.

Would 1.80" not be closer to 127lbs?

Here are the symptoms:

On the dyno it laid over very quickly after about 6,500. Didn't notice this previously but looking at the dyno sheet, it appears to have some surge going on between 5,300 and 6k rpm. (dyno attached)

At the track, it would lay over at 1,200-1,250 feet and you could here what sounded like valve float. This was not noticable at the dyno as it was accelerating the rollers fairly fast.

Looking at the data loger from passes at the track, once it hits 6,700 in 2nd gear (power glide) you can see the rpm bounce up and down a bit (pic attached. Lower red line is RPM scalled from 6,500-7k for resolution purpose. You can't see what I am talking about with out doing that)

S10xGN
08-25-2012, 08:24 PM
I wouldn't think it'll show up as linear. As long as the free length doesn't change, the further away from free length, the more deviation from spec.