Valve spring question

At what point (rule of thumb) should valve springs be replaced when checking during the race season? Example, if the spring was installed at 260# at what point should the spring be replaced as the installed pressure is reduced when checking? Or is it possibly when the engine starts to slow at higher rpm?

So I haD a baseline pressure that will cause me problems in my engine. It is 230lbs seat pressure on the intakes with the spring rate I was using at 7300.

I have changed to a different spring rate/spring so I am still working down to find out the minimum. This may not help but as long as you are keeping control of the valve they are good in my opinion but you just don't have as large of a margin for error.

I try to give myself room so if I lose 10% and still have control that gives me a change point number if that makes sense to you. This only applies if you know where you lose control.

100 runs

quote:

Originally posted by rusty:
100 runs

I'm too cheap for that.

If you check your springs regularly, I'd say when they loose about 10% or so of seat pressure. On my stuff, they only time I've changed them is when I broke a spring.....and I'm running about 350-375 on the seat and 1150-1200 open, seeing 7800-8200 every pass..they hold up well.

I ONLY run PSI springs though, no longer PAC...long story

I run PSI springs and when they are new they set up at 320 lbs on the seat. 150 or so passes later I check them they are around 300-310 range. When I check them and they are 290 range and I replace them. Basically when they lose around 10 percent.

That's usually a 3 year cycle for me. Mine were replaced in 2024 and now they will get replaced for 2027.

quote:

Originally posted by moparacer:
I run PSI springs and when they are new they set up at 320 lbs on the seat. 150 or so passes later I check them they are around 300-310 range. When I check them and they are 290 range and I replace them. Basically when they lose around 10 percent.That's usually a 3 year cycle for me. Mine were replaced in 2024 and now they will get replaced for 2027.

Does the exhaust valve spring test as low as the intake valve spring? If no, do you still replace both?

quote:

Originally posted by markemark:

quote:

Originally posted by moparacer:
I run PSI springs and when they are new they set up at 320 lbs on the seat. 150 or so passes later I check them they are around 300-310 range. When I check them and they are 290 range and I replace them. Basically when they lose around 10 percent.That's usually a 3 year cycle for me. Mine were replaced in 2024 and now they will get replaced for 2027.

Does the exhaust valve spring test as low as the intake valve spring? If no, do you still replace both?

I think its weird, but they do seem to lose about the same amount. I pondered doing that one time trying to cheap out and do the exhaust to intake spring rotation but I could not see enough difference in the exhaust springs to justify it.

One thing you can do is use the old intake springs on the exhaust and only replace the intakes. Exhaust doesn't need the same pressure as the intakes as it's opening against pressure, not holding back vacuum or boost if that's the case.

I run different springs on the exhaust than I do on the intakes.

Ok, the 10% valve spring pressure loss sounds like a good point when changing.

I’m looking at the engine with 1098 runs that I just took out and keeping as the spare in the event the new rebuilt one going in has problems. The exhaust valve springs are 2 – 4 % down and intake 10 – 14% down. I’m going to replace only the intake valve springs in the event I need this engine to run again. This engine also needs new lifters as the needle bearing type installed are failing.

Surprisingly this engine makes the same power now as it did new installed 8 yrs ago. Thanks for the responses.