What would be a good installed valve spring pressure for a stock motor with a double roller timing chain ? I am going to be replacing my valve springs early this spring with either Cottons 980's or Kirbans LT1 springs. Also I don't know if it is possiable to achieve the same exact installed pressure for each spring, so what is the general rule of thumb ? Thanks, Kyle.
Correct installed valve spring pressure
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chriss4655
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I.750 . It's pretty hard to get it exact with the heads on the car. But you should be able to get it close.
Thanks for the info, I have been doing some research on shiming the valve springs to achieve proper spring pressure, my plan is to purchace a valve spring height micrometer, a good valve spring pressure tester and a shim kit. After I measure the installed height of each valve I will be shiming each valve spring to achieve the desired pressure. The reason for me checking each valve installed height and valve spring pressure is I read that valve springs can very slightly or be off by several pounds between each new spring. Cottons 980 springs are advertised at 92lbs. @ 1.70 installed height, but the info I think I need is what pressure should the valve springs be set up at on a stock flat tappet cam and how many lbs + or - can each spring very ? So I can determine the installed height I need to set each valve at. I hope this makes since and that I am going about this right !!! This will be my first attempt at installing valve springs and I want to do it right the first time so please let me know what you guys think.
To get the correct poundage you need to know the exact installed height of each valve and the exact poundage of each spring.
Even doing it 'right' with all the exact tools, it's still not an exact science. The springs are going to 'take a set' quickly after being installed and the rules are going to change.
When I built my engine I wish I'd had the time to run a test. I was going to set them up with the poundage I wanted.... Then squish them in a vice over the weekend and check them again..... then let them sit a few hours and check the again.
Even doing it 'right' with all the exact tools, it's still not an exact science. The springs are going to 'take a set' quickly after being installed and the rules are going to change.
When I built my engine I wish I'd had the time to run a test. I was going to set them up with the poundage I wanted.... Then squish them in a vice over the weekend and check them again..... then let them sit a few hours and check the again.
Normally you would want at least 100 pounds on the seat for a stock cam. But if you have a spring tester and let's say you have 6 springs at your desired installed height at 105 and 6 at 100 always put the stronger springs on the intake valves because they are heavier than the exhaust.
Let me make sure I understand this correctly:
1) When testing valve springs with a spring tester and the desired pressure is 100lbs the installed height for each spring is going to be different, correct ?
2) Then I shim each spring to the desired height to achieve the desired pressure.
3) But because we only have a few different shims thicknesses (.015, .030 and .060) to use, we are either going to be a little over or under our desired pressure, correct ?
4) So after I install the 6 strongest springs for the intake, I am assuming I would match the remaining exhaust springs to the correndsponding intake spring pressures ? Meaning if #1 cylinder has the strongest spring on the intake the 7th strongest spring, out of the 12 should be installed on the #1 exhaust and so on, correct ?
Thanks for he help, Kyle.
chriss4655
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Stock cam and comp 980's without the factory spring cup , set the height 1.70 to 1.75 and you should be good to go!!! You trying to do this with the heads on the motor and motor in the car ?
I usually put the stronger springs on the exhaust side since they run hotter. To each their own I guess. In real life it probably doesn't matter.
Yes heads on the motor and motor in the car. I'll be installing the Comp 980's in early spring. I am just gathering all the tools and info needed to do the job right. This is my first time doing valve springs
Thanks again, Kyle.
Yes heads on the motor and motor in the car. I'll be installing the Comp 980's in early spring. I am just gathering all the tools and info needed to do the job right. This is my first time doing valve springs
Thanks again, Kyle.
What type valve spring compressor are you planning to use?
I plan on making one out of a old rocker shaft assembly similar to the one Cotton Performance sells.
