Why shim to within .050" of coil bind?
11-23-2006, 09:45 PM
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Why shim to within .050" of coil bind? Most springs give an install height, often 1.800" for example. If you install the springs to within .050" of coil bind then your install height may be reduced to say 1.750", thus significantly increasing the seat pressure. Is the rational harmonics or what???
11-24-2006, 06:39 AM
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OK but if you look at it logically the bigger the lobe the less seat pressure. Case in point, I'm doing a 408 iron block and using a Comp XER 244/248 .612/.615 using PRC springs. Install height of 1.80- coil bind 1.07= .730- .615 lift=.115. To take the springs to .050 would require an install height of 1.735. OK now let's say we go with a bigger cam with an LSK lobe, .650 for instance, which with the higher lift theoretically would need more seat pressure but it's not getting it .730- .650= .080- .050= .030. Subtract that from the 1.80 install, and you have a new install height of 1.770. So bigger cam= less pressure, the opposite result of what you're looking for. Is that correct?
Last edited by bigdsz; 11-24-2006 at 12:53 PM.
11-24-2006, 07:25 AM
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I am not implying that shimming the springs tighter than the mfr spec is bad, what I am questioning is the arbitrary shimming to within .050 of coil bind. Higher lifts to me generally translate into more potential valve float, however the higher the lift the less actual install pressure using .050 as the standard. There must be other reasons for this practice.
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11-24-2006, 11:44 AM
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In the instance above, it would probablly require stepping up to a better spring. You don't neeccesarily have to shim your springs to within .050". If the spring is stout enough to hold the lobe, there is no need to shim, however, if you want to throw in more cam and not change springs, shimming may be necceasery.
11-24-2006, 12:30 PM
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Originally Posted by bigdsz
OK but if you look at it logically the bigger the lobe the less seat pressure. Case in point, I'm doing a 408 iron block and using a Comp XER 244/248 .612/.615 using PRC springs. Install height of 1.80- coil bind 1.07= .730- .615 lift=.115. To take the springs to .050 would require an install height of 1.735. OK now let's say we go with a bigger cam with an LSK lobe, .650 for instance, which with the higher lift theoretically would need more seat pressure but it's not getting it .730- .650= .080- .050= .030. Subtract that from the 1.80 install, and you have a new install height of 1.70. So bigger cam= less pressure, the opposite result of what you're looking for. Is that correct?
By your example, following the "shim to .050 coil bind" rule, your .615 lift cam requires an installed height of 1.735. Your .650 lift cam requires an installed height of 1.700. Correct me if I'm wrong here, but wouldn't the seat pressure be higher with the installed height of 1.700 (.650 cam) as opposed to the height of 1.735 with the .615 cam? I mean, if the seat height is shorter (1.700 vs. 1.735) then it's gonna have more pressure, right?
I mean, if mfgr's spec is X lbs of pressure at 1.800 installed height, then pressure at 1.735 is gonna be X plus Y, and pressure at 1.700 is gonna be X plus Z, with Z being a greater amount than Y. The more you compress the spring, the more seat pressure, right?
If I'm wrong here, then I just ain't seein' it right...
There are some very knowledgeable people on this board when it comes to valvetrain specs, I'm sure they'll let us both know if I'm off base here.
11-24-2006, 12:35 PM
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On a side note, to address your original question as to why we should shim a spring to within .050" of coil bind...
I ran across it somewhere in my research here and took notes, and I think it came from Patrick G (who'm I've come to consider one of the valvetrain guru's here), that the reason behind shimming to with .050 is to eliminate spring surge, which helps with longevity of valve spring life. To be honest I ain't exactly sure what that all means, other than to conclude that "spring surge" is a negative to be controlled in an effort to maximize spring life (a good thing).
I ran across it somewhere in my research here and took notes, and I think it came from Patrick G (who'm I've come to consider one of the valvetrain guru's here), that the reason behind shimming to with .050 is to eliminate spring surge, which helps with longevity of valve spring life. To be honest I ain't exactly sure what that all means, other than to conclude that "spring surge" is a negative to be controlled in an effort to maximize spring life (a good thing).
11-24-2006, 12:42 PM
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bigdsz, I just checked your math, and I see the error, and you're right with your analogy. Basically, you have a typo in post #4, and when you typed 1.70 you should have typed 1.770 which would make your math correct and the analogy correct, too...
Please disregard my post #10. Perhaps post #11 still applies?
Please disregard my post #10. Perhaps post #11 still applies?
11-24-2006, 12:57 PM
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Cool, I learned something new today...
Does the varying diameter of a beehive spring work to control these harmonics, as opposed to the inner dampening spring of a double (or Triple) valvespring?
Does the varying diameter of a beehive spring work to control these harmonics, as opposed to the inner dampening spring of a double (or Triple) valvespring?
11-24-2006, 01:00 PM
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yeap, this is why the 918 is such a good spring and most poeple refuse to use them out of pure phobia. Bottom line, they are better than most duals for harmonics on any cam to .620 lifts (assuming installed at correct height/pressures for cam used)
11-24-2006, 01:32 PM
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Predator thanks for your illustration. FWIW I have run Comp 978's for years, they have 2 springs with a third flat wound damper spring. Very cheap, I think like $70 and no problems, other than you can't go above about .600 lift. That's why I'm going with the PRC's.
11-24-2006, 04:10 PM
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Originally Posted by PREDATOR-Z
yeap, this is why the 918 is such a good spring and most poeple refuse to use them out of pure phobia. Bottom line, they are better than most duals for harmonics on any cam to .620 lifts (assuming installed at correct height/pressures for cam used)
I'm still working on it. Almost done though. 
11-24-2006, 04:24 PM
#20
Originally Posted by Judge Smales
So can they be used with the 228/232 cam everybody has been talking about?
