Any advantage to higher [i]open valve [/i]spring pressure? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 04-11-2007, 03:04 PM   #1
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Default Any advantage to higher [i]open valve [/i]spring pressure?

This thread is an "offshoot" from:
http://www.bonnevilleclub.com/forum/...ic.php?t=75760

I'm looking to upgrade valve springs along with a higher-ratio rocker install on a 1998 L36.

With aftermarket springs, I understand the advantage of higher closed valve spring pressure as regards preventing valve float...but is there any advantage to significantly higher open valve spring pressure?

(Bear in mind we are talking shift points in the 6000 to 6250 rpm range, on a stock L36 cam)

Without detailing all the calculations, let me give you some examples I worked up that give equal closed valve pressure, but different open valve pressures:

Stock L36 springs/stock retainers/stock rockers:
70 lbs at 1.720" (closed), 227 lbs at 1.277" (open)
(based on estimated 355 lb/in spring rate)

LS6 springs/CompCams (or LS6) retainers/1.8 rockers:
90 lbs at 1.800" (closed; 29% higher than stock), 279 lbs at 1.302" (open; 23% higher than stock)
(based on estimated 380 lb/in spring rate)

CompCams 105# springs/Manley "thin" retainers/1.8 rockers:
91 lbs at 1.845" (closed; 30% higher than stock), 247 lbs at 1.347" (open; 9% higher than stock)
(based on published 313 lb/in spring rate)

In these examples, both modded setups give an increase in closed valve pressure around 30% (this is good); however, owing to a higher spring rate, the LS6 example gives a significantly higher increase in pressure at open valve (23% over stock) than the CompCams 105# / Manley retainers example (only 9% over stock).

I assume this higher open valve pressure is what could lead to increased wear on the timing components...but is there any performance reason why I should WANT the higher open valve pressure of the LS6 springs vs. the CompCams 105'*? Wouldn't this shut the valves faster?

(The LS6 example does have the advantage of being around $100 cheaper, while the 105#/Manley example has the advantage of greater headroom for additional lift in case I got totally crazy and added and/or swapped in a cam later...but maybe I'm really just looking for reasons not to spend the extra $100 )
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Old 04-11-2007, 03:37 PM   #2
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I don't think there is any advantage to the 90# springs because of the higher open valve spring pressure.
If you had a wild cam with an extreme ramp rate, you would need that extra pressure to keep up.
The 105s have shown to do a good job of eliminating float even with bigger n/a cams. Generally, the ramp rate of an aftermarket n/a cam is less than that of a */c one.
If anything, the 90s will cost you a small amount of power since your adding unnecessary force against the rocker.
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Old 04-11-2007, 03:43 PM   #3
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The only thing I can think of is that the higher pressures while open will help snap that valve closed sooner, ensuring there is no slop in the valves. Other than that, you don't have a cam that needs crazy pressures. In fact, there have been many people who have run a GT1 or IS1 cam without changing springs at all. I would doubt you really need stronger springs to rev a stock motor up to 6000rpm or even 6250rpm.
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