Very good catch!! My bad.... it should have been 60N per mm, the way I wrote it it looked like a torque which it is not.

Thanks for keeping me honest!!

 

 

I would think because they are built of a better alloy, tuned to a higher resonant frequency, and with surface treatments such as nitriding and nano-peening, plus the benefits of additional seat pressure and higher lift capabilities, can make them last an incredibly long time without pressure loss or fatigue-sagging over time common with most valve springs.

Then the obvious side-benefit, that if the OP ever does wish to install an aftermarket cam, he's already covered, and won't have to swap the springs yet again to handle the additional lift.

Broken LS6 springs are not uncommon, even on bone stock engines that have never been abused. They may have been improved in 2004, but still, their ill-reputation for longevity, especially on cars that get tracked and/or see extended use at high RPMs, would be reason enough for me to consider a more durable alternative.
Spring failures are nothing to mess around with. If you had one fail, and it didn't drop a valve and wipe out your engine, you are lucky!

Set up correctly and used within stock engine operating parameters, the PAC 1518 is a spring the OP simply will not break. And by no means overkill even for stock cam and valvetrain.
He can pull one out in 10 years, and probably find it hasn't lost a pound of seat pressure. I sincerely doubt you can say the same about even the "new and improved" LS6 spring.

 

That's ME! I feel I've gotten away REAL cheap on this one... had those keepers let go and let the valve drop I'd have been building a whole new engine over the winter.

This is what I'm banking on... the spring seems to be total overkill for use with the stock cam, but the compressed load at full lift with the 1518 is hardly higher than with the stock springs, so the 1518's should have a long, easy life.

And I'll be stress free driving the car knowing I've got the best solution to an all too common problem. With over 100k miles on this car I figured I'd never break a spring. Just goes to show it can happen at any time!

 

Y2Kvert4me,

Thanks for taking the time to put your post together and for your view on valve springs. I’ll try to share a little on this subject and if there is an interest we can deep dive even more. I will try and point out the things in your post I agree with and some things that I don’t, not necessarily my opinion, but information based on measured data.

I agree with you 100% that if the original poster has plans of going to a new cam with more than 14mm (.551”) lift in the VERY near future that going with the PAC 1518 spring might be a good choice.

Valve float occurs when the spring can no longer keep up with the rate of change of the valve going up and down. One of the main controlling factors is the spring’s natural frequency. This frequency varies based on spring compression on a conical designed spring. The data sheet for the PAC-1580 shows it to be 488Hz. The newer replacement LS6 spring is 580Hz. So, the risk of valve float with the PAC spring at a given engine rpm is greater compared to the stock spring for two reasons. One, the natural spring frequency and with the stock cam the PAC spring isn’t compressed far enough to reach the higher frequency point. It is a nice idea to plan for the future, but in the case of a valvetrain system, each component needs to be maximized for the even application for not only performance but also durability.

I won’t go into materials at this time other than to say the stock springs are made of some of the best material available and all springs are shot blast peened twice.

I believe what you referred to “pressure loss or fatigue-sagging” is controlled by what is known as a Heat Set process. The stock springs are tested and designed not to exceed more than 3% at maximum opening force for the life of the spring. Bottom-line, this really isn’t a factor of concern.

Let’s talk about valve spring durability. There are many factors that play into how long a spring will last. I would like to touch on just a one. The amount of stress on the spring plays a major roll on how many cycles it can endure before some part of the coil fails. If I spread the stress over a larger area the spring will last longer for a given number of cycles compared to the stress over a smaller area. So, the more coils I have the more area I have to distribute this stress. In the case of the stock spring I have a total of 7.2 coils compared to maybe 6 on the PAC-1580. Base on this I would expect at least a 20% advantage in durability with the stock spring compared to the PAC-1580.

I agree with your statement “Spring failures are nothing to mess around with” and I would want to do everything I can to reduce the risk of breakage. This includes sizing and selecting the spring that fits the current configuration as opposed to trying to select one for future use.

I disagree that PAC-1518 would be his best choice if he plans to stay stock for any period of time. I believe doing so increases risk for valve float and spring failure over the stock replacement.

 

Interesting data.

By chance would you have those design specs of the OE (2001-2003) LS6 springs, the ones people are commonly breaking? And if so, what do you view as the cause of those failures?

I am by no means a spring engineer, I do see what is and isn't breaking for people.

 

I can not tell you for sure what the primary issue was. What I can tell you is the earlier spring had the same number of coils as the PAC 1518, 6 versus the newer spring with 7.2.

 

Interesting. Looks like the bottom line is matching the spring pressures to the cam thats being used. The brand one chooses seems irrelevant if the specs are whats being considered first & foremost.

 

I believe both are important, the brand and the specs. A good brand (source) should give you the means to select the best spring for the system.

 

I'm not going to get into arguing spring specs and the relevance in any individual application, but I will throw in a few things.

The LS6 spring and PAC1518 have the same number of coils. I have them both right in front of me and can assure you of this.

Harmonics will not be an issue. It is an advanced idea and definitely is something to consider in many applications, but it will not be an issue in this application at all and definitely won't cause any valve float.

Which is better for a stock application can be argued all day, and I won't get into that. All I can do is refer to experiences with the large number of applications for which we have sold both springs. We have had no problems, and that includes many people with stock LS6 engines looking to change springs after breaking a stock spring who have gone with the PAC springs.

Whatever spring the OP feels the most comfortable will suffice I am certain. If he were to call me looking for an alternative, I would never hesitate to throw the PAC springs into the running. Many people simply don't feel ok with the stock springs once they have broken one, and this is the direction we steer them in that situation. I am not saying the LS6 spring is no good, but I also feel comfortable saying there are no viable negatives to the PAC spring where I would rather run an LS6

 

No arguing for me, just give the supporting info or data.
So which spring doesn't meet the spec's as shown on the data sheets? How many coils do you count on each of the two springs you have right in front of you?

I don't recall saying anything about harmonics, I was talking the natural frequency of the springs and this does matter and is one of the key items in the design of a spring for a given application. It is one of the primary reason for conical designed springs.

Again, no arguing, just give the supporting info or data and the end user can make their own choice.

Would you blame them for feeling this way with all the miss information out there? The sad thing is some after market suppliers play on the fact that some early springs were bad and now ALL springs from that source must STILL be BAD and then steer folks to something else based on unwarranted fear.

There are NO fits all springs. If you want the best overall valvetrain performance and durability, each component has to be selected for that give application. Anything less is a compromised system.

 

Check out this video:

http://www.youtube.com/watch?v=_REQ1...eature=related

According to these guys, insufficient spring force is shown causing valve bounce/rotation when seating. If this is true, increasing the seat force while minimising the increase in open force would improve the situation (which is what the PAC 1518 would do), no?

As far as harmonics/natural frequency (the same thing in valve spring discussions AFAIK), as long as the harmonic frequency was kept above a critical level it wouldn't be an issue... correct me if I'm wrong, but the natural frequency of the spring is measured at the installed height?

I'm no valve spring "expert", but I can digest technical stuff pretty well. I hope I can learn something here - keep it comming!

EDIT: I can't bring myself to say spring "pressure"... it's a linear force measured in lbs., "pressure" has nothing to do with it.

 

Hey guys not to take it off topic, but what might be the lifespan of the springs be? The ones i have are comp cams dbl spring not sure of the part/model #using this cam '214/230 .601/.575' 117 LSA with about
20,000mi non race, just spirited street driven . TIA

 

The video link you referenced can be miss leading because of what was use to capture the images. The video was done with what is called a strobe-tach. The strobe allows the capture of one image out of many. With a little bit of phase mismatch the valve will appear to be in slow motion, even though it is moving at a much faster rate. It can be useful but can also give you a false image. This false image affect is called aliasing. Here is an example;http://www.youtube.com/watch?v=ltMPMz37VPk&NR=1 Note how the prop blades seem to be disconnected from anything.

I'll cover your other question tomorrow..

 

Interesting discussion. Production part failures have been an effective marketing tool for the aftermarket suppliers for years, not all but most. It's relatively easy to issue psuedo-technical information about why your part is so much better that the OEM part and sell it to a mostly non-technical customer base.
I installed a set of used LS6 springs I bought for $25.00 from an individual who fell for the hype when I replaced my cam. My car gets autocrossed regularly and I'm quite happy with them.

 

The frequency of a spring depends on a number of factors, including the shape. The conical designed spring has some very unique features compared to a constant coil size spring. The frequency of this design changes as the spring is compressed. If you were to watch this spring in action with the aid of a high speed camera, the lower coils start to stack on top of each other. This stacking affectively changes the spring coil length and this is what causes the shift in its natural frequency through the valve cycle. The conical design also allows for a smaller lower mass spring retainer. A constant coil spring doesn’t change frequency as much compared to the conical. Again, if viewed with high speed imaging, at or near valve float all the coils start osculating at about the same time and the spring can no longer maintain the reactive force needed to track the cam lobe.

 

By conical, are you referring to the "beehive" shape? If so, I believe this is a moot point since both the OEM and PAC replacement springs are the same beehive design.

I think what you are referring to is a "progressive" wind spring where all of the coils are not equally spaced. This is common on suspension springs, the tighter coils at one end offering a softer ride for the first small portion of spring travel; these tight coils stack (bind) on each other leaving only the coils that are spaced farther apart and effectively increasing the spring rate (K) the farther the spring is compressed.

If this is what you are referring to, there's no need for the high speed camera to see this, just compress the spring and watch the coils.

This makes sense depending on what you are referring to as "constant", i.e. the coil spacing or the diameter of the spring? A beehive shaped spring only has the upper two coils reduced in diameter to fit the smaller lighter retainer, I would imagine any frequency change in that region of the spring is just a side effect of the diameter reduction requirement, no?

Any spring's natural frequency will increase as it is compressed. I would imagine that a progressively wound spring would give the Engineers the opportunity to "tune" the progressive end of the spring to not only offer the valve seating force required, but also introduce a second area with a natural frequency that would help cancel natural frequency oscillations in the stiffer upper portion of the spring as well.

A progressively wound spring would not offer the dual frequency cancellation effects at full lift since the progressive coils are "bound" at that point. The stiffer end of the spring would have to get by with its own single natural frequency.