Here’s the valve spring technology breakdown that only top industry experts have known about, until now!
With 50 years of race-winning engine building experience, David Vizard hosts episode 4 of Power Tec 10 with the goal to educate race engine builders and the home mechanic engine builder alike on new valve spring tech. Taken at face value, a valve spring looks like a pretty simple part. Many people think that if the spring gives the correct preload on the valve seat, the over the nose spring forces are in line and its made of good, quality heat treated wire then that’s all they need, but with his experience in valve train testing David says there is more to it than that.
The History of Valve Spring Breakage
Prompted by the fact that spring breakage was a very common problem, David was involved with a lot of valve train testing for Pro Stock applications in the late ‘90s. During which time, in 10 runs using the best valve springs available then, a Pro Stocker would have around 15 springs replaced. That equates to the destruction of more than one valve spring per run, allowing for issues like valve float to determine the winners and losers of the race.
With the Pro Stock issue being a major deal, spring manufacturers felt a push to look into better material and different spring and wire designs. By 2005 the issue of valve springs breaking as often as they did was largely overcome by turning attention to additional considerations like spring mass, spring rate, and resonant frequency.
With the ever advancing automotive industry moving almost as fast as the aerospace industry, valve springs that were top quality back in 1995 or 2000 do not compete near as well up against todays valve springs and most of the advancements that have been made were due to taking these additional considerations and building on them.
Improved Valve Springs Come Into Play…
Starting with the COMP Cams 924 valve spring, with its respective retainer, David dissects the mass, spring rate, and resonant frequency of it and two more modern style valve springs. The 924 weighs a little over 142 grams with an install height of 1.8” plus another 10th of an inch on top for the retainer. Setting the spring tester to 1.9 inches, the amount of preload this spring produces is 140 lbs.
At .625” of lift, the over the nose pressure is right at 350 lbs. and that is very close to coil bind. As the valve closes and the 924 starts to decompress, all the coils except the bottom two and top two are working coils. In other words almost the whole spring is still in action constantly. The 924 valve spring has a resonant frequency ranging from 350-550 hertz (cycles per second) over its opening envelope for an average of 450 hertz.
The beehive spring and retainer weighs 85 grams and is a little shorter than most conventional valve springs. That is 40% less mass than the 924 and would be the equivalent to swapping all of an engines steel valves for titanium valves. Installed on the spring tester that is still set to 1.9”, the preload is at almost 150 lbs., and at .625” lift it delivers 360 lbs.
So this shorter spring with less compression on it is actually delivering more poundage. Like the 924, its resonant frequency starts out at 350 hertz, but as it’s compressed to .625” lift, it ends with well over 1000 hertz. Further more, when the beehive is fully compressed only the top two coils are working coils offering the highest preload on the valve train at full lift. Then as it’s released, one by one the coils are brought back into operation.
Taking things a step further, the conical style valve spring essentially takes the best attributes of the beehive, the smaller coils of the spring, and spreads it out over its entire length. It weighs only 90% percent of the beehive spring at just 76 grams and utilizes only slightly thicker wire. Like the beehive, set to 1.9” it delivers 150 lbs. of preload. However, when compressed to .625” of lift it puts out just shy of 480 lbs. The conical style spring’s resonant frequency is higher as well. Because of all of these attributes and the fact that it is a stiffer spring meant for higher RPMs, it will outpace the dual 924 spring very easily and by a measure of a 2000 RPM margin.
Adding It All Up
Now what does this all mean? Keeping in mind that the core function of a valve spring is to control the valve train, the spring has to control not only the mass of the valve train but its own mass as well. This is where the weight of the valve spring comes into play. The lighter the spring, the less valve train mass there is to control and the higher RPM the spring is able to handle. While it is possible to lighten the mass of the 924 valve spring with the use of titanium retainers, titanium retainers are expensive when compared to the beehives retainer which is still lighter than the titanium one. Taking valve train weight reduction to the next level, the conical design is in a league of its own.
The spring rate effects the amount of pressure kept on the valve train throughout the springs travel from preload to over the nose and back. Looking at the 924, the preload and over the nose poundage is good for a street/strip application with a fairly aggressive cam profile. However, due to the beehives shape it produces a variable spring rate. As the spring is compressed the lower coils close on one another in order until only the last two coils are working coils.
This accomplishes two things:
- It takes the fully compressed coils out of the equation so that they no longer represent the mass that the rocker has to move
- It significantly increases the over the nose poundage while keeping the preload in the same ball park as the 924
Once again, because it takes the best parts of the beehive, this process is magnified by the conical design.
If you could see inside the valve cover of any engine while it was running, no matter what springs are under it, you would see the coils of the valve springs bouncing around as the valves close. This is the beginning of spring surge and it causes a decrease in power and is due in part to one of the biggest factors in spring design. Playing a major role in a springs ability to not get in its own way is its resonant frequency.
Ideally, the resonant frequency of the spring needs to be 10 times higher than the frequency with which its valve is opened. For example an engine opening the valves 50 times per second would do best with a spring that has the resonant frequency of 500 hertz or 500 cycles per second. With nearly double the resonant frequency of the 924 when compressed to over the nose, the beehive can look after itself when in motion far better, insuring better control over the valve train as the valves are closing.
Can you guess how the conical design compares to the other two designs? To top blowing the other two designs out of the water, the conical design is also available as a double. With two springs that have very different resonant frequencies, it will fight surge extremely well.
Street/Track Valve Springs, And Beyond!
Comparing the three designs with all the information laid out on a graph, it is easy to see the advantages that the beehive and conical springs have over a conventional double valve spring.
The beehive is doing the job with 7% more available spring force and 40% less weight, and the conical tops that with even more delivery from even less mass. When looking at spring rate of the beehive versus the 924 there’s not much difference until you reach the end of its travel where the beehive spikes. What this tells us is that the beehive is an effective replacement for the 924 in terms of spring rate, but offers better control at maximum lift and higher RPMs. The conical valve spring is a very stiff spring that is ideal for a very aggressive cam profile that also needs to turn at a high RPM.
However, looking at the resonant frequency really separates the men from the boys. The 924 has the typical resonant frequency of any dual valve spring as they don’t vary too much from this standard. The beehive is significantly better and the more lift you put into the valve train the better it gets, very much like the conical design which is in a league of its own. This is why it is important to use a beehive or conical valve spring within 25 thousandths of its coil bind height when the valve train goes over the nose.
Even though the conical valve spring is clearly the best of the best, and the beehive is miles above the 924 style, each valve spring has its unique advantages in certain applications and it is important to talk to your tech at COMP to see which would be best for your specific cam profile. Please do not hesitate to contact your friends at COMP Cams for more information on valve springs or for any of your other valve train needs.
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