Engine: Valve Spring Tech - Rev Happy

[JoeThaMan]

Valve Spring Tech - Rev Happy
We were nothing less than thrilled about the performance of the 406ci small-block we built for January's "Old School Meets New" showdown. Faced with a formidable 402ci Gen IV opponent, our mondo-cammed motor matched its high-tech opponent pony for pony, churning out 582.9 hp and 532.7 lb-ft of torque. But even as we celebrated our creation's prodigious power output, we began to wonder if we'd left something on the table. Our peak horsepower number happened at 6,300 rpm, at which point the power curve took an abrupt nosedive. "It's going into valve float," said our dyno guru, Westech's Steve Brul. With that, we decided to see if we could get better control of our 406's valves and moderate the post-peak power drop.
Our first step was to call in some professional help, namely Comp Cams engineer BillyGodbold. We shared our dyno-day observations, and as it turns out, valve float, whichindicates loss of lifter contact with the camshaft lobe, isn't really an accuratedescription of what was happening in our 406's valvetrain. The issues are much morecomplex than that. We don't have room here for a dissertation on valvetrain dynamics,and fortunately, Godbold was able to give us the info we needed in layman's terms.Better yet, he was able to prescribe a solution, and an effective one at that.
Godbold described the phenomenon we experienced as "a very light valve bounce."Unlike valve float, valve bounce indicates that the valve is not staying seated. "Thespring mass itself wasn't enough to hold the valve down," Godbold continued. "Thespring starts to surge, so the valve control isn't good. When a spring is having problemscontrolling its own mass, it doesn't have as much ability to close the valve, and doesn'thold it closed. It can even push the valve open."
Substitute the word "resonance" for "surge," and you've got a quick explanation of ourproblem. All valvesprings resonate at a certain frequency, and they reach this frequencyat a given rpm. Godbold calls this the spring's limit speed, but it isn't necessarily tied tohigh-rpm antics. "When a spring gets close to the limit speed, it resonates," he told us."Many people think it happens at high rpm, but it actually happens whenever the springapproaches its limit speed." This resonance, according to Godbold, is a function of both aspring's rate and its mass. "As spring rate goes higher, frequency goes up," he told us."And as mass goes down, frequency goes up."
Although spring limit speed isn't always tied to high rpm, in this case, our spring's limitspeed was close to the engine speed at which our 406 produced peak power-thus thespoon-shaped dip at the end of our dyno runs. What we needed to combat the resonanceissue was a lighter spring that also has a higher natural frequency. Godbold figured that abit of Gen III/IV tech was in order, specifically a set of beehive-style valvesprings, firstintroduced for the Gen III LS6 powerplant.
"The nature of a beehive spring is that it has a progressive rate," Godbold explained."Each coil has its own resonance frequency. It's not just magic-there's a reason itworks. It's hard to make the whole thing resonate." Remember, however, that resonanceis also a function of a spring's weight, as well as its spring rate. Higher spring rateusually leads to a physically heavier spring, but using a beehive spring allowed us tomaintain the same spring rate while cutting valvespring and retainer weight in half."All we did was move the limit speed up, and the limit speed was close to peak power,"Godbold summed up. When compared to the "gorilla method," which would havemandated a bigger, heavier spring, this is a finesse approach. We are actually able toobtain better control with less seat load, open load, and spring rate by substantiallyreducing the mass, thereby increasing the natural frequency. Our post-peak dip is gone,and the thing revs to seven grand without a complaint. Sure, power still drops off after thepeak, but not as abruptly-up high, our rev-happy 406 is now making 40-somehorsepower more than it did. We'll take it.

Quick NotesThe Mission
Control high-rpm valve instability on a 406ci stroker small-block
The Bottom Line
A set of beehive valvesprings eliminated our post-peak power drain.
Cost
$500
HEAVY LIFTING
Before submitting our Coast High Performance-built 406 stroker to a round of high-rpmdyno testing, we installed a set of Comp Cams Pro Magnum hydraulic-roller lifters. Theydon't look any different from the regular High Energy lifters, but they're internallydesigned to perform at higher engine speeds. "The Pro Magnum lifter has less oilvolume," Comp's Billy Godbold explained. "The valving and geometry are set up tohandle high rpm." These lifters also have a low bleed-down rate and less plunger travel,which means they require a bit more attention when it comes to setting preload. Theyaren't, however, a cure-all. "They'll solve a lifter issue, not a valve issue," said Godbold."The lifter was fine; the valve was bouncing." Indeed, Comp's regular-issue handled our6,500-rpm abuse just fine. Looking to the long run, however, we went for the upgrade.Godbold endorsed our choice: "It's set up to be a very stout lifter. It's really goodinsurance."
WEIGHT-LOSS
To a certain extent, installing a stiffer valvespring improves valve control and reducesissues like valve bounce. On the other hand, stiffer valvesprings tend to be heavier, andweight is the enemy when it comes to high-performance valvetrains. Heavier springs areharder to control, and are harder on the rest of the valvetrain. Installing beehivevalvesprings allowed us to have our cake and eat it too. Our springs had nearly identicalseat and open-load figures, but the newfangled beehives weigh nearly half as much, andstayed in control where the traditional coils strayed.
Old Beehive Difference Spring 114.2g 69.5g -44.7g Retainer 15.7g 6.0g -9.7g Total -54.4g

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