By now, the LS performance world is aware of the fact that the installation of a serious performance camshaft requires upgrading the factory valvesprings. The valvespring upgrade is usually necessary for two reasons, increased lift values and increased engine speeds. The factory LS1 valvesprings will tolerate .520 lift (LS6 and LS3 slightly more), but aftermarket performance cams can reach .624 lift in some applications. Attempting to run a high-lift cam with stock springs will result in coil bind and catastrophic failure of expensive valvetrain components. The cure is to install springs that were designed for the increased lift. Along with the increased lift is increased duration, which in turn increases the effective operating speed. Additional engine speed requires increased spring pressure to allow proper valve control. Insufficient spring pressure can result in uncontrolled valve movement, the two most common problems being valve loft and valve bounce. Valve loft occurs during the valve opening event, when the roller lifter loses contact by launching off the top of the cam lobe before settling back down on the closing side. By contrast, valve bounce occurs as the valve is closing. The lifter comes down hard on the heal of the cam only to bounce back up and down before settling the valve in the closed position.
Obviously, these valve-control-related issues, associated with insufficient valvespring pressure, are the reason why camshaft manufacturers offer valvespring upgrades. The obvious answer might seem to be to install plenty of spring pressure to keep the issue in check, but (as always), there is more to the equation than the simple “more is better” theme. Just as it is possible to have insufficient spring pressure, so too is it possible to have excessive spring pressure. Excessive, in this case, covers both the lift and engine speed portions of the equation. It stands to reason that if you run a .600-lift cam, the valve springs must not coil bind at .550 lift or even .600 lift, nor should they coil bind at .700 lift. According to the experts, valvesprings should run with .060 coil-bind clearance, but they actually offer the most control when run closer to coil bind (.030-.040). Excessive spring pressure, defined as more than required to provide adequate control, can also cause prematurly wear rates in the cam lobes, rocker, and valve tips. On LS applications, the combination of high lift and excessive spring pressure can also shorten the life of the valve guides (especially the after market bronze variety).
One final fact, and the reason behind this lengthy dyno session, is that increased spring pressure consumes power. Simply stated, it takes more power to compress the increased spring pressure. What this means is that while a valvespring upgrade is always part of a performance cam swap on an LS application, there is a loss in power associated with the spring swap. The gains offered by the cam are huge and the necessity of the valvespring upgrade can't be ignored, but we were still curious as to just how much power the springs absorbed. To illustrate this fact, we performed a series of tests using an LS3 crate motor supplied by Gandrud Chevrolet. Since the stock LS3 springs would not allow a high-lift performance cam, we decided to compare the stock springs to a set of Comp 26918 beehive springs on the stock cam. We then installed a custom cam from Brian Tooley Racing, along with one of his dual valve spring upgrades designed for high-lift (.600+) cams. This procedure allowed us to compare the stock to the beehive on the stock cam then the beehive to the double springs on the performance cam.
The LS3 test motor was run using a Holley HP stand alone management system, and complete fuel system from Aeromotive, that allowed us to dial in the air/fuel and timing. No changes were made to the timing curve, but the change in power offered by the valvesprings did lean out the air/fuel mixture slightly (which we adjusted back to an idealized 13.0:1). The test motor also sported a set of long-tube headers, feeding a 3-inch exhaust and mufflers. The stock springs were run with the stock cam and intake manifold, but we performed an intake swap before installing the performance cam. Equipped with the stock cam and stock springs, the LS produced peak numbers of 516 hp at 5,900 rpm and 501 lb-ft of torque at 4,800 rpm. Remember this was run on the engine dyno with no accessories (an electric water pump) with optimized air fuel and timing and a set of long-tube headers. The LS3 was perfectly repeatable, an important point given the fact that we were looking for only minor changes in power with a spring swap. Swapping over to the 26918 beehive springs from Comp Cams resulted in a slight drop in power to 512 hp and the same 501 lb-ft of torque. The power losses associated with the increased spring pressure were only present above 5,500 rpm.
Next up, we prepped the motor for the second spring test. The LS3 received a cam and intake swap. In went a Brian Tooley Racing (BTR) cam that offered a .624/.590 lift, a 232/248 duration and 114-degree LSA. Knowing any changes in power would be most prevalent at higher engine speeds, we decided to perform an intake swap designed to enhance power production higher in the rev-range. The stock LS3 intake was replaced with a fabricated unit from Procomp Electronics. Though worth power gains higher in the rev range right out of the box, the Procomp intake was modified with the addition of radiused entries on each intake port. Equipped with the new BTR cam and fabricated intake, the LS3 now produced 590 hp at 6,800 rpm, and 493 lb-ft of torque at 5,800 rpm.Swapping out the beehive springs for the dual-spring upgrade from BTR resulted in almost no change in power. The peak numbers now registered 589 hp and 492 lb-ft. From this test we can deduce that while a valve spring swap will reduce power, the minimal loss is more than offset by the safety and extra power offered by the performance cam.