When setting up a valvetrain, power comes from a system that is well designed and in control. Such a system is typically more reliable, and for the vast majority of street/strip cars, having a valvetrain that simply works for 25k miles or so without constant adjustment is what you want. But you also want power. Control can be had with super aggressive combos, which might make power, but at the expense of longevity. It’s a trade-off; one that doesn’t have to occur. Why? Because you can setup the system to be reliable and perform. And here is how.
I generally recommend two rules when setting up a valvetrain as a “system”: light as possible over the valve side of the rocker and stout as possible on the lifter side of the rocker. See Figure 1. Figure 1. Valve Side Highlighted. Valve Side Recommendations
When I talk about lightweight over the valve side, I mean everything on the intake valve side of the fulcrum on the rocker arm. That includes the tip of the rocker arm, the valves, and the valve springs. When I say stout on the lifter side, I mean the lifters, pushrods, and pushrod cup. Both will be affected by cam lobes, which I will get to momentarily.
For valve side of the fulcrum, a lighter setup is easier to control, even with aggressive lobes. It requires less spring pressure for a given lobe and more easily revs. I typically recommend lightweight, hollow-stem valves for the intake valve, and solid stem valve for the exhaust. The weight is similar between the two, due to the size difference, but the added material helps the exhaust valve deal with the heat a bit better. I also recommend either lightweight dual valve springs with titanium retainers or beehive springs. Modern, nitride beehives have similar closed pressure to lower-end duals, but weigh much less, have better harmonics, and typically control a valvetrain to a higher RPM than a similar spec’d dual. However, some lobes or valvetrain combinations need the added spring pressures of a quality dual spring.
The rocker arm is a place where the moment of inertia or MOI can wreck the entire valvetrain setup, because an extremely heavy rocker is difficult to control, requiring additional spring pressure to achieve the same RPM potential as lighter options. One example is the stock steel LS1 rocker is very light over the nose of the valve, but aftermarket aluminum roller rockers are not. Even though they are aluminum, the added weight of the roller bearing, pin, and additional material to withstand the stresses of high valve spring pressure makes them less than ideal in certain applications. Further, the added weight requires more spring pressure than the stock, steel LS1 rocker, but, as we have seen in past failures, the aluminum is sometimes unable to take the added spring pressure without fatigue and failure. Currently, there are no perfect solutions for the LS1 – either scrub the valve guides due to side loading at higher lifts with the stock rocker or add more spring pressure to the system, adding friction, weight, and fatigue to an aluminum roller rocker.
I typically use stock rockers with upgraded trunions to handle cam lifts upto .630″ with 1.7:1 ratios per Brian Tooley's recommendation. Bronze guides scrub easier and may require roller rockers. In many cases, you can have the head manufacturer install powdered metal guides, which take the scrubbing action of the stock rocker arm without as many detrimental affects. Lifter Side Recommendations
On the lifter side, you want a lifter that can adequately hold the spring pressures applied to it. Any decent lifter is all you need, but I generally like short-travel lifters with link-bars. Link-bars provide added margins of safety versus the LS series plastic lifter trays. And the shorter travel lifter acts like a solid roller at higher RPMs, but does require precise preload across all valves. It’s time consuming and painstaking to measure all 16 valves for very small differences in preload, but the additional valve control afforded is fantastic. The control comes from taking the slack out of the system and allowing the cam lobe to transmit valve action without losing much transmission of force. To aid in this, I always recommend the stoutest pushrods that will fit. Even with regular, stock-type lifters, pushrod flex is a bad thing.
The bigger, stiffer pushrod deflects much less. When a pushrod deflects, it acts as a secondary spring, absorbing some of the lift action from the cam before it is transmitted to the valve and can actually try to vault the lifter off the cam, allowing it to loft before everything crashes back down once the pushrod recoils back into place. This is one reason why folks have to keep adding more spring pressures with aggressive lobes to counteract the lifter loft from the pushrod deflection. The problem is your lifter has to be able to withstand that increase and most stock type lifters cannot. Either way, no lifter, cam, or pushrod will take that abuse for very long. When you have 400+lbs of open pressure smashing metal parts together, repeatedly, things begin to wear and fail. Once the hardening on the lifter axle or cam lobe begins to scrub off, the cam or lifter will fail eventually.
Finally, you want the rocker to be strong in the right area: around the pushrod cup. This is where the pushrod sits, between the lifter and the rocker. Added material here does not affect MOI as much as over-the-nose weight, but it does add weight and thereby affect it to some degree. As with anything, there are trade-offs and the rocker still must be engineered correctly, but weight here is preferable to over the valve. If anything, weight on this side of the rocker, produces more strength and reliability in the entire valvetrain system. So be sure to check your rocker choice for added material in this area. Cam Lobes and Conclusion
The cam should have a fairly mild lobe, designed for endurance, RPMs, and longevity. That way, you’re able to build the valvetrain system as light as feasible, reducing the spring pressures and decreasing the friction and weight of the valvetrain. And valvetrain stability is the key to both power and reliability. Go with only as much spring as you need and nothing more. Look long and hard at beehive springs, the biggest pushrods you can fit, lightweight and strong rocker arms, and lifters that can take the abuse.
And combined with an endurance type lobe, you aren’t giving up much if any power due to the better valvetrain harmonics. Let the heads and the intake/exhaust do the work of making the motor an efficient airpump. Don’t overcam or put the nastiest lobes in there. You won’t see a faster car, but you’ll see one with more reliability issues.