Stud or Not?
Maintaining a seal at the junction of the cylinder head and block becomes more critical as engine power and cylinder pressure increase. While a plain stock replacement gasket and the used stock bolts will get the job done on a low-buck overhaul, stresses in a performance engine require a more serious effort. Of course, quality gaskets and properly machined mating surfaces are a must, but the fasteners play a key role. All the clamping loads are imparted by the fasteners and need to be up to the job. High-tensile fasteners directly increase the loading, and that’s a real plus. Upgrading to studs gives more even loading of the clamping forces and also eliminates wear and tear in the block threads as the fastener is torqued. Studs will make service a little more difficult, since the head will now have to be pulled clear of the fasteners, but when the pressure is on, a set of studs is a much more secure choice.
A properly functioning valvetrain is key to reaching the rpm and power potential of an engine. Many individual items comprise the valve operating system, but the spring is the one part that makes the valvetrain follow the cam. If the spring isn’t getting the job done, power will always be curbed. Springs have to operate at the required load, and that load varies with the amount the spring is compressed. How much load is increased as the spring is compressed is a function of the spring rate, and that is a constant, given in pounds per inch. We regularly see springs that are listed as a recommendation for a given cam, but installing the recommended spring does not ensure success. Remember, the spring’s load is directly a function of how much it is compressed. To make sure the load the spring delivers is within the correct range, always check the installed height, and then test the spring at that height to give the closed load. Next, additionally compress the spring by the amount of valve lift, and you’ll get the open load number. This is what the engine will actually see in operation, and it can be adjusted with shims or different retainers or keepers.
Hardened lash caps are nothing new, though their use in performance engine builds seems to have fallen out of favor in recent years. The lash cap adds an extremely hard and wear-resistant surface to the valve tip while providing a substantial increase in contact area. These are reasons enough to consider lash caps, especially with aggressive solid flat-tappet or roller cams. We often add lash caps as a convenient means of adding a small amount of valve length, which can help valvetrain geometry in high-lift cam applications. Some things to be careful about when using lash caps include ensuring that the cap does not contact the valve keepers—a mistake that can cause a dropped valve. Adding screens to the lifter valley returns is good insurance against the lash caps or other components entering the crankcase in the event of a valvetrain failure.
Piston deck height refers to the height of the piston relative to the engine block’s decks. A negative deck height means the piston is below the surface of the deck at TDC, while a positive deck means it is above. A piston is said to be at zero deck when the piston is exactly at deck height at TDC. Why is this important? The deck height of the piston plays a major part in the clearance volume of the assembled engine, one of the factors that determines the engine’s compression ratio. The deck height, along with the head gasket thickness, combines to produce the piston-to-head clearance, which dictates the squish-quench characteristics of the engine. A tight piston-to-deck clearance improves combustion efficiency and power while adding to the detonation tolerance of the assembled engine. These clearances are critical to engine performance and longevity, so careful measurement is essential. A good-quality deck bridge and dial indicator are the tools of the trade for determining piston deck height.
When setting up an induction, the most common air inlet system is just a wide-open, 14-inch air cleaner sitting above the intake manifold. We can see why this arrangement is so popular, since it looks great and takes virtually no effort to install. However, breathing hot underhood air is not the fast track to high power. Air density decreases with temperature, and less air means less power. Hotter air is also more likely to detonate, unnecessarily limiting maximum cylinder pressure and power. These days we can’t think of a single production vehicle without some form of cool-air induction. Cold-air induction can be achieved in a variety of ways, including anything from a hoodscoop to some creative homemade duct work. This effective system was built from a stock air cleaner, modified with a large, 4-inch snorkel.
Braced for Strength
While a shaft-mounted rocker system is generally considered the ultimate setup, for budget-conscious performance fans, stud-mounted rockers definitely offer a price advantage. The problem with stud-mounted rockers is that all the load is concentrated at the base of the stud, leaving the rocker unsupported and simply hanging in the breeze at the working end. While this isn’t the most advantaged arrangement from an engineering standpoint, the stud-mounted system is simple, inexpensive, and effective in milder applications. A midrange improvement for any stud-mounted system is adding a stud girdle. The stud girdle ties in the upper part of each stud, essentially spreading the load to the adjacent studs. This reduces the stress each individual stud sees, improving durability and making failure less likely. While we wouldn’t recommend a stud-mounted rocker system in an all-out race engine, we wouldn’t hesitate to add a stud girdle to a performance engine that uses stud-mounted rockers.