To go along with a hot cam...
To go along with a hot cam combination, a valvetrain upgrade is advisable; with anything but a hydraulic, it's mandatory. The aftermarket has us Mopar guys covered with many quality choices, such as these affordable Crane roller rockers we used on a W-2- equipped small-block.
A solid lifter is fixed, so there is no compensating factor. Solid rollers are the top choice in racing since they maintain the benefits of a solid follower while the roller allows radical cam-lobe profiles. Solid rollers reduce friction where the lifter meets the cam, allowing much higher valvespring pressures than a flat tappet could endure.
Cam size is generally given as lift and duration. Lift is the amount the travel of the cam lifts the valve off the valve seat, while duration is a measure of the length of time a valve remains open in degrees of crankshaft rotation. When rating duration, cam manufacturers have traditionally played games using different start and stop reference points.
A standard was set in the industry to rate cams by duration at .050-inch tappet rise. This means the open duration is measured from the time the lifter moves up .050 inch on opening until it reaches .050 inch from closing. This is often referred to as duration at 50. This allows for more accurate manufacturer comparison of duration figures. Aftermarket cams are typically more aggressive in their action than a production camshaft, and the valvesprings almost always need to be changed. Follow the advice of the cam supplier for springs to match the cam and rpm range. Along with the springs, the retainers and locks (keepers) are often changed, either to fit the spring or to enhance reliability or rpm potential.
Balancing starts with weight-matching...
Balancing starts with weight-matching to get a weight spec for the internal engine components. Then, the effective weight-bob weight-is calculated.
The rest of the valvetrain needs to be matched to the requirements of the camshaft. Stock hydraulic-cammed big- and small-block Mopar engines used stamped-steel rocker arms and solid-steel pushrods from the factory. These work in mild hydraulic cam applications, but otherwise, the valvetrain needs upgrading. A solid cam needs a provision for valvetrain adjustment, so a rocker and matching pushrod change is a given. A hydraulic cam can also benefit from an adjustable valvetrain, allowing the depth of the pushrod's engagement in the lifter's hydraulic mechanism (the lifter preload) to be set for optimal performance. Stock big- and small-block rockers carry a design ratio of 1.5:1, meaning the valve is opened 1.5 times as much as the cam lifts the lifter. Aftermarket rockers can be acquired in higher ratios, such as 1.6:1 or more.
Engine Rebuild Basics: Part IIQuench Combustion
Selecting a piston that comes up even with the deck at TDC (typically with minor block decking) and using a standard .040-inch-thick gasket will be beneficial if used with a closed-chamber head. This tight clearance between the piston and closed deck of the head provides what's referred to as the quench effect, which adds combustion efficiency. Quench translates to more torque and better detonation tolerance, making the goal of an effective quench clearance worth considering when selecting pistons.
While a closed-chamber head naturally lends itself to a quench configuration, most Mopar engines used open-chamber heads. For these engines, pistons with a kick-up to provide a quench effect in open-chamber heads are available from many manufacturers. Be aware, however, that custom machining is required to make the most from the combination of a kick-up quench-dome piston and an open-chamber head. It may be cheaper and less hassle in many cases to buy an aftermarket closed-chamber head and use a flat-top piston.
There are a number of ways...
There are a number of ways to file the endgaps, from hand files to special electronic machines with indexing fixtures. A handy and relatively inexpensive filing wheel like this one from Summit Racing makes the job quick and easy with practice.
The other half of the quench...
The other half of the quench equation is the head. This Mopar Performance big-block head is a closed-chamber design, and this flat portion of the head will end up .040 inch from the piston at TDC, producing combustion-enhancing effects. An open-chamber head, like the stocker on the right, has a recess in the quench area and will need a kick-up quench pad to achieve a similar result. This involves precision machining to the head, piston, or both to optimize.