When thinking about a V-8 performance engine it is easy to visualize our machines as a mechanical symphony working in perfect symmetrical harmony. Such an impression, however, fails to recognize that each of those individual cylinders may not be identical in their resources and their resultant mechanical contribution to the engine as a whole. One of the easiest examples of this reality is to visualize the variance in the induction tract. With the typical single four-barrel induction, the carb physically sits in the middle of the engine, putting it closer to the inner cylinders 3, 5, 4, and 6, than it is to cylinders 1, 7, 2, and 8 (GM and Mopar numbering system). What results is a different flow path, and given the realities of intake manifold design, differing runner length. This might seem like a minor inconsistency to us. To the engine, runner length plays a major role in how the airflow turns into the cylinder. On top of this incongruity, add in the effects of wet flow of the typical intake manifold, and you’ll find that characteristically there are significant variations in air/fuel ratio when considering the inner cylinders with a more direct flow path, and their outboard brethren.
Our individual cylinder lambda monitoring was via electronics from Daytona Sensors. The sy
While we might be comforted by examining the running mixture of our V-8 powerplants by virtue of today’s sophisticated lambda sensor systems, bear in mind that the reading you get from a single oxygen sensor in the collector represents an average of all the cylinders in a given bank. In reality, there is a variance in air/fuel ratios from cylinder to cylinder, and the greater the delta here, the more compromised the engine will be with any given tune. The optimal mixture for maximum power will coincide with the point at which that average is actually working as the best compromise among the cylinders comprising the reading. Obviously, the tighter we can keep the air/fuel ratio variance, the more efficient the engine, and the greater the potential for optimal power production.
The 4-Pattern cam timing strategy is based upon the varied intake flow paths typical of a
Given the realities of the differing induction characteristics of a typical V-8 engine, it is a fallacy to believe that other interrelated operating requirements would remain identical from cylinder to cylinder. This premise naturally brings us to the camming requirements of the engine. The key question to be addressed here is whether a cam timing strategy can be employed that will help compensate for the variance peculiar to the V-8 induction tract. The idea here is nothing new, and at the upper levels of professional racing, such aspects of camshaft design have been experimented with for decades. Subtle variations in specifications designed to compensate for irregularities between cylinders have been employed in venues such as NASCAR, where every horsepower counts. At COMP Cams, the idea was to extend this concept to the street/strip level enthusiast with their new 4-Pattern cams.
Our baseline XR294HR cam is part of COMP’s Xtreme Energy line of hydraulic rollers, long t
Our test engine was based upon the Dart SHP short-block, which has provisions for all of t
The Dart block also features lifter bores and valley bosses designed to accept the standar
Strategically, what the 4-Pattern cam does is vary the cam timing for the inside cylinders versus the outer cylinders. The objective of this strategy is to better use the flow dynamics and induction length of the cylinders with the aim of higher output. The outside cylinders are given a slight increase in duration and intake lift, while at the same time the lobe separation angle for the outside cylinders is increased. The result is the intake valve closes later for the outside cylinders, while the exhaust opens earlier. With this strategy, the intake opening and exhaust closing for each cylinder remains constant keeping the overlap the same. The objective is to capture more air/fuel mixture in the deprived outer cylinders, boosting their contribution to overall engine output.
While on the surface the timing strategy is the most significant quality of these new camshafts, the lobe profiles themselves are improved. Notably, the lift for a given duration level has been increased, making the 4-Pattern cams more aggressive than the former state-of-the-art Xtreme Energy lobes. While the faster lift action is readily apparent from the basic lobe specification numbers, the profiles take advantage of the latest technology in lobe design to push the standards of lobe stability to new levels. Extensive Spintron testing at COMP has qualified these lobe profiles to exceed the rpm capabilities of previous designs. Theoretical power is one thing, but once stability is compromised, power production is over with.