Power Trends
One of the products of the Engine Masters Challenge is something not as obvious as the nut-and-bolt creations of our engine builders, but is perhaps even more valuable than the metal. What I'm referring to here is information. In a highly competitive event like the EMC, we see all sorts of modifications made in an effort to edge out the competition. It's not always easy to single out the virtue of a single modification among the many made to a competition engine, but careful observation of what the builders are doing provides a wealth of insight.
We can look at any system in the engine and see how the parts selection and execution is approached by the front-running builders. Some solid trends seem to emerge with a little scrutiny. We can look at these trends and ideas and apply some of the same thinking to improve our own engine builds. In the past, the test rpm range in the Challenge has begun at a very low 2,500 rpm, and the limit of the test was a moderate 6,500 rpm. The rpm range plays a critical part in the builders' problem solving, since winning at the event requires making the most power possible over the entire rpm range. Naturally, the operating range significantly influences the build, and with the changes in store for 2009, we can expect to see some changes from the combinations that have proved successful in the past. Here are some of my personal observations from previous events, noting some of the engine building tricks that really seemed to work in a few selected areas.
Camshaft & Valvetrain
It was interesting to see the variations in camshaft theory played out in the Challenge, and trying to pick trends that seemed to work. A critical aspect for the builders was making power at the bottom of the curve, while maintaining enough steam to make a number at the top end. It was almost universal to see the builder striving to maximize lift. This commodity was limited by the rules requirement for a flat-tappet cam, and the inherent limitation on spring load as a result. Still, we witnessed very high lifts, often resulting from the use of very high rocker ratios. We also noted that the lobe separation angle tended to be very narrow, which would encourage a very strong torque rise, with moderate duration and advanced installed centerlines, both aimed at preserving the lower end of the torque curve.
Heads
There is no doubt that the cylinder heads have a key role in a winning engine, and here we saw the trend was toward efficiency rather than outright size. The limited rpm range and the need to make strong power down low play a heavy role in influencing the trend here. A smaller port tends to improve velocity, while overall flow cannot be neglected in order to make a big number at the top end. Relatively large valve sizes seemed to prevail, as did engine types with canted valves for improved flow.
Carbs & Induction
Looking at the front runners, the overwhelming trend was toward single-plane designs. Although a two-plane generally offers improved torque down low, the single-plane seemed to be favored when considering the entire curve. We noted that the leading engines all featured fairly extensive port work, and like the cylinder heads, the aim seemed to be to maximize flow while keeping within a moderate dimension. We had many builders indicate that the sizing of the manifold runners was a major part of the engine development effort.