Jim had a storied career in the automotive performance industry, beginning in a variety of editorial roles at Hot Rod magazine. For 19 years he served as Vice President/R&D for Edelbrock Corporation where he oversaw the design of automotive induction and exhaust systems, camshaft/valvetrain components, and cylinder head development, while having extensive interfacing with exhaust emissions controls regulatory agencies, including the U.S. EPA and CARB. Over his 42 years of experience, he has worked for and consulted with some of the biggest names in the automotive industry.
SEMA's "Person of the Year" Award recipient in 1985, McFarland is the author of over 300 automotive technical/feature articles including SAE Papers, general performance automotive publications dealing with the motorsports, RV, outdoor and truck markets. He has won numerous awards, is a member of the SEMA, International Drag Racing and Hot Rod Magazine Halls of Fame, and was elected to "Fellow" grade of the Society of Automotive Engineers' Institute for the Advancement of Engineering.
Charles holds two masters' degrees in mechanical engineering with his primary field of study in thermo-fluid science. He has worked in engine and fuels research at both the OEM and supplier level and has completed leading-edge work in the mathematical modeling of high performance four stroke spark-ignited engines. In Motorsports, he has contributed to championships in IMSA, NHRA, and NASCAR Nextel Cup as well as two Daytona 500s. He most recently served as Technical Director for Dale Earnhardt Inc.'s Engine Department.
Now based in Europe and working as a consultant in Formula One and Moto-GP, Mr. Jenckes has authored articles and technical papers on a wide range of engine topics from combustion and emissions to the use of CAE (Computer Aided Engineering) in engine development. He has received numerous awards for his work and presentations from the Society for Automotive Engineers (SAE).
Photo by Jeff Huneycutt
Over time, a considerable amount of material has been written about the merits of horsepower in a racecar. And, likely in an equal period, the value of optimizing power has also been banded about. Of the points advanced in Part I of this series, one we should focus on is where in the engine's speed range power occurs and how this relates to on-track performance as it pertains to final-drive gearing. Although power gains in a two-stroke-cycle engine are linked to an increase in peak rpm, a measure of this logic can be applied to four-stroke-cycle powerplants. But first, let's have a clear understanding of torque and horsepower.
By definition, torque is the measure of a twisting force, absent motion. Grasp a locked door-knob, apply a twisting force and motion (torque) only impends, but it's measureable. Suddenly, unlock the knob and the applied twisting force causes motion, measured as horsepower. Simply stated, horsepower is torque acting over time. In other words, torque is an "independent variable," and horsepower is a "dependent" variable, the amount of which is based on torque input and rpm. Conventional wisdom suggests torque accelerates a racecar, horsepower makes it fast. So, the placement and amount of torque in an engine's speed range becomes critically important, particularly when proper gear ratios are selected-as pointed out in the text of Part I in this series.
Years ago, during the development of multiple intake manifold designs, we developed design tools that enabled torque curves to be "shaped" in a fashion that provided power where it was needed, not relative to peak numbers. These techniques proved quite valuable for applications that included short- and medium-length circle tracks where corner exit speed (torque) was critical and did not relate to peak power. Plus, the ability of an engine to accelerate through its speed range (some have called this "transient" horsepower) adds to the benefit of corner exit speeds, for example.
However, as track length increases and throttle on-time correspondingly grows, a reliance on horsepower and higher rpm becomes of value. Note the fact that peak super-speedway engine rpm is now in excess of 9,400, whereas only a few years ago this cap was in the low-to-mid 8,000s. Much of these recent gains in engine speed have come from higher rpm-capable valve trains. As the series unfolds, we'll be talking more about this issue and how it relates to weekend racers.
Meanwhile, understand that peak horsepower numbers aren't the singular goal in building a successful circle track engine. Hopefully, this evolving series will help you understand the logic and reasoning in support of that statement.