When this Series of stories began, its stated objective was to meld Cup engine practices with what might be applied to weekly racers, certainly in terms of affordability and doability. And, as we button up the subject, it seems worthwhile to spend a little time discussing some of the better ways to evaluate a given parts combination, notably on an engine dynamometer. In so doing, let's examine how the use of such test equipment has transitioned to today's methods and technology, and discuss some down-to-earth techniques for sensible data evaluation.
Most all of us in this industry/sport recall the early purpose of engine dynamometers. Essentially, by their very nature, they were used to simply measure brake torque; data that was then converted mathematically on a time-rate basis into brake horsepower. Some of the first engine dynos to find their way into motorsports were iterations of dynos that either came from the OEM or were built by persons who had experience in that environment. Early dynos at Holman-Moody's and Smokey's come immediately to mind.
But regardless of their origin or capabilities, the fundamental goal of an engine dyno was to measure brake horsepower. At this point, it hadn't yet become evident to dyno users that the use of in-car pieces (headers, ignition systems, cooling systems, etc.) on the test stand would be a logical step toward the need for linking engine testing with on-track performance. The importance of this fact was brought solidly home to me in the mid-'70s when sorting out some cylinder-to-cylinder mixture distribution fixes in a now bygone "Smokey Ram" intake manifold. Distribution fixes Smokey had determined on the dyno barely resembled what were required on the track.
Long before Land & Sea's DYNOmite Dynamometer, Smokey Yunick "drove" a dyno of his own. Ph
In addition, the rather immobile state in which an engine on a test stand operated didn't duplicate the dynamics (including air movement, spark, and fuel calibration requirements) found on the track. So it seemed something that might be common to both environments would be a useful next step. Fortunately, we landed on the commonality of "combustion efficiency" between dyno and track as one possibility.
I will not take credit for what you will now read. It came from a now-departed good friend who was deeply involved testing all manner of engines at the Champion dyno shop in Long Beach, California, circa 1971. On one occasion, he happened to be doing some "weekend testing" at the Edelbrock facility and I was there helping him. What immediately got my attention was the fact he was only recording brake horsepower (along with fuel flow) for his calculations of brake specific fuel consumption (BSFC). He had no apparent concern for how much power was being made, beyond use of this information.
If memory serves, he ran a series of tests through which only spark timing and fuel enrichment were changed. When he'd completed this exercise, he was finished. So, flushed with curiosity, I asked him to elaborate on why BSFC was so important to him. Paraphrasing his response, it went something like this: "What we're trying to do is an efficient job of converting fuel into heat (power). For any given package of hard parts, unless you start swapping or modifying components, the only meaningful adjustments you can make are to spark and fuel. Once you've adjusted these to the point of minimum BSFC, without an attending loss in power, there's nothing else you can do. Combustion efficiency has been maximized when BSFC, under the conditions I just described, is minimized. And when you get to that stage, you can then observe how much power you're making."
In all honesty, during the next thirty years of engine testing, I have found this approach to be the singularly most valuable technique I've ever found for evaluating engines on a test stand, aside from certain specific design or performance objectives and some supporting testing techniques.