Ford Mustang Performance Parts Test - Wheels Of Fortune

Horse Sense: Horsepower and torque can be mathematically equated. Torque equals horsepower times 5,252, divided by rpm, while horsepower equals torque times rpm, divided by 5,252. By this equation, horsepower and torque curves will cross at 5,252 rpm.

We rely on them whenever possible to quantify the results of parts we install. You likely do too. And, teamed with a knowledgeable operator and the right options, they can be a valuable tuning tool no matter whether you're fiddling with low-tech carb jetting or high-tech electronic tomfoolery to ward off meltdown after a high-boost blower installation.

We're talking about chassis dynamometers-those devilishly useful devices that have become so common in our high-performance Mustang world that we almost take them for granted. Because it reads at the drive wheels, a chassis dyno can be used to examine not only the effects of engine modifications, but also changes to drivetrain components, such as swapping trannies or even lubricating fluids. Around for decades in one form or another, the advent of powerful personal computers and other modern electronics and sensors have thankfully made the chassis dyno more common, accurate, functional, and operator-friendly than ever.

As with many aspects of technology, it's not imperative that we know how chassis dynos work in order to benefit from them, much as we don't need to know the recipe for beer to enjoy sipping a cold one. Just the same, we wondered how all that horsepower magically jumps from those rotating steel drums to the computer screen or printout. Is the transition accurate? Are all chassis dynos the same? As someone once sagely proclaimed, "Ignorance is a voluntary misfortune." Editor Turner suggested it was time I made myself more fortunate on the topic of dynos and shared that good fortune with anyone willing to listen-meaning you.

And so we bring you this little primer on chassis dynos. This will certainly not be an engineering-level discussion, and it is in no way intended to suggest that one model is better than another. We'll simply take a look at some of the basics of dyno operation and talk about a few of the various models we're most likely to cross paths with, from companies such as Dynojet Research, Mus-tang Dynamometer, SuperFlow, and Dynapack.

What Goes In Before the Name Goes On?
Peering into a dyno shop, all we might see are some steel rollers, or drums, either in the floor or up on an elevated stand, along with a PC, a monitor, a printer, and a hand-held controller for the operator while he sits in the test vehicle. These components are common to nearly all chassis dynos-except those from Dynapack, which don't use drums at all (more on this later). These drums can be of either small or large diameter, depending on manufacturer or model, but all are of carefully documented dimensions and mass-knowing their exact radius, circumference, and inertial mass is critical in the accurate calculation of power and torque. Generally speaking, the larger the drum diameter, the higher the road speed that can be simulated on the dyno. And we often see just the tip of the iceberg protruding from beneath the floor. Typical total drum weight is more than a ton.

It's what's in between the drums and the computer that varies from dyno to dyno. While all have some means of precisely measuring drum rotation speed, many have additional hardware to "load" the dyno beyond the inertial weight of the drums themselves. This divides the chassis dynos in our discussion into two basic categories: ones that function strictly by the inertia of the drums, and those that can, in one of various ways, be "loaded," meaning they have some method of "absorbing" power. The latter are more expensive and have testing capabilities beyond those of inertia-only models.

Each manufacturer has its own operating software-almost universally now in Windows format-that is used to take the raw data the dyno hardware is measuring and convert it to horsepower and torque figures and, in some cases, various other forms of performance data. Those figures can be plotted against corresponding points such as engine rpm and road speed, along with other readings if optioned accordingly.