(Welcome to Power Explained, a new multi-part series where I explain the tuning process and mechanics involved and how they affect your horsepower numbers)

Lets start with the most difficult part of this all. How to say dymanom..., no dyno-mo-meter, wait, no that's not right either. Dynamometer (Die-nah-mom-a-ter), but seriously, just call it a Dyno (Die-no), everyone knows what you are talking about.

Most people think that a dynos sole purpose is to prove to their friends that their Civic does in fact make 180 horsepower. While this is one of the things a dyno can do, it can be used for much,much more.

A dyno is a tool, just like a hammer, or a screwdriver, only way more complicated and not available at Harbor Freight (yet...). There are many types of dynos for many different purposes, from engine dynos to transmission dynos, each has its own purpose. The most commonly used dyno is a chassis dyno, where in a complete vehicle is placed on the dyno, and is used to measure, primarily, horsepower and torque as measured at the drive wheel(s).

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Chassis dynos come in all shapes and sizes, some are designed for commercial vehicles, others for emissions testing, many are used for tuning purposes in aftermarket performance shops. For the sake of this segment, we will be discussing the chassis dynos used in performance shops. There are two primary types of chassis dynos, inertia and load.

An inertia dyno uses a known mass being accelerated by the vehicle to calculate power and torque, while a load based dyno applies a measured force, usually via an eddy current brake (electro-magnetic resistance), against the rollers, and calculating torque and horsepower based off the force the differential applied by the vehicle.

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While both have their pros and cons, this segment will focus on inertia based dynos. As mass can not change with heat, or need to be re-calibrated from time to time, inertia based dynos are more likely to give easily repeatable results.

Modern dyno equipment can measure everything from air/fuel ratio to gathering the information from the on vehicle sensors. And when equipped with load control, anything from basic highway wind resistance to a full out hill climb can be simulated. This allows tuners access to a plethora of information, allowing them to tune your vehicle for a very specific purpose, and print it all out on a handy graph.

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Tune in next week for Horsepower: What it is and why your car doesn't make what you think it does.