Power Explained: Dynamometers

"CAR_IS_MI" (car-is-mi) 01/24/2014 at 01:58 • Filed to: Power Explained, Dyno, Dynamometer

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(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).

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.

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.

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

Arch Duke Maxyenko, Shit Talk Extraordinaire > CAR_IS_MI 01/24/2014 at 10:05

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Horsepower a mathematical equation based on torque multiplied by the rpm divided by a constant.

PS9 > Arch Duke Maxyenko, Shit Talk Extraordinaire 01/24/2014 at 10:06

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Fickin' spoiler alert, you no good dirty spoiler!!

Arch Duke Maxyenko, Shit Talk Extraordinaire > PS9 01/24/2014 at 10:10

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Sinanigans > CAR_IS_MI 01/24/2014 at 10:12

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Interesting piece. I was hoping for a little more detail but good info. Just out of curiosity, can a tuner set up a dyno to inflate the data from a car? For example, if a car read 180whp on the dyno as a baseline figure, could a tuner say that his tune increases whp to 200whp in attempts to sell his services?

roflcopter > Arch Duke Maxyenko, Shit Talk Extraordinaire 01/24/2014 at 10:35

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It's a function not an equation....

I'll show myself out.

Arch Duke Maxyenko, Shit Talk Extraordinaire > roflcopter 01/24/2014 at 10:37

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roflcopter > CAR_IS_MI 01/24/2014 at 10:37

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"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)."

I know you cleared it up later, kind of, but I gotta say it. You can't measure horsepower dammit!

roflcopter > Arch Duke Maxyenko, Shit Talk Extraordinaire 01/24/2014 at 10:41

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Yep, that's a nice function you got there.

Arch Duke Maxyenko, Shit Talk Extraordinaire > roflcopter 01/24/2014 at 10:49

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CAR_IS_MI > roflcopter 01/24/2014 at 10:49

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Horsepower ( hp ) is the name of several units of measurement of power , the rate at which work is done.

Come again?

roflcopter > CAR_IS_MI 01/24/2014 at 10:55

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It can be calculated from known torque at a particular rpm, but not directly measured.

CAR_IS_MI > Sinanigans 01/24/2014 at 11:00

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There will be much more, this is just an intro, and it will all fit together, I just didn't feel like posting a book.

As per inflating numbers, yes and no. Depending on which manufacturers dyno, they could. There is a video on youtube of a shop that has a dyno where you can configure EVERYTHING, including drum mass. In the video they dyno a stock Nissan Sentra and it puts down 180hp or something like that. then the "make upgrades" [read: change parameters] and the car is putting down 5xx hp. They make one more final "adjustment" and the car puts down something ridiculous like 1,xxx hp.

There are also some shops that will give you your readout in STD correction, which was the old US standard, currently used by sprint car teams and a few other race series. The current US standard is SAE. the difference between the two is minimal, but generally the STD will show slightly higher.

wabbastang > Sinanigans 01/24/2014 at 11:02

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Yes to a degree, by manipulating the weather correction factor if it has that feature, not all do. Aside from that as long as the machine is in good working order, there really isn't a way to make it generate what you want to see. And yes, I own a dyno, a fancy one, I'm not making this up based on what my brother's friend said who has a 180hp civic and almost dyno'd it once. The easiest way is by adjusting atmospheric pressure. The result that will have on numbers varies based on a lot of other factors, it can make no difference or a huge difference. It's basically all-around bad practice though, as you'll get a reputation for high/false numbers, and then have to live up to that in the real world. Most guys that build/tune a car on a dyno will probably end up running on another dyno at some point it seems like, dyno day or whatever, and then would see a lot different numbers. No operator that can see past the end of their nose would do that intentionally; I say that because the fancier a machine gets the more factors and equipment comes into play that you rely on for consistency. They also produce more reliable and consistent information.

CAR_IS_MI > roflcopter 01/24/2014 at 11:05

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Okay, Ill give you that, but if I pulled an Arch Duke and said the formula is [MATH], most people would look at me funny (not that they don't do that already anyways). The simplest way is to say measured, but you are correct, the term I should have used is calculated.

wabbastang > roflcopter 01/24/2014 at 11:05

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I get what you are saying, but sure you do, any measurement is based off an equation that translates raw data of SOME sort. A dyno's analog load cell sensor doesn't output it's data in ft/lbs :P

But yes, it is starting with a torque measurement and calculating the horsepower.

roflcopter > wabbastang 01/24/2014 at 11:19

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It's the difference between measuring length and finding area... You can use a ruler to do one, but you have to calculate the other.

Casper > roflcopter 01/24/2014 at 11:27

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You technically could measure work done over time directly... it just wouldn't be done using a dynamometer. For instance if you had some contraption as the original idea of a horsepower was derived in which work was done (lifting a weight off the ground) and measured the time it took to complete said task, compared it to the time it took a horse to do the same task, and devised a value, it would technically be a measurement of work done over time rather than torque.

I don't think I would trust that method of measurement anymore than other dyno charts on the internet, but it would be fun seeing people constantly checking calibration with different breeds of horse...

Vince-The Roadside Mechanic > CAR_IS_MI 03/25/2014 at 20:20

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hi dynamo is in my name