Home-made chassis dynamometer.




Do I need a dyno?

Some people, even the brightest engineers mind you, do not believe in dyno testing engines.  That's a fact.  At this point we'll leave behind the nay sayers and move on to the positive reasons for dyno testing.  Don't worry about proving the dyno point to someone who doesn't get it.  Just move on, knowing in your own mind you and tens of thousands of others have seen the light.  Dynamometers are tools. They are good for collecting data.  Not every type of dyno is perfect for every application, but as with any tool, when the right one is used the job becomes easier.   Use of a dynamometer does not guarantee an engine at its optimum state of tune, nor does having or using one guarantee that you will be able to tune out any anomalies that arrive in your power curve.  Some engines just by their nature (due to cam timing, port size and pipe length) may have a severe flat spot in the mid range that no amount of carburetor jetting or ignition timing can eliminate.  Using a dyno however, can reveal important information about what an engine is doing and display the engine's out put in a meaningful format.  It is the interpretation of that data that is important.  In many cases you don't even have to very experienced with a dynamometer chart to make good tuning choices. 

Some say they are not accurate.  Accuracy has little to do with it.  I could care less if the read outs were in torque, horsepower or pumpkins-per-fortnight.  All one absolutely requires is repeatability.  Repeatability, or lack thereof, lies mostly in the user.  Engines themselves need to reach a stabilizing temperature before their output becomes repeatable run to run.  Also chassis dynos put their own variability into the equation when we start to deal with tire side wall flex and heating, tire tread slippage on drive roller(s), drive line variability (o-ringed and grease filled chains operate in an efficiency zone based on temperature as do belt drives), etc.  The repeatability of a test can be verified by performing another run identical to the one previous.  Often a machine may need to be run through several dyno "pulls" before all these variables stabilize. These will appear as runs of increasing value.  Runs should be performed back to back until at least two to three identical pulls appear.  It is at this point that the tuning changes can commence and they nay sayers theories about repeatability are put to rest.


What is a chassis dynamometer?

A dynamometer tests the power of an engine or powertrain. It measures output shaft or wheel speed and, in some cases, torque and time. Apply laws of physics to that data and power output can be calculated. Modern dynos have computers to do the math and provide the results either on a computer monitor, in printed form or in a data file.

A chassis dynamometer accommodates an entire motorcycle and allows operation of its powertrain while the vehicle remains stationary. The motorcycle is attached to the dyno with tie-down devices and its drive wheels sit on a metal roller. The roller is connected to whatever measuring system the dyno uses to test drive wheel output.

The chassis dynamometer was developed in 1938 by Clayton Industries. It was termed a "hydrokinetic" dyno because it used a water brake to absorb power. Since then, chassis dynos have been built with water brakes, oil brakes, eddy-current brakes, generators and other devices which actively absorb power.

While brake-type chassis dynos are great pieces of equipment, most are expensive, a good part of which is the power absorption system and its controls. Another problem with some brake-type chassis dynos is they lack the accuracy and repeatability demanded by many performance-aftermarket manufacturers and tuners.

Dynojet Research of Belgrade, Montana, invented the "inertia" dynamometer in 1989 to test motorcycles. An inertia dyno differs from a brake dyno in several ways: 1) it has no active power absorption device 2) it's more accurate, 3) it's less expensive, 4) it's easier on the vehicles being tested and, 5) it's easier to use. Some of the technology that made an inertia dyno feasible was the personal computer's ability to make rapid computations.

Because the inertia dyno idea is so simple and cost-effective and Dynojet has had success marketing the concept, and other manufacturers have recently introduced similar products.


Data Acquisition for home-made dynamometers.

It is hard for me to imagine doing any sort of tuning now with out access to some sort of dynamometer.  Data acquisition is so low cost now, that anyone with a basic PC can pop on an external dynamometer data acquisition for less than $1000. Top of the line dynamometers from 10 years ago didn't have that capability and most today still don't.   This type of power in a personal computer can allow the average racer to gain a technological advantage over his competition.   Home-made dynos are a more viable option than they once were with the advent of low cost rapid accelerating data acquisition technology.

For example: SP1 can computerize your dynamometer for improved accuracy and time savings. You can watch "real time" gauges as you run the engine, make color torque and HP graphs and print them in color with a color printer, overlay unlimited graphs for comparisons, save runs for retrieval in the future, make reports and averages over most any RPM range and much more.

The manufacturer, Sportdevices has been doing dynamometer software since 1999. From a simple system recording just RPM/torque/HP up to a complete system recording fuel pressure, flow pressures, A/F ratio, 8 exhaust temperatures and more; Sportdevices can supply the complete package.



This site already assumes you don't need convincing of the viability of testing.  It will focus on the types of dynamometers from the old and simple to the new and complex to the new and simple yet again.  The information is provided to give an understanding of how dynos work and how one can use or perhaps construct a dyno of their own.   Dynos have been around since the construction of the first engine.  I would venture to guess they will be around as long as engines have a place in our society.  Understanding what makes them tick can make them an asset to any true motorsports enthusiast.




racingdevelopment.cjb.cc, Another project using Sportdevices.