Dynamometers: interview with Dyno Dynamics owner Chris Hodges 

First of all maybe you could say how does company Dyno Dynamics borne and began developing dynamometers?

Chris Hodges: My previous business Dynomotive was the leading workshop for quality work and accurate diagnosis in Melbourne, Victoria. At Dynomotive we used an eddy current dynamometer. It had some shortcomings but did a fair job. We could do things in five minutes that took five hours on the water brake and could never be done on an inertia dyno. People came from all over Victoria and interstate (even some from Perth over 3,000 km away in Western Australia) to get their cars (and trucks) “dyno tuned”. In Australia, water ski boats powered by big with five or six litre V8 engines are common. After experiencing the difference the “dyno” made to their cars, a lot of my customers wanted us to “dyno” their inboard boats as well. Well that was a problem. You can’t fix what you can’t test and diagnose! We couldn’t even road test a boat without damaging the prop and scratching the road!! We needed a boat dyno!

How did you go about making a boat dyno?

With the help of my (now) business partner Peter Humphris (fitter, turner, toolmaker, mechanical genius), we made a crude dynamometer that connected to the propeller shaft. A friend, Alan Oxenbould (electronic genius) made the electronic control system. It sounds easy but it took us several years to get it working properly.

It turns out, that if you join a V8 inside the boat, to a big retarder outside the boat, via a couple of yards of thin (1”) stainless steel shaft, give it a foot-full at five and a half grand, make it cough, without breaking anything or tying shafts in a knot, you have invented one hell-of-a dyno control system. We boat “dyno tuned” at night, and dyno tuned cars during the day. Because the boat dyno control system was so good, we decided to go into the dyno control system business.

Also how does it happened, that “Dyno Dynamics” in lot cases became a dyno standrat (company Dyno Dynamics in most cases is mentioned with a very big respect)?

I think that the main reason that Dyno Dynamics dynamometers have become the standard is because they have been designed by people who know how to use a dyno , rather than from the point of view of a design office. Peter, Alan and myself were very committed to making the best dynamometer in the world. In this we have been very successful. We have developed a very advanced yet simple design of roller chassis. The obvious things like roller design, vibration free beds, and hi traction roller surface have been designed to make the job of the dyno technician as easy and accurate as possible. The electronics we designed provide a very stable control systems, very steady readings and very high accuracy and repeatability.

Here we come to very interesting collision about chassis inertia dyno versus chassis loading dyno. Simple question which type of dynamometers is better for tuning cars? Or maybe in what cases should be used inertia or loading? Is it possible to tune car at partial throttle using inertia dyno?

Before answering that question let’s look at the main difference between an inertia dyno and a Dyno Dynamics eddy current dynamometer:

An inertia dyno has a very heavy roller(s) and a speed measurement system. The car is run at full throttle. The more power the car has the quicker it can accelerate the heavy roller. Knowing the inertia of the roller and the acceleration it’s a simple calculation to obtain power.

A Dyno Dynamics eddy current dynamometer has very light weight rollers. It also has a speed measurement system. In addition the Dyno Dynamics has an electromagnetic retarder that apply a load to the rollers. This load is adjustable and it works at steady speed as well as when accelerating. The dyno operator (technician) can vary the load from almost zero to very large. Knowing the inertia of the rollers), the acceleration, and the load applied by the retarder it’s a simple calculation to obtain power.

OK, so what are the main differences from the motorist point of view?

An inertia dyno cannot apply load unless the vehicle is accelerating. This makes it impossible to test a car on a level road at steady speed on flat roads or up hill, or slowing down due to hills etc.

A Dyno Dynamics dynamometer can easily test a car on a level road at steady speed on flat roads or up hill, or slowing down due to hills etc. A Dyno Dynamics dynamometer can easily hold the vehicle at a say 50% throttle and 2,500 RPM while investigating a misfire that occurs under these conditions.

Mapping the vehicles fuel and ignition computer is part of tuning any performance vehicle. How does an inertia dyno compare with an eddy current dyno?

In it simplest form, “mapping” a modern fuel injection computer involves:

• holding the engine at a particular RPM point (say 3,000 RPM)

• holding the throttle at a particular position (say 90% throttle)

• observe Air:Fuel ratio

• power

and adjusting fuel and timing to achieve best results. This process is repeated at a large number of RPM points and throttle openings. when mapping is complete, the engine will have optimum ignition timing and fuelling at all points in it’s operating range from idle through to max power. When steady mapping is complete, mapping whilst accelerating can be performed.

Does this mean that mapping at full throttle is possible on an inertia dyno, but an eddy current dyno is required for mapping the entire engine range?

Mapping at wide open throttle is possible on an inertia dyno in a limited way. For example, lets consider full throttle testing two cars with the same 150 HP engine. One car weighs 2,000 kg, the second car weighs 3,000 kg. On the road the heavier car will accelerate much slower than the lighter car.

• On an inertia dyno both cars will accelerate at the same rate.

• On a Dyno Dynamics dynamometer the operator can choose the rate (or let the software calculate the rate).

The rate of acceleration affects not only the engines requirement for fuel etc, but also combustion chamber temperatures vary considerably with acceleration and time under load. These variances required different mapping values.

As for atmospheric engines it seems clear, but what about forced induction? Is it safe to tune forced induction car on chassis loading dyno? Another side, will inertia dyno create enough resistance for engine to fully boost and produce maximum power?

Accurate and repeatable dyno test results depend on accurately simulating conditions. With forced induction engines this is even more important. For example, a Dyno Dynamics dynamometer enables the operator to stabilise conditions prior to each graph test. If the engine is simply run to the desired starting speed, than given a foot full (sorry, wide open throttle suddenly applied), then conditions at the start of the test will vary and so test results will vary. Turbo lag is a very important factor when testing turbo engines. For accurate results the acceleration rate during graphing is critical. Inertia only dynos have no means of stabilisation at the start, nor controlling acceleration during the test.

I found what your company has established a “Code of practice”, so you claim total honest between your tuning specialist and clients? Is this possible using dyno software to falsificate dyno run results and fool client?

It is possible to fool the client by many means. Even something as simple as using full throttle or nearly full throttle will affect results. Dyno Dynamics Shootout software rules out cheating with software; the Code of Practise and other things rule out other forms of cheating due to the operator lack of honesty.