dyno diffrences, taken from rickyb on mr2oc Options

[presure2]

here is some info that i think we could use here that i took from rickyb on the mr2 board about diffrent dynos:

As a tuner I often spend at least ten minutes explaining the different types of dynos and their application to my cutomers. Modern chassis dynamometers come in basically two flavors: intertial or braking. The Dynojet 248C is the current workhorse of the automotive chassis dyno industry and it is a pure intertial dyno. The power output of the engine is measured by determining how quickly the car can spin up a large rotating drum. The advantages of this setup are low cost and highly repeatable and accurate results even across different dynos. That means that you can take your car to any 248C across the country and at the same general elevation you should get very similar results. This is why discussion boards dismiss any dyno results except those produced on these dynos as being comparable to any other results. The downside of these dynos is that torque can only be measured as an effect of acceleration of the drum. This is a problem because both engines and drums have a maximum safety limit on how fast they can rotate before they can self-destruct or pose very potential safety issues. As a result, inertial dynos are good primarily for testing WOT power.

Brake dynos are a different beast. These dynos use a braking system of some sort and a device to measure actual instantaneous torque. The adjustable braking force is provided by either a water brake (basically a very inefficient water pump that turns engine output into instant hot water) or eddy current (a short-circuted electric generator that turns engine output into hot air). Many manufacturers make these including Mustang Dyno, Dynapack, Dyno Dynamics and Dynojet. Because these dynos can provide a predetermined amount of braking force equal to or just slightly greater or lower than engine output, they can be used to hold an engine at many different RPM and load points. This makes them ideal dynos for tuning not just at WOT but at many different load points. The downside of these dynos is that their torque measuring devices need to be calibrated regularly (not a difficult process) to keep them accurate across dynos and even on the same dyno over different periods of time.

Most brake dynos have practically zero inertial component, which makes it easy to reach a given RPM set point quickly. On these dynos you can take off in any gear. There are advantages to this in terms of being able to reach high RPM and load points quickly even on fairly wimpy engines. Some dynos such as the new Dynojet 224xLC have both an inertial and a braking component. The advantage to this is that they can more easily reach the low load, high RPM points that your engine can be in while you cruise on the highway. A good tuner can more easily and quickly reach and precisely tune more of your EMS map with one of these dynos.

Like with most everything else, all modern chassis dynos are good at what they were designed to do and sometimes can be passably used to do things that they weren't designed to do. If you plan to use a dyno, be very clear and specific in your mind about what you want to use it for before you decide on which one to use. If you want to publish results that you can brag about on this board, you will most likely want a Dynojet 248C. If you want to tune your EMS, you will be able to do that more precisely on a load holding dyno. In most cases, unless you are tuning the EMS yourself, it is best to choose the tuner and go with whatever he can do the best job with. If that is not a 248C, then you can always go find one of those after the car is properly tuned to find out how your car compares against some of the results posted on the public forums.