What do Dynos do.

The principal of what dynos are for is pretty basic, they measure the rotational speed, power output and tourque of any kind of engine, though in the modern age they have other uses too such as measuring Air Fuel ratios for tuning both carburetted and EFI systems.

There are two main types of dyno, the engine dyno, which is generally driven directly from the engine and the chassis dyno which does it’s work from the drive wheels, hence it’s name, and so takes into account the power output of entire driveline. Chassis dynos are the most common dynos to be found being used by ATV and motorcycle tuners here in Australia as they generally off the convenience of being able to ride straight on and do your testing without any special adapters other than maybe a change of tyres.

Out of this then there are many different sub-designs of dyno, once again though there are two main dyno designs in use locally, the intertia dyno and the eddy current dyno.

Inertia Dyno’s

An inertia chassis dyno basically consists of two big heavy drums on an axle that are then connected to a computer via a speed sensor. Horsepower is determined by measuring the maximum rotational speed of the drums and the time taken for the drums to get to that speed coupled with the RPM of the engine. The computer then extrapolates the tourque figure from these readings. To add consistency to the readings there are also sensors for air temperature and density as well as air/fuel ratios in the exhaust gas. The dyno’s software factors all of the data from these sensors to help give consistent horsepower readouts.

Inertia dyno runs are generally done in 3^rd or 4^th gear and starting from just above idle the throttle is then opened fully until the engine hits it’s rev limit. The up side of this is that you can do many runs quickly as the process of each run takes only seconds, the down side is that you are only really measuring at one throttle position, wide open.

Eddy Current Dyno’s

This type of dyno is generally accepted as the best tuning engine tuning dyno around, the eddy current type dyno can present a measurable force for the engine to push against. This is achieved via a system of rotating and static electromagnets which, when powered, produce the resistance load to the engine. What this means in real world terms is that you can measure torque,power and air/fuel ration at any throttle position which makes for a handy tool for EFI remapping and carburettor tuning both. Also because of the ability to vary the load on the engine it means that it is easier to replicate real world conditions in the workshop and therefore tune out flat spots in the power delivery

Results

Power figures will vary from dyno to dyno, even two different dynos made by the same manufacturer will give different readings for the same engine depening on the operator and the calibration of the machine. This means it is best to try to get all your dyno testing done on the same machine for accurate results.

The results that everyone wants to see however are how much power their engine makes after modification. The Best process for this is to get your ATV tested before and (obviously) after the modifications to best see the differences in power output.

Very Simple Image Gallery:
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