Tuesday, January 24, 2012

Tech: Dynos, the useful tuning tools for cars

A Nissan 350Z is set to spin the rollers on a dyno.
Spend enough time at a race track, car meet or even with a couple car enthusiasts and you are bound to hear the word "dyno" come up.  This isn't in reference to the bygone era of our reptilian oil suppliers' fossilized bones, but rather to a device which many people use to see how much horsepower and torque their vehicle is putting down to the drive wheels.  Dyno is the short term for dynamometer.  Today's discussion will give you an overview of the basics of dynos and their usefulness. 

In the car tuning industry, the 2 main types of dynos being used are:  Engine and Chassis.  An engine dyno measures horsepower and torque without any of the drivetrain hooked up to the engine.  This includes the transmission, differential, axles, and sometimes accessories like the alternator and power steering pump.  Engine dynos measure the horsepower coming directly from the flywheel.  When a person quotes numbers from an engine dyno, they are generally much higher than those measured from a chassis dyno.  Manufacturers usually quote their engines in terms of brake horsepower (Bhp) which is close to what an engine dyno will measure.

An engine dyno looks similar to the above setup. 

This is an engine being tested on an engine dyno. 

Chassis dynos are much more commonly used today in the car tuning industry.  They can be one of a number of different types.  A couple dynos measure power by attaching to the hubs of a car and a hydraulic load can be placed on the car, which the vehicle must overcome.  A popular version of this dyno is the Dynapack dyno. 

Other chassis dynos use rollers that a vehicle must spin.  Simply put, the time it takes the car to spin the rollers is then calculated into horsepower and torque figures.  Popular versions of these dynos are the Mustang and Dynojet models.  Since the vehicle is strapped down to a dyno, drivetrain losses through the transmission, axles, etc. are accounted for and the result is a lower number than an engine dyno produces.

Also, since the losses are accounted for in both the hub mount and roller dynos, the power figures produced by them are commonly accepted as the closest number to the actual power a vehicle is producing.  Beware that unscrupulous individuals can skew the input into a dyno to produce unrealistic or inflated power figures.

Dynos may be fixed units built into a shop, or they can be portable and set up at any location.  You may have seen the fixed units if your state requires rolling smog tests where the technician will drive your car at speeds of 15 and 25 mph to test emissions. 

The above is an example of the portable type, which many people use at enthusiast gatherings.  The one below is a fixed unit such as what shops use.

Now you might be thinking, what is the point or purpose of using a dyno?  Dynos aren't just used for bragging rights and becoming someone's internet hero.  They are very useful for tuning.  Dynos are capable of closely replicating road conditions to allow you to tune your car without the risk of hitting road hazards or receiving speeding tickets (typically 4th gear is used as it is closest to a 1:1 drive ratio).  It also allows the tuner to load the engine at a certain rpm and keep it there, which is easier than trying to maintain an exact speed on the road.  Fuel mapping and ignition timing can be tweaked, and the results will be known instantly as to whether performance was improved or hindered.  While the vehicle is on a dyno, it is much easier to keep an eye on important parameters such as oil pressure, water temperature, air/fuel ratios and other bits of information critical to engine tuning.. 

Dyno tuning can help your car perform in more ways that just peak power output.  The goal of many tuners is to create as much "area under the curve" for power.  This means they want to produce as broad of a power band as possible.  A broader power band will make an engine feel easier to drive, and it will not be as much of a chore to keep the engine within its maximum efficiency range versus a car with a narrow power band.  For individuals concentrating solely on peak power numbers, their curves look more like a giant exponential curve compared to the more gently sloping curve of a vehicle with a broader power band.  Street based power maps will have more low end torque, and race based maps will have the curve shifted towards the top. 

Power output isn't the only thing a dyno can be used for.  Some people whose main goal is gas mileage can benefit from dyno tuning.  The tuner can adjust the fuel and ignition maps to generate the maximum amount of fuel economy for a vehicle at the expense of power output. 

Regardless of your tuning goal, when on a dyno, it is imperative to have sufficient air flow to the car's engine.  Since the car is not physically moving, a large fan should be placed in front of the radiator to aid cooling.  Otherwise, overheating and blown engines may result.  Many shops use industrial fans and keep the hood of the engine open to reduce temperatures.  A wideband oxygen sensor is equally important to keep track of the air-fuel ratio of the engine.  If the ratio becomes too lean (not enough fuel), the motor can blow, and likewise if the ratio is too rich (excess fuel), power output is sacrificed. 

As another cautionary note, tuning an all wheel drive vehicle requires that the dyno's rollers or hub mounts be synched and locked, or damage to the car's drivetrain may result.  Some car manufacturers even limit the speed their car can run if any difference in wheel speeds is detected. 

Now you know the basics of dynos and their purpose.  Perhaps this has piqued your interest to see how your vehicle is performing.  If you want to have tuning done to your car, just remember to do your research first and take it to a reputable shop. Be sure to ask plenty of questions before you hand over the keys.  A good shop will be able to recommend what tuning software to use, and will happily go over any details with you.  It is also good to ask some of the local enthusiasts who they recommend in your area.  Happy motoring and keep on driving!

The above is an AWD vehicle being tuned on a dynapack with all 4 hubs mounted.

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