This article was first published in 2002.
For the ultimate engine development you can't go past tuning on an engine dyno. The engine dyn is often the best place to fiddle with air/fuel ratios, ignition timing, boost and other stuff such as camshaft timing - it's no surprise, therefore, manufacturers and race teams invest so much time running their engines on them.
For the average Joe, however, what does it entail to put your heavily breathed-on motor on an engine dyno? We learned a lot by looking over the shoulder of Bill Hanson, from Adelaide's Bill Hanson Engine Developments...
The biggest headache associated with an engine dyno tune is that the engine and its management system need to be removed from the car. So it's not for everyone, or every car. This isn't such a problem, however, when an engine has been freshly built and, say, a new management system hasn't yet been wired into the car.
A long-standing dyno shop will usually carry a variety of different bell housings to mount various engines to the dyno head. The 'usual' engines such as small block Chevs, Holden V8s and sixes will invariably have an appropriate bell housing already made up. In the case of the hot little 3-cylinder Daihatsu engine seen here, however, a custom bell housing needed to be fabricated - this was made using an old automatic Daihatsu bell housing as a base.
Once the engine is mounted to the dyno, it's time to hook up the water cooling system, fuel system, throttle, 12-volt power and wiring loom.
A supply of cooling water is provided by the tall black tank seen alongside the engine. The thermal mass of the water inside is huge, enabling the dyno operator to run the engine at the water temperature of their choice. The fuelling system found in Bill's engine dyno facility is based on a high-flow Bosch Motorsport pump. If need be, however, the fuel pump to be used in the car can be employed.
The engine's electrical sensors (used by the engine management system) are connected to a computer inside the control room via extension leads. Seen in this photo are the sensors for throttle position, intake air temperature, fuel pressure and the three separate fittings for obtaining manifold pressure. The engine's alternator remains connected in order to charge the dyno room 12V battery.
Bill's dyno is produced by American company SuperFlow and is known as a 'water brake' dyno. The head of the water brake dyno contains a rotor that spins in a large watertight housing. As it spins, the rotor pushes the water outward into water cups mounted on the inside of the casing. The engine's power is dissipated into the water, which has the additional benefit of being used as a cooling medium for the dyno head. The water brake dyno is quite good at holding a constant engine load.
Bill says his SuperFlow dyno (model SF901) is rated at 1100 horsepower and can hold a massive 1000 lb/ft of torque. That's plenty big enough for most street and race engines!
There are two separate control systems used simultaneously during tuning - the control for the dyno and the interface for the engine management system.
The first step is to adjust the dyno to the desired settings. This involves entering barometric pressure, vapour pressure, the specific gravity of the fuel (determined using a float in the fuel tank) and the desired rpm test range.
Next comes the selection of the ramp rate. Bill's SuperFlow machine can accelerate the engine from 25 rpm per second to as fast as 2000 rpm per second. Note that the faster the ramp rate, the lower the measured power figure - that's because a portion of the engine's power output is being used to rapidly accelerate the rotational speed of the crankshaft. Where desired, the SuperFlow can also do 'step' tests at 250 or 500 rpm intervals, though this is not often done with turbo engines due to heat issues. Step tests provide the highest possible measured power output for a given rpm, because no power is being used to accelerate the rotational speed of the crankshaft (that is, the engine speed is constant when the power is being measured).
The start and upper test rpm are set into the control panel. Then the operator applies full throttle and the dyno automatically locks the engine down to the start rpm (in the Daihatsu's case, the run commenced at 4000 rpm). Once the dyno has stabilised full load rpm, the operator pushes the Auto Test button to ramp the engine up at the preset rate. (The advantage of the Auto Test facility is its ramp rate consistency.) Once the engine reaches its upper test rpm (7000 rpm in this case), the dyno whacks on a heap of load (to help prevent over-revving) and the operator throttles off.
During a run, Bill's dyno samples data at every 250 rpm (though newer models are said to have better resolution again). Bill's dyno facility allows measurement of fuel flow and fuel pressure, water temperature, oil pressure, oil temperature and engine rpm. In addition, he watches air/fuel ratios with a highly accurate MoTeC 4-wire oxygen sensor, and an ANSON Systems knock sensor detects detonation.
This is an example of the data sampling software of the SuperFlow SF901. You can see how the 250 rpm sampling rate provides a wealth of information - retard the ignition timing a smidgin, for example, and you can see exactly what effect it has between the measured rpm range. The 1-litre 3-cylinder turbo Daihatsu engine pumped out 160 lb/ft at 4750 rpm and a 152hp peak at 6000 rpm (more power came after some camshaft timing adjustment).
The initial set-up of the engine management system - a MoTeC M4 in this case - includes telling the computer what sort of fuel, ignition and sensor arrangement it's running with. The main menu (as seen here) includes headings such as injector scaling, number of coils and more.
The 'base mapping' of fuel and ignition comes largely through experience - knowing where an engine might need ignition advance, or where it might be safest running rich comes from prior knowledge and experimentation. Bill enters the initial batch of timing values very conservatively and first focuses on the amount of fuel flowing through the engine. Bill says he aims for air/fuel ratios of 13.2:1 in a naturally aspirated engine or 12.3:1 in a forced induction engine.
Ignition timing can then be set to suit two different fuel brews - as was done here. The first runs were done running 98-octane pump fuel, while a 'jungle juice' was used to see if more timing would release even more power. Both sets of ignition tables can be logged for future reference.
Some high-end programmable management systems (such as MoTeC and Autronic) feature a self-mapping function for fuelling. Using the appropriate air/fuel ratio probe, these systems can automatically fill-in the data for the whole of the fuel map. All that's needed is one starting point fuel figure and then it's able to do the complete rest of the map. Simply enter the air/fuel ratio required at the various combinations of load and revs, and the system then works out the correct injector pulse widths to achieve those figures.
Not surprisingly, self mapping functions greatly reduce the time required to tune a system.
Bill comments that the key to an effective dyno session lies in consistency. The operator should wait until exactly the same intake air and water temperatures are seen before commencing each run. A fan can also be used to maintain stable temperatures across an air-to-air intercooler.
Interestingly, to ensure maximum consistency, the access door to the dyno room should be kept closed for each run. Having the door open for a run may affect airflow through the dyno room and have an affect on power. That's some of the reason why chassis dyno runs must be taken 'with a grain of salt' when comparing one car's figure to another car's figure on different dynos on different days. There are so many variables that will affect the number printed on the dyno sheet.
Costs and Advantages
Engine dynos are the ultimate when it comes to tuning. They offer accurate rpm and load control over the engine, maximum sensitivity to engine changes and - perhaps most importantly - a variety of instrumentation can be used. These include quick-response air/fuel ratio sensors and exhaust gas temperature probes that may positioned at each exhaust port, where required.
In comparison, tuning on a chassis dyno is subject to inaccuracies caused by wheelspin (especially in the case of ultra-high powered vehicles) and there's considerable load placed on the vehicle's cooling and driveline configurations. The cooling issue - without the car moving through the atmosphere, the cooling system is taxed beyond its design intents - can have a greatly negative effect on the validity and effectiveness of the test. Torque on the chassis dyno is also measured in tractive effort - a unit that has limited basis for comparison with factory-published flywheel figures.
Not surprisingly - due to the set-up time, the expense and maintenance of specialised equipment and tuning time and experience - a well-developed set of maps for your new mountain of muscle costs good money. Bill has a standard charge of AUD$770 per day, plus the cost of oil and fuel.
That's a fair slice of money, but when you look at the 'big picture' it really doesn't make sense to skimp on tuning quality when you've invested so much in the rest of the engine. The last thing you want is an under-performing hardware combo - or worse, a set of melted pistons caused by lean-out.
Bill Hanson Engine Developments
+61 8 8362 8545