What is Dyno Tuning?

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How is dyno tuning accomplished? This discussion will be centered around tuning vehicles with electronic fuel injection (EFI), where the system allows for adjustments to the engine control unit (ECU) through the use of computer software or hand held control modules. The process is very similar for carbureted vehicles with mechanical ignition timing, except fuel and ignition adjustment are made with screwdrivers and wrenches instead of computers.

Dyno tuning begins with an overall inspection of the vehicle's integrity. The car must be mechanically solid, capable of withstanding the rigors of repeated loading by the chassis dynamometer. The most common problem identified is overheating due to inadequate cooling systems. It is virtually impossible to tune a vehicle that overheats.

Getting Connected.... at a minimum, the following information must be measured and analyzed in order for us to tune your engine: Air to fuel ratio, fuel injector duty cycle, mass air sensor output voltage, ignition timing and fuel pressure. Similar to how a doctor uses an EKG to monitor your heart, this equipment enables us to monitor and record your engine's vital statistics during the tuning process and diagnose problems before engine damage results. The importance of these fundamental measurements cannot be overstated. Accordingly, the following outline contains a brief description of each sensor and an explanation of the importance of each measurement:

1.) Air to fuel ratio - This property is derived from measuring the output of a wide band oxygen sensor. The sensor measures the amount of oxygen in the combustion products. The associated signal conditioning equipment is calibrated to translate exhaust gas oxygen concentration into an air to fuel ratio. The equipment is capable of measuring air to fuel ratios from 10.5/1 to 17.9/1. This measurement is invaluable during every stage of the tuning process. Improper air to fuel ratios are often associated with the following problems: poor idle quality, power loss, misfire, stumbling, hesitation, knock, high exhaust temperatures, backfire and poor mileage.

NOTE - This equipment should not be confused with the oxygen sensors commonly found on production emission vehicles. The oxygen sensor used for emission control is narrow band, and is limited to measuring the state of exhaust gases in relation to stoichiometric, which corresponds to an air to fuel ratio of 14.7/1. Connected to the proper control equipment, and used with the appropriate control algorithm, the narrow band oxygen sensor can be used in an EFI system to help maintain air to fuel ratios near 14.7/1. However, for measurement applications, the narrow band oxygen sensor is unable to resolve air to fuel ratio with any meaningful accuracy.

2.) Fuel injector duty cycle - Fuel injector duty cycle has a direct impact on air to fuel ratio. Improperly sized injectors are common for EFI systems. Oversized injectors cause poor idling, bad fuel mileage and sluggish low load throttle response. Undersized injectors go static under high load causing poor fuel vaporization and improper fuel distribution inside the cylinder which results in engine knock and power loss. Moreover, undersized injectors limit fuel delivery causing dangerously lean combustion mixtures under heavy loads.

3.) Mass air sensor output voltage - The mass air sensor is part of the EFI system and is used as the primary means to measure engine load on mass air systems. In combination with the voltage to mass flow rate transfer function, this measurement is essential in determining where adjustments are made on the fuel and spark tables in the ECU. Also, this measurement enables us to verify the mass air sensor is properly sized. An oversized meter will give poor resolution during idle and low loads which causes idle surge and stumbling during normal driving. Undersized meters reach their measurement limit during heavy loading, and additional air that enters the engine is not compensated with additional fuel. This causes lean combustion mixtures where the engine is most susceptible to damage,...at high loads and high engine speeds.

*NOTE - The term "sizing" used in the above discussion is in reference to the mass air sensor air flow calibration, not the physical dimensions of the meter. Two mass air meters of different physical dimensions, for instance 65mm and 80mm diameter meters, could have the same size air flow calibration, 0 kg-air/hr to 1500 kg-air/hr.

4.) Ignition timing - Measuring ignition timing is essential during engine tuning. Even though the ECU is programmed for a particular ignition advance, the timing must be verified independently. In our test facility, we have witnessed instances where the ECU was programmed for 15 degrees of advance, but the actual engine timing drifted up to 18 degrees at high engine speed. Since performance engines are usually knock limited, identifying the 3 degree offset between programmed timing and actual engine timing was critical in maximizing the life of the 950 HP supercharged engine.

Improperly set ignition timing can cause many unsuspecting problems, such as poor idle quality, power loss, stumbling, hesitation, engine knock, high exhaust temperatures and poor mileage. Over time, improperly set ignition timing will decrease the life of your engine. Naturally aspirated engines with moderate compression ratios are usually fairly forgiving as long as the timing is eventually set properly. Supercharged or nitrous applications are not, and an improperly setup ignition map will destroy your engine very quickly.

5.) Fuel Pressure - Inadequate fuel pressure causes poor fuel vaporization and improper fuel distribution inside the cylinder which results in engine knock and power loss. This measurement is a good indication of the overall health of the fuel system, which is comprised of the fuel pump, fuel delivery line, fuel rail, fuel regulator and fuel return line. Pressure across the injectors must be held constant as pressure in the manifold changes. For supercharged cars, this means fuel pressure must increase pound per pound with increases in manifold pressure. For all engines, the fuel pressure should be vacuum compensated to lower fuel pressure as the manifold draws a vacuum. From our experience, the majority of fuel system problems are caused by inadequate fuel delivery line size, inadequate fuel pump size and poor quality fuel pressure regulators.

For cars with superchargers or nitrous setups, we require additional sensors....

Adjusting the idle and low load settings.... The first adjustment made to the system should be to align the base timing with the ECU. Since the spark ignition system does not have feedback, the distributor must be manually adjusted to bring the ECU into alignment. Some ECUs offer a means of doing this through the software, but either way, it needs to be verified and aligned manually.

The next fundamental adjustment made to the system is base fuel pressure. With vacuum off the fuel regulator, the pressure should read at least 40 psig. Depending on the ECU, some expect the pressure to be near a certain value, such as 42.5 psig. These systems are usually original equipment manufacturer systems or aftermarket mass air systems that utilize an advanced algorithm to calculate fuel requirements based on the assumption that fuel pressure is set a predetermined value. For systems that need higher fuel pressure to extend the range of the injectors, it commonly accepted that increases up to 55 psi are acceptable without the threat of damaging the injector drivers or degrading injector motion performance.

At this point, the acceleration enrichment needs to be adjusted just enough to ensure it is not exceeding rich or lean. Since this setting is usually a percentage of the base fuel map, fine tuning of this adjustment should be suspended until the base fuel map is setup.

For vehicles that are idled or driven at low load for any appreciable length of time must be setup to operate properly at idle (no load) and low load before any wide open throttle (WOT) tuning is accomplished. The reason for this is an engine cannot operate properly at WOT if it is forced to recover from or stumble through improperly configured idle and low load settings. Fouled plugs, hesitation, stumbling, sluggishness and backfire are all clear evidence that the following must be adjusted:

1.) Throttle position sensor - This sensor is effectively a potentiometer that supplies a variable voltage output relative to the position of the throttle plates. The use of this output from this sensor varies from one ECU to another, but generally speaking, most ECUs utilize this sensor to determine when the engine is idling and how much fuel to add during transient load conditions. On racing engines with little or no vacuum signal, this sensor is used in the Alpha-N mode, where throttle position is used as a measure of engine load instead of manifold vacuum. We have also seen this sensor used in a control algorithm to stabilize idle lope from camshaft overlap. Also, features such as idle spark control and closed loop fuel control use this sensor as indication to initiate or suspend operations.

The throttle position sensor must be manually adjusted or zeroed through the ECU when the throttle plates are adjusted. Failure to do so will prevent the ECU from knowing when the car is at idle, and therefore cause poor idle and low load operation.

2.) Throttle plate position - In combination with the idle air controller, the throttle plate position at idle has a direct impact on idle quality. If too much air passes the throttle plates, the engine will idle above the target idle engine speed. If too little air passes the throttle plates, the engine will pass excess air through the idle air controller to raise engine speed, and degrade the function of the idle air controller when the throttle plates are snapped shut from an open throttle position.

3.) Idle air controller - The function of this device is to bypass air around the throttle plates to maintain a proper idle. For speed density cars, it is also used to prevent the engine from stalling when the throttle plates are snapped shut from an open throttle position. Another use for this controller is load compensation when the air conditioner is turned on or the transmission is put into drive. Many ECUs have tables that allow adjustment and fine tuning of these settings.

4.) Idle and low load fuel - This is the amount of fuel delivered to the engine during idle conditions. Monitored via the real time viewing of the air to fuel ratio measurement, the amount of idle fuel required by the engine is dependent on various factors. Usually camshaft overlap has the most influence, where large amounts of overlap require slightly richer mixtures to dampen idle surge.

5.) Idle and low load ignition timing - This setting has a direct impact on idle quality. Idle surge, hesitation and sluggish response can be caused by improperly adjusted idle ignition timing. This setting also influences the response of the engine to rapid changes from idle to partial or full load. Properly adjusted, the idle ignition timing will allow the engine speed to respond quickly to rapid changes in engine load that originate from idle.

6.) Control functions - Depending upon the ECU, there are various idle and low load control features utilized to improve drivability, increase fuel mileage, and reduce exhaust emissions. Every ECU implements the control features differently, and some work better than others. The most common control features are idle spark control, closed loop fuel management and target idle speed.

Even though this information has been presented in a form that may seem like a chronological list of steps,.... do not be fooled. This portion of the setup can be extremely challenging since almost every adjustment affects the operation of the others. Radical combinations have required us to make adjustments for several hours just to establish quality idle and low load conditions. Without the benefit of real time viewing of the measurements, it would be nearly impossible to setup these cars properly in any reasonable amount of time.

Develop fuel and ignition curves for high load and WOT.... This portion of the tuning process begins by programming conservative fuel and ignition curves into the ECU based upon available information regarding the engine design and expected power output. By incrementally increasing the load on the engine, adjustments are made to the WOT curves based upon information gathered from viewing the real time measurements.

Make logged WOT passes on dyno.... This differs from the last step in that information will be gathered during WOT passes on the chassis dynamometer for viewing and analysis after each run. During these runs the computer will log all available measurement information from the data acquisition system, as well as measure and record horsepower and torque. By analyzing this information, adjustments are made to the fuel and ignition curves until horsepower and torque are optimized for all engine speeds.

Adjust medium load fuel and ignition maps.... At this point, the idle, load low and WOT portions of the fuel and ignition maps are optimized. All that remains is to tune the medium load fuel and ignition curves. This is accomplished by using the real time viewing function of our data acquisition system in conjunction with the chassis dynamometer controlled loading feature. This unique feature allows us to program portions of the fuel and ignition maps the engine will access during cruising, while climbing and descending hills, and during light to moderate acceleration.

Adjust acceleration fuel.... Even though these curves probably have been under constant adjustment throughout the entire tuning process, the acceleration fuel curves needs to be adjusted one last time since they have probably been influenced by changes made to the base fuel map. This is accomplished easily and quickly on the chassis dynamometer.

Setup auxiliary tables.... There are many ancillary tables and settings available in the ECU. Some of the more common adjustments are warm up enrichment, cranking fuel, air temp fuel correction and coolant temp fuel correction. Settings such as air temperature correction is fairly standard, whereas warm up enrichment is not, and requires time to develop (you only get one shot at adjusting this setting each day).

Word to the wise!.... This generalized outline is not meant as a guide to help you tune your vehicle. Performance tuning is a highly technical business, and as such, this outline is written for the benefit of the paying customer, so that they may better understand and appreciate the service they receive at Woodbridge Dynotech.

Contact Information

13016 Bristersburg Road, Midland, Virginia 22728

email:  [email protected]

phone:  540-752-1600