Dyno Tuning Preparation

You’ve read every forum and visited every on-line store and in the process spent your rent money, the college fund, and your future retirement on bolt-on Subaru goodies. The point of all this madness is to produce a more powerful platform for whatever your personal performance niche might be: drag racing, autocross, track days, or simply bragging rights. However, with few exceptions, your new parts will produce little power and, in the worst of cases, might actually damage the car without proper tuning.

The critical issue with all power-producing parts is that the computer or engine control unit (ECU) overseeing your engine’s life support processes is completely unaware of its new operating conditions. Simply put, the ECU is not calibrated to make proper decisions in this new milieu of bolt-on goodies. In the best case your engine will survive its new environment and might even make a few more horsepower.In the worst of cases, the discord under the bonnet can destroy the internal engine components.

Fortunately, there are software tools available that allow the Subaru ECU to be recalibrated to harmoniously integrate engine upgrades. Well-respected companies such as EcuTek and Cobb Tuning offer software solutions that allow professional tuners to recalibrate the stock ECU. Other solutions include piggy back computers like the Turbo XS UTEC Delta that work with the stock ECU to control engine function. Professional tuners make sure the ECU calibrations integrate these upgraded mechanical components for both power and reliability.

Getting Ready

The parts are on the car, the tuning appointment is set and you’re ready to make your power hungry dreams a reality. This final step in the upgrade process most often involves getting your car tuned on a dynamometer. Think of a dynamometer as a treadmill for your car that allows the tuner to put the engine under a variety of load conditions to simulate driving on the road.

In this highly-controlled environment, a specific set of conditions can be repeated as often as is needed so that the ECU calibration can be done in a safe, controlled and repeatable fashion. Dynamometers are expensive to own and operate. The initial investment for a shop can be well into six-figures. As a result, dyno time and the time with the professional tuner, while a critical last step in producing safe, reliable power, can be a substantial investment.

In order to get the most out of your dyno tune, the mechanical condition of the car needs to be as well sorted as is possible. It’s a poor use of time and money to fix minor mechanical issues while sitting on the dynamometer.

I’ve personally tuned over a thousand Subarus on dynos across the country so I’ve seen nearly every possible combination of mechanical issues. For the rest of this brief article I’d like to share with you some of my recommendations and those of other Subaru calibrators. These very simple steps will prepare your car for a problem-free dyno session.

Tires – your car’s wheels are going to be spinning on the dyno at speeds well above 100 mph. Proper tire inflation and condition are important. Most dyno facilities won’t allow your car on the dyno with worn tires or tires in poor condition.

Engine Oil – Is the engine oil full and recently changed? The engine will be under a variety of low and high loads. Proper engine lubrication is absolutely critical. It is a regular occurrence for engines to suffer damage due to low engine oil while on the dyno.

According to Steve Talbot, owner of Pacific Import Auto in Tacoma, Wash., “you’d be surprised how many people don’t check their oil before running on the dyno. Low engine-oil levels will destroy or reduce the life of any engine… particularly under high load conditions on the dyno.”

Coolant – The coolant system is going to get severely taxed. Even the best fans can’t replicate the cooling effects of high speeds on the roads. Make sure your coolant levels are topped off. If the coolant is old, have it replaced.

Boost control system operation

Perhaps the single most common mechanical problem encountered on the dyno is lack of proper boost control. The kind of different problems encountered is as varied as are the different mechanical and electronic strategies for boost control. For a thorough explanation of basic boost control see Subiesport issue tech article “Boost Control Basics” or see the same article in PDF format on the author’s website. www.surgelinetuning.com/techtips/boostcontrolbasics.

Or see the technical document from Cobb Tuning outlining the function of the stock boost control system. http://www.cobbtuning.com/info/?ID=3482

Internal wastegate boost control tips:

Wastegate arm pre-tension – Most new turbochargers with internal wastegates do not arrive from the factory with proper wastegate pre-tension. With this type of boost control system the wastegate actuator arm must be under load at rest in order to remain closed under boost. I have found that a pre-load of ½ the diameter of the actuator arm pin is usually a good point to allow proper boost control. Too little preload and boost threshold occurs high in the RPM range and full boost is never realized.

Boost restrictor pill – The “pill” is a mechanical restrictor that limits the amount of compressed air that may enter the wastegate actuator. This restrictor must be in the vacuum line that connects the boost source (usually the turbo compressor outlet) to the boost control system. Without the proper sized restrictor pill, boost control can be impossible to properly tune. Too small a pill will result in higher-than-desired boost that is hard to keep from over-boosting. Too large a pill – less restriction – can allow so much air to enter the boost control system that the solenoid cannot effectively redirect this air away from the wastegate actuator. As a result, boost levels are lower than desired.

External wastegate boost control tips – Connect the boost control lines to the correct ports on the wastegate. There are two ports on an external wastegate: the upper and lower ports. The lower port uses boost to work against the wastegate spring to open it once the desired boost level is reached. The upper port works WITH the spring to hold the wastegate closed. The boost solenoid directs compressed air away from the bottom port toward the top port when boost greater than spring-pressure is desired.

If these ports are hooked up backwards, boost will spiral out of control. Unfortunately, I have observed more than one engine destroyed when a simple mistake – reversing these boost control lines – pushed boost to greater than 40psi less than a full second after boost threshold. This simple mistake is by far the most effective and efficient way to destroy your new engine. Check this twice. Ask a friend to double check it. Ask your tuner to check this if you are not certain.

Electronic boost control tips – While it’s likely your tuner has used nearly every type of boost control system at least a few times, I can speak from experience when I say it’s nice to have the manual available just in case. Bring the boost controller manual with you or double check that your tuner can use your boost controller in his or her sleep. This will save valuable minutes on the dyno struggling with the latest JDM multicolored, multifunction, boost control widget.

Boost leaks – Perhaps the second most frequent mechanical issue encountered when dyno tuning are boost leaks. Some of the most common bolt-on upgrades involve removal and reinstallation or wholesale replacement of intercoolers, intake manifolds, or any number of vacuum hoses. If these parts do not seal properly when reassembled, are not properly tightened, or are simply forgotten, the result is a loss of air from the engine under boost or ingestion of unmetered air under vacuum.

The result is a car that is impossible to tune due to a total lack of fuel and ignition control. The best way to confirm the integrity of your intercooler and manifold is to pressurize the system while the engine is not running using an air compressor. Cobb Tuning has an excellent document outlining how this is done. This article can be accessed via the web at: http://www.cobbtuning.com/info/?ID=3481

Clean spark plugs – Change your spark plugs before the tune. Running rich for any period of time can foul your spark plugs. Changing your spark plugs before a tune is a cheap way to ensure optimum power. In some instances your tuner may recommend a specific type of plug, heat range, or electrode gap. Consult your tuner for specific advice.

External EM setup – Does your car use a separate computer or boost controller? Make sure the serial or USB cables that connect these devices are readily available and accessible for your tuner.

Bring all your parts – Does your form of engine management require special cables or power supplies? Make sure to bring them to the dyno session.

Fuel – Making power is all about burning fuel in the pursuit of mechanical energy. The quality of this fuel will make a HUGE impact of the quality of the tune. Make sure to use best grade of fuel with which you will expect to operate the vehicle. If you wish to also have the car calibrated for race fuels you may want to show up to the dyno session with ¼ tank of fuel. Bring race fuel and extra pump fuel with you to the session.

For further information and alternative opinions about how to get your car ready to make power on the dyno you can also see several online documents from prominent tuners.

P&L Enginesports
http://www.pandlenginesports.com/caringforyourvehicle.pdf

Cobb Tuning
http://www.cobbtuning.com

SurgeLine Tuning
www.surgelinetuning.com/predynoprep

Article: Tim Bailey, Technical Editor