EFI Tuning - How It Works


Stephen Kim Jul 30, 2012 0 Comment(s)
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Getting Started

After installing the XFI 2.0 system, following these five simple steps are all that is required in order to fire an engine up for the first time. Step one is picking out a baseline tune that is comparable to your application from our library of files. Next, the optional parameters must be set. This includes selecting between bank-to-bank or sequential injector firing, and setting up the ignition strategy and crank reference angle. Afterward, it’s time to dial in the fuel calculation parameters, which involves entering in the engine displacement, injector size, and the fuel energy constant. The final two steps are entering the engine’s firing order, and performing a sensor calibration. As long as you’ve entered the correct baseline tune, the engine is ready to fire up at this point.

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Tuning location

Some tuners prefer dialing in an engine on the dyno, while others prefer doing it on the street or at the track. Where you choose to tune a car depends on which part of the tune you’re trying to optimize. The best way to initially tune the wide-open throttle fuel and spark maps is on the dyno. The controlled environment of a dyno cell is perfect for making small changes and optimizing the cylinder-to-cylinder fuel distribution and timing effects on each cylinder. However, there are also advantages of tuning at the racetrack, as it gives you an opportunity to make changes on shift transitions and the opportunity to optimize the tune for specific track conditions. The track also loads the motor differently than the dyno, so track tuning can offer a more precise calibration for race day. As far as the idle and part-throttle tuning, that is best achieved when you’re actually driving the car down the road.

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Common Screens

Tuning aftermarket EFI systems can seem confusing because there are so many different screens and tables to navigate. Fortunately, familiarizing yourself with the most commonly used tables can simplify the tuning process. In practice, the Base VE table and the base spark table are the two screens that are by far the most frequently used when tuning. These tables are the basis for fuel delivery and ignition timing, so learning to navigate them pays large dividends. There are also multiple tables that are used to set up the cranking fuel, acceleration enrichment fuel, and cold start fuel as well. However, if you choose the proper baseline calibration file, then these tables will need very little attention.

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Setting Max Timing

There’s a fine line between advancing the timing as much as possible for maximum power, and advancing it so much that the motor detonates. To walk this fine line, remember that as you approach the ignition advance for maximum torque you’ll see a point of diminishing returns. If you have a dyno that allows you to hold the engine speed at a steady state, you can easily establish the proper timing value for maximum torque at that engine speed. Some engineering books refer to this timing value as MBT, or maximum brake torque timing. Once you exceed this number, torque values will decrease. If you keep increasing the timing value you will eventually get into detonation. An experienced tuner will recognize the MBT value and stop advancing the timing before you reach the detonation point.

Fuel and Spark vs. Engine Load

Unlike a carbureted motor, EFI systems can monitor engine load as a means of dialing in the fuel and spark. This is a very useful feature, since the amount of fuel and ignition timing an engine requires varies as engine load changes. As a general rule of thumb, you can run maximum timing and relatively lean air/fuel ratios when an engine is operating at the low load areas of the table. This is when you’re just cruising and the engine is under very little load. As far as timing is concerned, when an engine is at very low rpm, such as at idle, you do not need much spark advance. Under these conditions, you will typically have a fairly lean air/fuel ratio that’s not too far from the stoichiometric ideal. Conversely, the air/fuel ratio will be the richest at WOT.


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