Tuning a performance racing engine is no longer a shamanistic ritual of tricks, spells, potions and tribal knowledge. While secrets do lurk in every corner of motorsports, the empirically-driven management systems of the aftermarket like AEM’s Infinity work with much more transparency and logic. So close your tome of powerplant enchantments in exchange for some enlightenment thinking.

Screen Shot 2016-04-19 at 2.44.14 PM copyEngine management computers, software and interfaces vary in structure, ease of use and schools of thought. Among some of the most advanced methods is volumetric efficiency-based tuning. Volumetric efficiency (VE) tuning works on the principle that a given engine makes concessions and trade-offs to optimize a powerband suited to it’s unique application. An engine that exhibits very high volumetric efficiency in one area of the power curve will likely suffer in another area. Volumetric efficiency is simply the percentage of actual cylinder displacement being moved through the engine, inertial effects and timing play a great role in this determination so VE is highly rpm-driven.Screen Shot 2016-04-19 at 2.44.55 PM copy

Engines are air pumps, and as articulated in the video — the more air one can force through a given cylinder displacement and valve-train assembly, the greater the potential to make power. The efficiency of an engine to move air changes across the rpm band as a result of a multitude of factors — some of these include camshaft profiles, intake and exhaust runner design, and valve-train. “An engine’s volumetric efficiency is directly correlated to its torque output. Simply put, the more efficient the engine is at moving air, the more torque it will produce,” explined Nathan Stewart of AEM. Knowing how to fuel this combination is where VE-tuning comes into play, “A true speed density VE-based fueling control requires significant processing ability as lots of calculations are constantly being performed, however, it is the more scientific and mathematical way to control fueling,” Stewart continued..

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Metering accurate but dynamic fuel delivery along this changing continuum of air flow is where VE-based tuning comes into it’s own. The AEM Infinity system uses a few key pieces of data to plot a predicted VE chart. The user needs to supply the air flow — which is easily calculated with a known displacement and rpm, fuel injector size, and a target air-fuel ratio. With these reference points the VE-based software creates a fuel-delivery plan to complement the efficiencies of airflow across the rpm spectrum.

Screen Shot 2016-04-19 at 2.47.27 PM copy“When you’re tuning a fuel-injection system based on volumetric efficiency, what you’ve essentially done is reverse-engineered or characterized the engine. Once you have a fully-tuned VE table you now have a map or indication of how much air that engine moves at all different conditions — what’s really nice about that is it’s an indication of how much power the engine is making at all points,” explains AEM engineer Hara. “The volumetric efficiency of the engine was set when you bolted that valve cover on, it’s dependent on the hardware of the engine.”

What VE-tuning does for the engine builder or dyno-tech is remove some of the arbitrary guess work — making stabs at target A/F ratios and fuel map. Instead the engine management uses the know engine parameters of displacement, number of cylinders, injectors and projects an appropriate map. “A pulsewidth-based fueling control has a fuel map that simply says deliver X amount of fuel (in milliseconds) at this engine speed and load,” highlighted Stewart.

“Neither the system or the tuner will have any idea what the resulting A/F ratio will be until the fuel has been delivered and the combustion results are sampled by a wideband O2 sensor. This type of fueling control is very simple and easy to run, thus many older systems that had limited processor capabilities used it,” he continued.Screen Shot 2016-04-19 at 2.45.56 PM copyMoving away from the unpredictability of pulsewidth-based tuning, builders are not left guessing how long of an injector burst will net a given A/F ratio. VE-based tuning does that part of the math for you. This allows the focus to be shifted off the stoichiometric side of tuning and onto the more specialized and enjoyable parameters. “Even getting started, you can apply some pretty rough and basic VE-based values into the VE table and get an engine to start and make loaded dyno pulls fairly quickly. Most engines will idle around a VE of 40-50 percent and as we know, and engine will run at or near max volumetric efficiency at its highest load state so a tuner can preemptively set the top of the VE table to 100 percent and be pretty close,” concluded Stewart.

If you are interested in allowing the processing power of AEM’s Infinity engine management system run your fueling, or have any questions on the system give them a call.