In checking what works in many enthusiast forums for late model cars, there are often debates whether an air intake helps power as the power gains are often smaller than the uninformed enthusiast can resolve in simple dyno testing. Often an air intake can make a good gain but the ECU's self learning function dials things back and the new found power goes away after a little bit of driving or sometime over the course of a few days or weeks. Some cars are notorious for returning to near stock power levels after driving with mods for some period of time.
You might wonder how this happens. Well a cold air intake improves power three ways, first they are usually less restrictive and improve volumetric efficiency by reducing pumping losses. Second the intake tubing length and diameter are tuned to resonate over a useful part of the engine's operating range to provide a slight degree of resonant supercharging to improve the engine's volumetric efficiency over a relatively narrow range. Finally a cold air intake can often drop an engine's intake air temp to improve intake charge density which increases power.
Well changing an engine's intake system can greatly change the output voltage curve of the MAF. This can trip check engine lights and or cause the engine to operate in cells of the fuel and spark tables under the wrong conditions, the engine can run too much or too little timing and fuel. If the intake is tuned on the dyno simply for power, it can run with slightly more advanced timing and leaner air fuel ratio for a while and register more power. When this happens on a late model engine the engine's closed loop control often detects the issue and corrects fuel and even timing values to its own internally referenced nominal operation state, effectively dialing out a good percentage of the newfound power gain. On some cars this can happen even with some apparently well designed intakes from reputable manufacturers. The better intakes can hold on to their power gains longer and perhaps they can lose less but sometimes they still lose power on some cars.
Recently we got to review an intake using some new technology. AEM has recently started to release their new line of electronically tuned air intakes or ETI intakes for short. The ETI intake is an innovation that should give AEM intakes a power advantage even on some notoriously difficult to improve upon cars. ETI intake uses a mappable converter box to correct the MAF voltage curve to resemble the stock curve no matter what the configuration of the intake. The converter box allows AEM's engineers to design an intake for the best power without worrying about check engine lights and the engines closed loop control.
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