Hungry for a fresh perspective, you flip open the newest copy of Import Tuner to find an article on 'ECU reflashing'-an engine management strategy that promises to control nearly every function of most late-model OBD 2 engine management through the car's existing hardware and components-allowing tuners to manage engines in nearly any state of tune while maintaining stock-like reliability and appearance...and costing pennies on the dollar! Intrigued, you decide to read on...
The Solution
"The first thing to understand," cautions Tadashi Nagata, powering down a customer's '05 Infiniti G35 after pulling through some runs to establish its baseline, "is why newer cars often lose or make less power with bolt-ons." As supervisor and lead tuner for Technosquare Inc.'s U.S. enterprise, Tadashi has been tuning cars in all states of build for years, and has learned all the tricks along the way. The car at hand has been modified from stock with the addition of some top-dollar bolt-ons: a cold-air intake, headers, a Y-pipe, high-flow cats, an after-cat exhaust, and an intake manifold plenum spacer, to name a few. "Some parts will make power on their own," he explains, motioning to the plenum space rand high-flow cats, "in areas of the car that weren't maximized from the factory. But other parts will lose power; like many aftermarket intakes."
As the conversation progresses, Tadashi-san points out the first apparent drawback to modifying newer cars; they have more sensors. Today's late-model OBD 2 ECUs are able to control more aspects of engine function than ever before. In the case of the G35's VQ35DE Rev-Up engine that Tadashi is tuning, intake airflow, air temperature, manifold pressure, exhaust gas temperature (x2), throttle pedal inflection, and load are all monitored, while throttle position, ignition timing, cam timing, and fuel injection can all be adjusted to compensate at the ECU's will. Because of this, if the readings of certain sensors fall outside predetermined parameters, the whole system can lose balance.
In MAFS cars like the G35, changing the OE intake for a less-restrictive aftermarket unit often means swapping the MAFS into larger diameter piping, "...which slows the speed of the incoming air," explains Tadashi-san, "fooling the ECU into thinking there's less of it." In return, less fuel is injected, Air/Fuel ratios (AFR) leaned out, and exhaust gas temperatures (EGT) rise. In some instances, the leaner AFR might actually make some additional power, but in others the increased EGT readings of newer cars' wideband O2 sensors will prompt a compensatory change in ignition or cam timing, limiting power gains.
Similarly, since a fairly large amount of valve overlap is used at the low rpm factory tune to compensate for a car's restrictive stock exhaust system, once the restrictions are lost with the addition of freer-flowing aftermarket system, exhaust gases can be scavenged from cylinders more quickly, meaning more clean air can enter the cylinders at low rpm, leaning out AFRs again. And since low-rpm performance benefits from the longer combustion times of richer AFRs, backpressure actually helps torque production in the lower rpm. In many instances, engines' cam profiles and variable timing features are optimized to make the best all-around power in conjunction with OE-spec exhaust components-upgrading the flow capacities of these systems can put a hurtin' on power.
...
>>next page