Standing idly beside your hometown performance shop's Dynojet for the second time in a week, you eagerly await testing to commence on your daily driven '06 Nissan 350Z. You're a newcomer to building up late-model performance imports, but not to the tuning scene altogether; you and the shop's crew strapped more than a few past project cars to these rollers back in the day-but you hadn't picked up a wrench in years until a few weeks ago, when you decided to modify the car with a few modest bolt-ons. Until that point, you had driven it factory fresh since buying it new, fearing that adding the first part would trigger a relapse; you know where that path leads all too well...and you're not letting the only new car you've ever owned end up a track machine or parts donor.
Your first step was to replace the stock exhaust with a larger diameter, straight-through aftermarket alternative. The new exhaust's structural improvements were apparent at first glance, and the trusty butt dyno registered a positive gain in power after the installation. Following suit, you yanked the OE headers and large, dense catalysts for higher flow replacements that seemed to bring even more ponies to the stable; the exhaust note grew more aggressive, and your Z seemed to race toward redline far easier than before. Finally, you tackled the last remaining restriction to engine aspiration, and replaced your factory airbox, MAFS housing and intake plumbing with the best aftermarket cold-air induction system on the market. Basic bolt-on mods complete, your Z sounded downright mean cracked wide-open on the highway-it was time to find just how much additional power the mods were worth.
Fast-forward to the present. "I have to warn you," your long time friend-turned-tuner cautions, as he lashed the Z to the shop's in-ground Dynojet, "These newer cars don't make as much with bolt-ons as the older cars did." But you dismiss his words. Baselining at 225 whp before any modification began, your Z belted out almost twice what your B18 did back in the day, and the same mods performed to the Z would've brought a solid 15-20 whp improvement to the 'Teg's front wheels. And judging by the car's on-street performance driving to the shop, you confidently expect at least 30 additional horses. The beast fires up, throttles to redline through a Fourth gear pull, and after a quick survey of the number of shop staff standing around with their fingers in their ears, you feel reassured-30 horses, definitely ...Maybe even 35...
But as the results come back, you're shocked. After the addition of three-time-honored bolt-on modifications-an investment of over $2K-you're told the Z's VQ35 received a bump in power to the tune of 1 whp. 1 whp?! What the f---?!
Now you're confused and a little pissed. The car has definite potential, but you can't seem to find it. You reason that hacking in an air/fuel controller might even things out a bit, but thinking back to the days you battled with piggybacks on your swapped EG induces a panic sweat; you'd rather stock the car than have to deal with check engine lights and spotty reliability. Converting to a standalone EMS is an attractive option-when the day comes that you decide to make your Z a dedicated race machine. And then there's ROM tuning. When you handed over the keys to your last Honda project years ago, Crome was just starting to catch on and the benefits of chip burning were hard to beat for the OBD 1 cars. But you're not dealing with a 13-year-old Integra anymore; your 350 is a brand-new car. Replacing factory chips with custom-burned ones? You might as well write the car's manufacturer directly, and request that its factory warranty be revoked.
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 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.
Factor in knock and engine roughness sensors, and variable boost control present in some newer cars, and the house of cards that is a balanced engine management system grows in size and complexity. But today's increasingly inclusive OBD 2 engine management systems offer a huge benefit in their complexity, especially when coupled with flash-based programming-the ability for tuners to manipulate every parameter of their functioning instantly, and in real-time, to custom-tailor ECUs to govern virtually any engine modification at hand. Information contained in older ECUs was mostly ROM-based, or read only memory; microchips were constructed containing pertinent data and could not be modified. If ECU data needed to be changed, the existing chip(s) containing the data had to be physically extracted and replaced with a custom-fabricated or "burned" chip containing new information-the tedious and semi-permanent process of ROM tuning. "But today's ECUs are mostly flash-based," explains Tadashi, "and tuning them shouldn't be confused with ROM tuning." Changing information contained in flash-based ECUs can be controlled entirely with software, usually through a vehicle's OBD 2 diagnostic port. ...A process called reflashing.
With just a few key strokes on the laptop linked to his customer's G35, Tadashi-san is able to recalibrate MAFS voltage to compensate for the change in incoming air mass, correcting AFRs; adjust valve variability via cam timing throughout the rev range, maximizing overlap at specific stages of engine speed; and adjust ignition timing, throttle position, AFR and fuel cut-off along side it all-to fine tune the whole mix, maximizing the potential of the car's bolt-on power enhancers. In about as much time-and with about as much effort-as it takes to upload songs onto an iPod, Tadashi has tuned the G35's stock ECU to produce better than an additional 10 hp and 15 lb-ft of torque across the entire powerband, with plenty more room to grow, should the owner ask him to get "gutsy". And with a little more work, the ECU could be reflashed to govern forced induction or nitrous injection systems, a full naturally aspirated build, or whatever other crazy power scheme his customer might come up with down the road. ...Or reflash the ECU back to stock, should the car need to be brought in to a dealership for warranty work. "Only once the OEM sensors have passed their capacities," explains Tadashi, citing the MAFS as one such instance, "should the owner consider another option to reflashing." But at that time, we suspect the all-out race machine you feared your daily driver would ultimately become would be ready for that stand-alone EMS.