Regular readers will recall that our red, SOHC ’97 ’Stang has evolved through a series of configurations, all in the name of increased output, though not always entirely successful. Basic bolt-ons added a few horsepower here and there, but barely enough to elevate rear-wheel output from its stock 183hp reading to just beyond the 200hp barrier. An Allen Engineering supercharger package, complete with Eaton huffer and a liquid-to-air charge-air cooler, paid big dividends, kicking the 4.6L square in the tush with just shy of 100 extra hp. That success encouraged us to re-cover old ground by installing Ford Racing Parts’ cylinder head and intake manifold package, along with its shorty headers. In naturally aspirated tune, and using the dedicated ECU that had been absent during the first go-round, the Ford Racing upgrades produced 250 rear-wheel horsepower, which we deemed a respectable outcome—particularly when you consider that the factory cams were retained, as well as full emissions compliance.
Enjoying a renewed faith in Ford single-cam “mod-motor” performance, we opted to reinstall the supercharger and associated hardware while retaining the FRP cylinder heads and headers. Best of both worlds, right? Almost—using the ECU included with the FRP top end kit, the Mustang generated 314 hp on Joe Jill’s Superior Automotive dyno, a new high for this project. Unfortunately, detonation kicked in right as the power was peaking, obligating us to back off the throttle and abandon further attempts. This must have been what the FRP instructions were referring to with the warning: “Using forced induction with this programming can result in severe engine damage!” We managed to avoid the damage part, but had to make a change. Swapping ECUs for the stocker resulted in more of the same power-robbing behavior witnessed during prior efforts with factory programming.
We were really into uncharted waters now since we had mixed and matched components, creating a combination that the manufacturers hadn’t taken into consideration. Was this a deserved rap on the knuckles for daring to color outside the lines? Perhaps, if you think hot rodding is about sacrificing. We don’t—we knew these pieces could somehow work in harmony to boost the 4.6L’s bottom line deeper into the black.
We’d use more factory parts; this time a fuel system upgrade kit marketed by FRP to complement its own supercharger kit, one that uses a similar blower though without a charge-air cooler. Included is a set of 30-lb/hr fuel injectors, a high-flow fuel pump, and yet another ECU.
In order to accommodate more intake air, an engine must provide more fuel. This is the cornerstone of internal combustion. The irony is, the classic struggle of the hot rodder typically involves trying to stuff more air into the combustion chambers—the fuel half of the equation is usually the easy part. In the old days, you simply increased the jet sizes in the carburetor (or added a larger carb) to keep the air/fuel ratio in proper proportion.
With EFI, the approach is somewhat different. On the surface, it would seem that an injector swap alone would do the trick, and in fact, many late-model tuners do just that after enhancing the engine’s breathing potential. However, without making adjustments to the engine management calibrations, an injector change is just a means of “fooling” the computer into providing the required increase in fuel delivery.
The logic goes like this: The ECU controls the firing of the injectors based on pre-programmed information combined with input from various engine sensors. The manufacturer bases this programming on the size of the intended injector, so when larger injectors are substituted, the firing times remain similar. While the oxygen sensor can inform the ECU of a richer mixture, this input is not specific enough to cause the injector firing time adjustments required to maintain proper air/fuel ratio. This is particularly true at wide-open throttle, when the ECU goes into “open loop” mode and ignores input from the O2 sensor.
Similarly, modifying fuel pressure, as with an aftermarket adjustable fuel pressure regulator, is another means of altering the rate of fuel delivery without notifying the electronic engine management. This sort of manipulation is more minute, and can actually be used to fine-tune the engine, but it shouldn’t be considered an option when dealing with broad increases in airflow, as with the addition of forced induction.
So what if we approach the problem from the other end—altering the ECU’s programming to provide the desired enrichment? If the reprogramming is handled appropriately, this is a far more accurate means of dialing in the fuel curve. However, even this approach can create conflicts in the face of significant airflow enhancements. The injectors have operating parameters, generally referred to in terms of the injector’s dynamic range. This is the scope of its ability to deliver fuel, from the shortest pulse width to the longest. A stock injector called upon to feed the increase in airflow that accompanies forced induction may be held open almost constantly at WOT under load, placing it beyond its proper operating range. Conversely, a bigger injector may not be able to pulse briefly enough at idle to prevent an over-rich mixture.
The answer is a combination of elements, like the FRP kit. Larger injectors are coupled with specific programming to yield the proper fuel curve to match our supercharged induction system. The only questionable factor remaining was the issue of the kit’s intent—this package was designed to feed the FRP supercharger kit, which provided 6-psi boost instead of the 8-psi our Allen system generated, though ours benefited from the charge-air cooler. We tossed it in and held our breath.
Back on the street, the engine felt demonstratively softer, like it was running fat and was being robbed of timing. Driveability suffered as well. The smoothness had deteriorated, and it felt like several different entities failing to communicate. On the Superior dyno, the 4.6 showed that the factory program took out too much ignition timing. It had 15 degrees total at idle, 30 degrees at throttle tip-in, and a measly 6.5 degrees at WOT. Eventually, the timing wormed its way up to 15 degrees total. Output declined radically to 262.9 hp at 4,900 rpm and 328 lb-ft of torque at 3,500 rpm. At this point we knew that beyond-the-box calibration was the only option.
Steve Cole at The Turbo Shop did his usual thorough job of reconfiguring the ECU to the popular parameters, adding and subtracting spark and fuel from idle through midrange to WOT; he also moved the rev limiter up to 6,000 rpm. Though he accomplished a great deal more than what’s represented in these few lines, he said finally, “It didn’t seem to matter what I did, the power never came around like I thought it would.” We reminded him that he does most of his tuning with the LS1 engine, which is 70 ci larger than the modular Ford. We thought he’d made great progress. Now the red car gets sideways at will in Low gear, and the tires give a healthy squeal in Second; it wouldn’t have done that before if you brought a virgin to a blood sacrifice. Despite Cole’s concern about the power he couldn’t find, he did a masterful job on the Mustang’s driveability. It has smoothness and lightness to its operation, like all the players are on the same team now, like it was done at the factory. On another plane, the smog-check revealed some very interesting numbers: At 25 mph, the 4.6L recorded the following: HC (PPM) 33 max, 10 actual; CO (%) 0.44 max, 0.00 actual; NOX (PPM) 838 max, 38 actual.
What would our enigmatic Mustang’s report card look like now? Back at Jill's, we saw only marginal improvement, scoring 264hp at 5,100 rpm and 338 lb-ft of torque at 3,100 rpm. Though Cole had made the driveability much better, 30 degrees of initial timing, at about 4,000 rpm, began to drop all the way back to 8 degrees total at WOT. We'd like to see something like 22 degrees total (we're realizing 8psi positive manifold pressure), to get the hp up over the 300 rear-wheel mark. Cole will be working hard to make that happen.
