This was supposed to be a gratuitous, John Force-style burnout photo, but during the last
If You've been following the modification of our resident '93 Cobra, Project Stolen Goods, you're probably as ready as we are to know that it's finally running, driving, and turning dynamometer rollers.
Last month, we fired up Stolen Goods for the first time in more than a decade, making sure everything was functioning as it should. After a 15-minute break-in period, we changed the oil and filter and poured in a bottle of D.S.S. Racing's oil additive. We did the same thing again after another 30 minutes.The Meziere electric water pump and Flex-a-lite electric fan worked flaw-lessly, and we had plenty of oil pressure, so it was time to get the car on the dyno.
In order to optimize the combination and get horsepower and torque numbers, we took Stolen Goods to HP Performance in Orange Park, Florida, where our Cobra was strapped to the company's Dynojet. Before we let loose with the throttle, however, HP's Tony Gonyon hooked up his datalogging equipment to see what the engine was doing while he was tweaking the A9L ECM with a custom SCT chip. The original X3Z processor had long since been separated from SG, so a standard 5.0, five-speed ECM would work just fine.
Stolen Goods has been a popular project with MM&FF readers. While out on one of our test d
Professional Mass Air Systems did a great job with the mass airflow calibration, which was tuned to match the 38-lb/hr fuel injectors we used. Mass airflow sensor calibration, however, has to be a middle-of-the-road approach to suit the many different combinations out there. Considering that, and the fact that manual fuel pressure and timing adjustments are one dimensional in their function and only a small part of the tuning equation, we needed to optimize our Boss 347 bullet using an aftermarket piggyback-style computer chip.
We began by setting the base fuel pressure at 40 psi with the vacuum line off and the base timing at 12 degrees. Being able to datalog what's going on in the engine is extremely helpful when you're trying to nail down the proper tune-up, and we realized there were several changes that needed to be made to the program. Because of the larger injectors, the cranking fuel and air tables needed to be altered to allow more air and less fuel for an easier startup. Knowing that we had moved the O2 sensors way downstream, Gonyon delayed the O2 read time. With shorty headers, the O2 sensors heat up quickly, and then they start reading the exhaust. With the O2s placed further away from the exhaust ports in a long-tube configuration such as ours, they need more time to heat up so they can accurately read the exhaust information.
At the start of the project, we planned to use a 3.27 or 3.55 rear gear ratio and opted to
Other changes to the idle and drive air tables which control the IAC solenoid were made, along with a slight reduction in cruise timing to reduce a bit of light throttle bucking that we noticed. Lastly, Gonyon altered the fuel and spark tables to create his own timing ramp and fuel compensation, and he also raised the factory rev limiter to 6,400.
With the tuning finished, the Boss 347 was cranked up, and a full pull was made in Fourth gear. The numbers came up at 342 rwhp and 368 lb-ft of torque. Given the humid temperatures and relative lack of break-in miles, we expect to see a bit more power down the road and during cooler weather. All in all, we got exactly what we wanted-a very torquey motor that, depending on what estimate you use to calculate the drivetrain loss, makes right at about 400 hp at the crank. More importantly, the car is a blast to drive.
A few tuning sessions out on the road followed and all was deemed well except for the rearend whine that we noticed. After disassembling the rear, we found that the pinion bearing had failed, which caused the backlash to be off. Our plan was to get the car on the alignment rack and then get a few street miles around town before returning to HP for a new gearset.
A few days later, we pulled out of the dealership where our friend George Xenos had just performed the alignment. After mildly easing through Second and Third, we suddenly heard a loud tapping from underneath and in front of the car. A roadside audible assessment pointed to a pushrod tapping the valve cover, and that was later confirmed once we had the intake and valve cover off. The reason it was hitting was because the rocker-arm stud had snapped right above the nut. Our contact at Summit Racing had a replace-ment stud shipped in short order.