Muscle Mustangs & Fast FordsHow To Engine
Project Silver Stealth Performance Mustang 4R70W
Performance Automatic Rebuilds Our Tired 4R70W In Project Silver Stealth Stang.
We decided to save money by using our existing core rather than spending the extra cash for another one. We shipped our box to Performance Automatic (PA) for the rebuild. When the company received the transmission, the team tagged the unit in order to keep track of it. Our 4R70W was cracked open and inspected before any modifications were made.
Tom Cyr handled the disassembly and rebuild of our transmission. Cyr reported to us on the condition of our high-mileage unit: "The Overdrive band showed signs of overheating, while the other bands are worn out. This is typical for high-mileage and abuse." Despite the worn bands and overheated Overdrive band, the trans still shifted and operated, but it wasn't ideal.
Performance Automatic rebuilt our transmission keeping in mind our intended use. We aren't looking to run a heads-up NMRA class or chase a championship with a high-horsepower engine under the hood. The car is a daily driver, and at most, the engine might see a small hit of nitrous. That means we don't need to upgrade the 4R70W to Performance Automatic's top-of-the-line Super Comp option, so we elected to go with its Super Street upgrade.
Cyr added new seals, bushings, Alto Red Eagle clutches, bands, a modified valvebody, and other little parts. Once the transmission was assembled, it was tested on an Axililine dyno. A special computer was hooked to the transmission, mimicking the factory ECU. The transmission was driven on the bench, and the computer put our freshly built 4R70W through a barrage of simulations to test shift rpm, firmness of the shift, and lockup pressures among other things. It's a way for the shop to verify the trans is operating properly before shipping it back to the customer.
Then the fresh 4R70W transmission was shipped back to Radical Racing, where Silver Stealth Stang sat in anticipation. Once the car was in the shop and on the lift, the trans bolted in quickly and easily. By reusing our transmission, we knew there wouldn't be any issues with fitment. The Axle Exchange aluminum driveshaft was bolted back in, as well as the Bassani exhaust system. Miele noticed an immediate improvement during his testdrive. "The transmission shifts really nice now around town. It isn't lazy at all. The tires bark at each shift when I am at WOT too. Before the car would feel really lazy on the shifts. The transmission is noticeably better than stock," Miele said.
While the car was in the shop, we took the time to add some more parts. Downs Ford Motorsport shipped over a set of Ford Racing 30-pound fuel injectors. It wasn't that Silver Stealth Stang was severely lean, but Radovich felt the air/fuel ratio at the top of the chassis dyno pulls wasn't optimal. Miele had added a fuel pump from an '03 Cobra, so we knew it wasn't fuel-pump related.
We don't expect the 30-pound injectors to magically make 50 more horsepower. Instead, they were installed to keep plenty of fuel in the cylinders in all conditions. The larger injectors will also allow us to add nitrous or more induction components without the fear of running out of fuel.
By changing the fuel injectors, the ECU is affected thanks to the MAF sensor system. A MAF sensor measures incoming air and commands the fuel injectors to spray what is required to support that volume of air (and engine load). That said, if the injector size is increased, then the ECU's parameters have to be modified to compensate for the larger-volume injectors.
There are two ways to adapt for large injectors; manually adjust the ECU tables using tuning software from companies like DiabloSport, SCT, and many others. The second option is to change the MAF sensor to a unit that is properly calibrated for the injector size. It basically sends a signal to the computer based on the injector volume.