Muscle Mustangs & Fast Fords
Project Silver Stealth Performance Mustang 4R70W
Performance Automatic Rebuilds Our Tired 4R70W In Project Silver Stealth Stang.
New Edge Mustangs ('99-'04) are quickly becoming ultra-affordable modern muscle cars. They benefit from a solid engine with 260 factory horsepower and a great foundation from which you can build the Mustang of your dreams.
A clean model can be purchased for under $10,000 and still be a street/strip stormer without breaking the bank. Case in point-Project Silver Stealth Stang, which belongs to our esteemed colleague, Ken Miele of the Yo, Ken! column. We began this budget project about a year ago with the goal of netting 12-second times at the dragstrip and be a daily driver. We skipped adding a supercharger or turbo in order to keep costs controllable, and to simply show you a different route in our search for the promise land.
Our quest for the 12s in naturally aspirated trim brought us to the doorstep of Modular Mustang Racing (MMR). As the name implies, the group specializes strictly in modular powerplants. The team assembled a stroker short-block and topped it off with a set of CNC-ported heads and mild Comp camshafts. MMR shipped the bullet across the country to New Jersey, where Radical Racing swapped on the external parts and installed the new bullet in Silver Stealth Stang. On the strip, Miele wheeled the hot rod to a best of 12.85 at 106 mph. It wasn't bad for a mild-mannered street car that knocks down 20-plus mpg on the highway. The car spun the DynoJet chassis dyno at Radical Racing to 285 rwhp with just a mere 150 miles on the new engine.
Truth be told, Miele felt the car had 12.70s or better in it if the automatic transmission would up-shift at a higher rpm level. His post-test report states the transmission was shifting at only 5,800. It was an easy problem to correct inside the ECU programming, but that wasn't the only thing holding back Silver Stealth Stang. The heavier Cobra brakes and 18-inch wheels hurt our quarter-mile times due to the hefty rotating weight. Despite those challenges, the car did run in the 12s without a power adder, lest we forget that the engine is just a Two-Valve mod motor, not the fancy Four-Valve configuration.
There is more lurking under the hood as we continue to employ only 19-pound fuel injectors. Adding 30-pound units will help the lean conditions at the top of the dyno pulls. The stock intake is most likely a restriction as well. We have a JLT cold-air inlet and a TFS upper plenum box, but the long and twisty stock Two-Valve intake behind those products isn't allowing this engine to rev to 6,500 rpm or more. We might be visiting an intake swap in the future.
All this talk of horsepower and dragstrip abuse leads us to this month's task-fortifying the drivetrain. The rearend was rebuilt in the April '09 issue ("Just Roll With It," page 144). Thanks to Downs Ford Motorsport, the 8.8-inch rear has a new set of guts. Radical Racing installed the parts from Downs, including a Ford Racing Traction-Loc differential, 3.73 gears, and new bearings. A lighter aluminum driveshaft from The Axle Exchange was also installed with the rearend setup. A 10-inch torque converter from Pat's Performance Converters with a higher stall-speed (2,800 rpm) was added to help the car accelerate at the dragstrip. The transmission was the only drivetrain piece that hasn't been modified in this 170,000-plus-mile Mustang, but that was about to change.
The '99 Mustang GT is equipped with a 4R70W transmission, which is the follow-up act to Ford's AOD-E transmission. The 4R70W is a computer-controlled transmission and its shifts are controlled by the ECU. It is not overly complicated, unlike the 5R55S in the '05-and-newer models. Silver Stealth Stang's transmission employs four forward gears, plus one reverse: Fourth gear is Overdrive. It's a fairly standard transmission and plentiful in junkyards.
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.
MAF sensor systems are very effective because it can sense larger volume of air going into the engine (due to modifications) and add the required fuel needed to match the incoming air the engine ingests. The MAF sensor is an important part in keeping our cars driving nicely in all situations.
We chose to go with the new MAF sensor and picked up an Abaco DBX meter, the latest MAF sensor to hit the marketplace. The 87mm DBX MAF sensor is unique as it's the first digital meter that allows airflow readings to be taken from four quadrants due to its unique sensor layout.
The DBX is as versatile as it is cutting-edge. The meter is designed for use as both a draw-through and a blow-through sensor. Another interesting aspect of the DBX is its ability to be tuned by the end user. A program can be downloaded off the Abaco website, which allows the end user to modify the transfer functions and tailor it to a specific combination. Also, the DBX can be used on any '89-to-present Mustang as long as it's equipped with a MAF sensor.
We again dyno-tested Silver Stealth Stang to dial-in the new meter and the larger fuel injectors. From the outset, we didn't expect to better our initial pulls of 285 rwhp with just the fuel change. The weather was also much warmer and more humid than during the baseline pulls with the new engine. But to our surprise, Silver Stealth Stang did produce its highest peak power to date at 291 rwhp. It was the extra fuel in the higher rpm that helped raise the power output.
Miele hasn't hit the track yet with the new trans in place, or the injectors and MAF sensor, but he did report that the car feels a lot stronger on the street. In his estimate, the Silver Stealth Stang's 12.85 best should be lowered once he makes a couple of hits.
The project is rapidly coming to a close, but we have a few more tricks up our sleeve to make Silver Stealth Stang a solid mid-12-second player. Stay tuned.