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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.