Now you have to be asking, how did the JPC gang link up the transmission to the factory computer system? In either an auto or manual shifting application, you will need to get a Mach 1 or 4R70W transmission wiring harness (PN XR3Z-7C078-BA). For those going the manual-shifting route, the neutral safety switch plug from your S197 harness goes into the LenTech transmission without any problems. The reverse lights and speed sensor are required to be spliced to the trans sensors since you're combining two different harnesses. LenTech has an instruction manual online that includes a highly detailed wiring schematic. It's so clear and easy that we would rather you reference that diagram directly. There are just a few wires that have to mate up. The lockup and overdrive functions are wired to a button, which we mounted in the cigarette lighter hole and ran like a regular 12-volt power switch.
Kevin MacDonald of DiabloSport handled the tuning, and he informed us that the tune wasn't too different than what one would expect. He said he mostly corrected for the engine's power, 620 rwhp and 578 rwtq. Other than that, the computer simply ignores the transmission, since it thinks there is a manual stick shift box in place. The speed sensors work just fine, as do the reverse lights and overdrive functions. The car starts fine since the neutral safety switch is active.
So what about the driving impression? In a word; fun! That is the easiest way to sum up the experience behind the wheel. For those who have driven a full-manual valvebody automatic ride, it is the same with firm shifts, except you yank the shifter. We love the switch for the overdrive, as you simply run the car up in Third gear and flip the switch as you get to cruising speed. Thanks to the time of year for this article, we were unable to get track performances with the new transmission. Rain and cold weather put a damper on the fun, but Burcham says the car is definitely a nine-second street car.
Converting your S197 to a 4R70W transmission will certainly keep your Mustang on track and out of the transmission repair shop. There comes a time when the 5R55S should be shoved aside for something a little beefier. With winter upon us, now is the perfect time to make the swap to a 4R70W.
Transmission Lingo
Some people might be wondering what is a 4R70W and what is with the goofy name? The transmission name is simple; 4 stands for four-speed, R for rear-wheel drive, 70 is the torque rating (700), and W represents wide-ratio for the gearset. It came in '99-'04 Mustang GT models. Ford also produced the 4R75W, which is the stock '03-'04 Mach 1 transmission and is nearly identical to the 4R70W--with a 750 lb-ft torque rating. The 4R70W trans is a very popular transmission and easy to find, where the 4R75W is a bit more difficult to locate in junkyards and such. Ford also has a 4R100 transmission that comes standard in the Lightning trucks and other models. We have heard of this transmission being used in Mustangs, but the 4R70W is by far the most popular due to the ease of locating a core at a reasonable cost. The 4R70W is also strong enough for just about any combination given the aftermarket's modifications to the internals.