automatic transmission strengths and weaknesses

Do the J-mod (search for that, basically a shift kit) and install a tranny fluid cooler and it'll hold 400+ easily.

Oh, and the transmission in your car is a 4R70W. You can search that for tons of information.

If anything, the 4R70W tranny is know for being one tough SOB. It is one of the strongest tranny's that Ford has put in any of their cars. They'll handle a ton of power even with being negleted. With proper maintenance and mods (tranny cooler) they'll last forever.

In fact the 4R70W has proven to be significantly stronger than the 5R55S autos that are in the 05+ S197 Mustangs.

My stock (except for trans cooler) 4R70W held 240 rwhp / 290 rwtq for 70,000 miles and 400 rwhp and rwtq for an additional 30,000 miles with no problems. They're good transmissions.

FWIIW, the name of the transmission gives some insight into it's ratings.

4R70W.

4=number of forward gears.
R=rear wheel drive
70=itorque rating in 100's of Nm. 700 Nm = 516 ft-lbs
W=wide gear ratio

Note, the transmission has to withstand the torque of the motor plus the torque multiplication that occurs through the torque converter. Hence the reason why some F150's with the 5.4 need a 4R75W even though the motor itself does not make 500 ft-lbs of torque.

Interesting fact. The 5R55S automatic transmission is actually a down grade in the torque holding area. 550 Nm = 405 ft-lbs.

If you want an automatic transmission to last, keep the fluid from over heating.