Join Date: Jul 2002
Location: Somewhere in NJ
"The stock driveshaft can't **reliably** handle the higher RPM's that going faster would create, it would start to balloon".
Yes and no...
There are a few reasons why Ford set the speed limiter at 105 mph on the 4.6L
T-Birds and Cougars. The first reason is...215/70-15 stock Firestone tires are not rated for high speeds. Second reason is, driveline critical speed. Where the driveshaft starts to bend and can possibly take out the rear bushing in the 4R70W automatic. The driveshaft won't balloon, you're thinking of the torque converter. The stock driveshaft is steel and it's crimped to the proper length, not great for sustained high speeds. Even notice what is under the driveshaft on the MN12 cars? Yes, the gas tank. I doubt the rear loop (weak) would save your butt if the driveshaft dropped at high speeds. I don't think you'd drop a shaft from a few triple digit blasts though.
The 12" torque converter is rated for 5,400 rpm, then is starts to balloon or grow on its axis of spin. There is a possibility that it can wipe out the trust washer and that would be BAD. Still this really doesn't pertain to the occassional 130 mph blast some wish to participate in.
The bottom line is, to get around the 105 mph limiter, you need a chip. I recommend SCT for those needs. Then you'll need speed rated tires and at least consider an 11.25" torque converter and MMC driveshaft to be safe. Finally, remember 105 is not legal on public roads.
2008 Acura TSX (5AT)
2012 Honda Ridgeline RTL (w/Navi)
Ex toy: 1995 T-Bird LX - ALLEN supercharged, 2000 Mustang GT 4.6L PI engine, lot's of goodies...
12.74 @ 109.45 mph (BEST E.T. BEST MPH)
325 RWHP/380 RWTQ (SAE) on a dynojet
Tuned by Jerry W. from SCT