5R55 trans in a Mark VIII

[chris2523]

yeah, that's how my mom's similarly weighted LS with a 40 hp disadvantage can keep up with my car from a slow roll, it has an extra gear.

 

[driller]

After further review, the change in gear ratio would require a change in converter stall because of the torque multiplication when unlocked. My data suggests the overall torque multiplication I achieve in 1st gear is about 1.7 which is pretty good considering it would be nearly zero multiplication at the shift point. This suggests over 2.5 torque multiplication at launch. The converter math is really fuzzy at best and is really the wild card in all this.

Which brings another question... in the 5R55 is the torque converter typically locked at WOT in second gear? My calculations presume it is locked in 2nd and above and ignores any post-shift lockup delays.

 

[chris2523]

Which brings another question... in the 5R55 is the torque converter typically locked at WOT in second gear?

my research says not stock, no. but that it can be done with a tune.

TC Lockup and Timing:
Been checking my datalog for TC commands for lockup and looks good. Have talked different companies about when they lock up the trans and what gears. Seems that 2 schools of thought prevail. First some of the trans tuners like to give lockup commands in 2nd, 3rd and 4th gears. Timing is critical for these commands but get more power throught the trans in each gear. The results are lower ET's and lower trans fluid temps, I'm not going to attempt these changes since they can be tricky and lead to damage if you don't get it right. The other school likes to only lockup the trans about halfway through 4th gear, this saving wear and tear on your drivetrain and leaving less possibility for something to go awry during trans shifts. This is where a good tight converter is needed since you will be in hydraulic coupling most of the time. The stock trans program dosn't call for converter lock in 2nd, or 3rd, not until 4th gear after 40mph will you get lockup.

http://www.windycitystangs.com/forums/showthread.php?3029-Project-5R55S-Transmission

 

[driller]

I have another acceleration program that I never could quite get to replicate my actual datalogs but I tried it as well. It too showed the acceleration with the 5R55 better than with the 4R70W. It would drop a quarter mile ET of 12.818 down to 12.663.

 

[chris2523]

.2 or .3 seconds faster in the 1/4 is not bad at all. very cool.