Thread: 2nd prime
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Old 01-06-2012, 10:37 AM
TNC TNC is offline
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Quote:
Originally Posted by 2011lilred View Post
While the 545RFE came from the 45RFE and one could argue the 45RFE is based on the Torqueflight family with additional planetary gears, the gear spacing issue is has nothing to do with it since the 727 uses 2.45:1 in first, 1.45 in second, and 1.00 in third while the 545RFE uses:
  • 1st 3.00:1
  • 2nd 1.67:1
  • 2nd Prime 1.50:1
  • 3rd 1.00:1
  • 4th 0.75:1
  • 5th 0.67:1
(Note the similarity to the 700R4 ratios of 3.06, 1.63, 1.00, 0.70)

If you take 2nd Prime out of the upshift sequence, the gear spacing is just fine. The whole 2nd Prime gear came about simply as a taller passing gear to avoid downshifting all the way down to the 1.67 gear when you stomp on it on the highway. As you would likely be in an overdriven gear at the time, jumping all the way down into the traditional 2nd gear causes rpms to skyrocket - again, note the similarity to the 700R4.

2nd Prime was not originally intended as an upshift gear, it just morphed into one.
Thanks for that info on the trans background and ratios. I realize that this is the drag racing forum segment, and more gear selections usually relate to better performance times/numbers.
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