[DeTomaso] Taller 5th gear for cruise

Mad Dog Antenucci teampantera at yahoo.com
Thu Jun 17 22:54:08 EDT 2010


Great Idea.

Mad Dawg Antenucci 
Team Pantera Racing 
The 1st & still the only vintage race team in open road racing 
www.teampanteraracing.com




________________________________
From: Daniel C Jones <daniel.c.jones2 at gmail.com>
To: Pantera REALBIG forum <detomaso at realbig.com>
Sent: Thu, June 17, 2010 12:41:09 PM
Subject: [DeTomaso] Taller 5th gear for cruise

I've decide to have a taller 5th gear installed in the red Pantera's
transaxle.  The standard 5th gear is 0.705.  The optional 5th gear
ratios are:

  0.655
  0.642
  0.620

The tallest 5th gear with the standard ring and pinion is very similar
to the standard 5th gear with the 3.77:1 ring and pinion:

0.620 * 4.22 = 2.61640
0.705 * 3.77 = 2.65785

I ran some numbers assuming:

335/35/17 tires
4.22:1 final drive ratio
current gear ratios
  1st 2.23
  2nd 1.47
  3rd 1.04
  4th .846
  5th .705, 0.655, 0.642, 0.620

Speed  Ratio  RPM
80 MPH  .705  3050
80 MPH  .655  2834
80 MPH  .642  2777
80 MPH  .620  2682
70 MPH  .620  2347
60 MPH  .620  2011
60 MPH  .642  2089
60 MPH  .655  2125
60 MPH  .846  2745

Typical highway cruise speed is 75 to 80 MPH.  The engine is a 407
Fontana with C302B heads and IR EFI.  Looks like I should be able
pull the 0.620 gear at 80 MPH.  It might be sluggish at 60 MPH but
there's not much difference in RPM between the three gears at that
speed so I'm leaning towards the 0.620 gear.  I can always drop
back to 4th at 60 MPH which would be 2745 RPM.  Any thoughts?

Dan Jones
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