[DeTomaso] Taller 5th gear for cruise
Daniel C Jones
daniel.c.jones2 at gmail.com
Thu Jun 17 15:41:09 EDT 2010
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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