[DeTomaso] Taller 5th gear for cruise

[Asa Jay Laughton]

Have you tried Lloyd's Gear Ratio Calculator on line:
http://www.rbttrans.com/Gear%20Ratio/page1.php

I guess being in fourth at 60 MPH wouldn't be -bad- but then we have  
to get into the conversation of what the car is most often used for.   
It sounds like a reasonable compromise to me but I'd probably go with  
a ratio that gives me a comfortable rpm in fifth at 70 MPH.  I don't  
get much chance to go faster on the street.

But I'm not an expert either. ;)
Asa Jay


Quoting Daniel C Jones <daniel.c.jones2 at gmail.com>:

> 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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