[DeTomaso] Taller 5th gear for cruise

Mad Dog Antenucci teampantera at yahoo.com
Thu Jun 17 22:57:46 EDT 2010


Gear Ratio calc's read well in video games ;-]>


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




________________________________
From: Asa Jay Laughton <asajay at asajay.com>
To: detomaso at realbig.com
Sent: Thu, June 17, 2010 1:07:47 PM
Subject: Re: [DeTomaso] Taller 5th gear for cruise

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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