[DeTomaso] Taller 5th gear for cruise
Asa Jay Laughton
asajay at asajay.com
Thu Jun 17 16:07:47 EDT 2010
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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