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Slavs

Crunching Numbers - Gearhead Style

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(edited)

I’ve been doing some gear crunching using an online calculator and comparing different gear  and transmission ratios, tire diameters and their effects on speed and rpms.

http://www.jawsgear.com/calculators/

The results are quite telling and interesting and sometimes surprising. I’ve always thought that the Neu Klasse cars were under geared, but not really. Their overall tire and wheel diameter is 2” or about 10% greater from that of the 1600-2002. A NK car equipped with a 4.10 or 3.90 gear ratio will cruise along at 80mph at nearly the same rpm as an 02 with a 3.64 and stock or nearly stock diameter tires.

The stock 175/82 x 14” tires of the NK have a diameter of 25.3”

The stock 165/80 x 1”3 tires of the 2002 have a diameter of 23.39”

The 185/70 x 13” tires have a diameter of 23.2” (very close to stock)

 The 205/60 x 13” tires have a diameter of 22.7”

 

 

( 4 speed cars with 1.0 ratio in 4th gear)

 

A NK car equipped with a 4.10 diff and 175/82 x 14 tires ”will cruise along at 80mph at 4,356rpm in 4th .

A NK car equipped with a 3.90 diff and 175/82 x 14” tires will cruise along at 80mph at 4,144rpm in 4th .

A NK car equipped with a 3.64 diff and 175/82 x 14” tires will cruise along at 80mph at 3,867rpm in 4th.

 

 

A 2002 equipped with the 3.64 diff and 165/80 x 13” tires will cruise along at 80mph at  4,183rpm in 4t .

A 2002 equipped with the 3.64 diff and 185/70 x 13” tires will cruise along at 80mph at  4,217rpm in 4th  .

A 2002 equipped with the 3.64 diff and 205/60 x 13” tires will cruise along at 80mph at  4,310rpm in 4th 

 

A European Spec 2002tii with the 3.45 diff and 165/80 x 13" tires will cruise at 80mph at 3,965 rpm in 4th.

 

(5 speed 245 overdrive cars with .81 ratio in 5th)

 

A 2002 equipped with a 3.64 diff and a 245 5 speed overdrive transmission and 165/80 x 13” tires will cruise at 80mph in 5th at 3,388 rpm  

A 2002 equipped with a 3.64 diff and a 245 5 speed overdrive transmission and 185/70 x 13” tires will cruise at 80mph in 5th at   3,416 rpm

A 2002 equipped with a 3.64 diff and a 245 5 speed overdrive transmission and 205/60 x 13” tires will cruise at 80mph in 5th at 3,491 rpm

 

 

A 2002 equipped with a 3.90 diff and a 245 5 speed overdrive transmission and 165/80 x 13” tires will cruise at 80mph in 5th at  3,630rpm in 5th.

A 2002 equipped with a 3.90 diff and a 245 5 speed overdrive transmission and 185/70 x 13” tires will cruise at 80mph in 5th at 3,660 rpm.

A 2002 equipped with a 3.90 diff and a 245 5 speed overdrive transmission and 205/60 x 13” tires will cruise at 80mph in 5th at  3,741 rpm.

 

 

A 2002 equipped with a 4.10 diff and a 245 5 speed overdrive transmission and 165/80 x 13” tires will cruise at 80mph in 5th at  3.817 rpm.

A 2002 equipped with a 4.10 diff and a 245 5 speed overdrive transmission and 185/70 x 13” tires will cruise at 80mph in 5th at  3.848 rpm.

A 2002 equipped with a 4.10 diff and a 245 5 speed overdrive transmission and 205/60 x 13” tires will cruise at 80mph in 5th at   3.933 rpm.

 

 

Conclusion:

The addition of the 245 5 speed overdrive with the 3.64 diff will shave off 700-800 rpm (depending on tire diameter) in comparison to stock set up on an 02.

The addition of the 245 5 speed overdrive with the 3.90 diff will shave off 450-550 rpm (depending on tire diameter) in comparison to stock set up on an 02.

The addition of the 245 5 speed overdrive with the 4.10 diff will shave off 250-360 rpm (depending on tire diameter )in comparison to stock set up on 02.

The addition of a 3.45 diff with a 4 speed stock transmission will shave off 100 - 200 rpm (depending on tire diameter) in comparison to stock set up on 02.

If you have an NK car and install a 3.64 longneck diff from a 68-mid 69 2002, you will cruise at about the same rpm as the 02 guys who run the 245 5 speed overdrive with the popular 3.90 diff ratio. And even with the stock 4.10 or 3.90, you’re not that bad off.

And for the 02 guys, is it really worth it to install the 3.90 diff and 245 5 speed overdrive just to shave off 500rpm at top gear ? If you use the 4.10, you’ll be just about back at stock. With both the 3.90 and 4.10, you really shorten 1st and 2nd, rendering 1st almost useless. It only seems to make sense if you retain the stock 3.64 diff, but how well will your car pool in 5th ?

Edited by Slavs
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