Fiat Dino 2 Litre rear axle ratio exchange
Posted: Sun Sep 15, 2019 2:35 pm
When cruising your Fiat Dino in 110 - 120 Km/h, you probably are in a constant search for a 6:th gear...
If you own a 2 Litre Fiat Dino, there is no "long 5:th gear option" to install, like the alternative 5:th
gear set for the 2,4 Litre/ZF Dino.
I have now finished a project which maybe could be of interest for the members of the Forum: an
exchange of the original 2 Litre Dino 8:39 rear axle ratio, to a 10:43 gear ratio.
This raises the speed with around 13,3 %, at given engine rpm, in all gears. (The ZF "long 5:th gear"
raises the speed with around 9,5 %, at given engine rpm - but in 5:th gear only, of course.)
At first, I was concerned the lower gears would be all "too high" - too much affected. Fortunately, I
soon realized that the lowest gear always is the least affected, when changing the final gearing - and
vice versa. For the detailed outcome - see the diagram table below.
BLACK lines = 8:39 RED lines = 10:43
When driving in 1:st or 2:nd gear, you probably will not notice any changes at all. An up-change to 3:rd,
and you will notice it is "a little longer". 4:th gear now is very close to the original 5:th, and the 5:th
gear now has become the overdrive 5:th you always have been missing...
The engine handles all this effortless. Personally, I can´t understand why FIAT did not choose this (or a
similar) gear ratio for the Dinos. The car´s 0-100 Km/h performance seems unaltered, as you now can
reach 100 Km/h without a second gear change up to 3:rd gear. See the diagram table.
Top speed? I have not been able testing it, but it ought to be in the 210 - 220 Km/h range. The main
enemy here is the air resistance - when you double the speed, the air resistance goes up by four times!
The last step in this project was a re-calibration of the speedometer. This demands some special tools,
so I turned to a local car instrument shop, to have this properly done.
Dinoswede
If you own a 2 Litre Fiat Dino, there is no "long 5:th gear option" to install, like the alternative 5:th
gear set for the 2,4 Litre/ZF Dino.
I have now finished a project which maybe could be of interest for the members of the Forum: an
exchange of the original 2 Litre Dino 8:39 rear axle ratio, to a 10:43 gear ratio.
This raises the speed with around 13,3 %, at given engine rpm, in all gears. (The ZF "long 5:th gear"
raises the speed with around 9,5 %, at given engine rpm - but in 5:th gear only, of course.)
At first, I was concerned the lower gears would be all "too high" - too much affected. Fortunately, I
soon realized that the lowest gear always is the least affected, when changing the final gearing - and
vice versa. For the detailed outcome - see the diagram table below.
BLACK lines = 8:39 RED lines = 10:43
When driving in 1:st or 2:nd gear, you probably will not notice any changes at all. An up-change to 3:rd,
and you will notice it is "a little longer". 4:th gear now is very close to the original 5:th, and the 5:th
gear now has become the overdrive 5:th you always have been missing...
The engine handles all this effortless. Personally, I can´t understand why FIAT did not choose this (or a
similar) gear ratio for the Dinos. The car´s 0-100 Km/h performance seems unaltered, as you now can
reach 100 Km/h without a second gear change up to 3:rd gear. See the diagram table.
Top speed? I have not been able testing it, but it ought to be in the 210 - 220 Km/h range. The main
enemy here is the air resistance - when you double the speed, the air resistance goes up by four times!
The last step in this project was a re-calibration of the speedometer. This demands some special tools,
so I turned to a local car instrument shop, to have this properly done.
Dinoswede