[monah78]

Thanks for your advices.

I've made some investigations on the web this week in order to assess mechanical feasability and driveability replacing my current AX 4 speeds gearbox (MA4) with a long ratio one from low consumption version of a Peugeot 208 1,4 HDi BlueLion (MA5O). Let's show the results. From a high level mechanical point of view it seems to be feasable replacing only gearbox itself (tag 1 in red on the picture) and adapting the clutch case from my current MA4 (bottom view) to the MA5O (upper)
Sketch of MA5O vs MA4 : (See in my ecomodder album picture6256-ma-gear-box-change]
Those basic assumptions has to be transformed in reality but hope is remaining !
I will visit next week a "car breaker" who have a gearbox from a crashed 208 1,2 VTi (normally same interfaces) to have a look and confirm if it's really feasible.

The fuel economy potential of such a gearbox switch is amazing. To illustate on a graph that I have plotted in a BSFC=f(Torque, RPM) graph the iso-speed lines corresponding to my AX10E and the effect of the regearing switching from MA4 to MA5/O (See in my ecomodder album picture6255-ma4toma5o)
Estimated fuel economy can rise up to 45% @ 70 km/h (43,5 mph) and 18% at 90 km/h (56 mph) corresponding to an average depending of the use of 20 to 30%.

As you mention the main drawback will be driveability. According my simulations the time to go to 120 km/h starting from 80 km/h on the last gear will be increase from 17s to around 29s !!!. An option will be to decrease gear to 3rd to recover similar acceleration.

Max speed (originally 140 km/h) will not be longer reachable on 5th gear but it seems to be achievable in 4th gear (even 150 km/h) according the graph. This point has to be checked but personally I never overpass 110 km/h => so for me it's not an issue.

For curiosity, I have made the same graph with your diesel gearbox 92 (MA5/L according internet websites). See the graph (in my ecomodder album 'picture6258-ma5l'. The potential fuel economy benefits will be divided by around 2. I will keep this option as a "less critical" and less costly path if my initial idea doesn't finally works.

Finallly let's share the fuel economy target I have with my White Citroen AX 10E "K-Way"
(picture6257-co2-water-fall-whiteax in my ecomodder album)
I will be very interested with your feed back on the other items.

Waiting your interesting comments

Nota : I'm not able to share the link to pictures in my posts due to limitation of ecomodder website (too young and not enough posts since registration to be able to share links)