Hello everybody,

So, this thread is the continuation of my presentation thread I started last year but with all the technical about my mods.

A frenchie here
I called this project "AX Eco", inspired by the prototype that was presented in 1994 by Citroën. The car's mileage was 87,1 mpg at 56 mph (2,7 l at 90 km/h) compared to the production car's figure of 71,3 mpg (3,3 l). I have the post 1994 version which comes out at 65,4 mpg (3,6 l), a bit more than the previous version but due to its major cooling problems leading to head gasket issues, that version was a no-go for me.

The target is to get 90 mpg at 56 mph (2,6 l at 90 km/h), so a bit better than the prototype. If I reach this, it will mean 100+ mpg at 40/50 mph speeds (2,35 l at 70 km/h). Every mod will be translated into a modification of the weigh/CdA/Crr/engine efficiency datas to calculate the theoritical FE at 56 mph. I know this method will not be completely accurate : when I my make a mod the car produces less power and torque (rpm is equal) so the BSFC changes a bit (in the wrong way at low load). But whatever...

I have driven 30.000 miles so far at 77,1 mpg average with a few mods already done.

Here are the official datas (except the Cr I measured experimentally) of the stock car.

Weigh : 805 kg (1777 lbs), + 80 kg for driver and fuel

Cd : 0,31

A : 1,74 m² (18,85 ft²)

CdA : 0,5394 m² (5,844 ft²)

Crr : 0,0109 (Michelin E3B 155/70 R13 at recommended pressure 31,9 PSI)

Engine efficiency : 22,7% (determined with above datas and official FE)

**Measuring fuel flows**
The car has an old diesel engine with no electronic whatsoever. I looked into flowmeter systems like heating oil counters but these were very expensive and I had no remote display. After some searching, I heard of the Zemco system. I grabbed 2 of these, two because I have a return line to the tank. I have yet to receive the second one. I won't have direct display of the consumption but consumptions of each line which I'll have to substract.

My mods will be measured bidirectionnally on a 28-mile distance part of my 43-mile commuting trip at 56 mph constant speed.

**Tires**
For now, I just hyperinflated the tires to the max. sidewall pressure : 44 PSI. Crr drops from 0,0109 to 0,0095.

Measured on a flat road with no wind. 5 measures in each direction for each pressure. Results were 42,17 seconds to coastdown from 16,5 km/h (actual speed when my speedo is at 20) to a complete stop at 31,9 PSI and 48,21 seconds at 44 PSI. Despite being low, my calculations also take into account aero drag (neglect it will slightly overestimate Crr).

**Weight**
Not much here. I removed all the seats I don't need. I always drive alone and I also need the space to carry stuff from time to time. 63 lbs gain.

**Aero**
The mods I have already done are :

-Radio antenna removal

-Right mirror removal

-Front wiper removal (in the car)

-Sealed front gaps

-Partial grill block

-Rear wheel skirts

I calculated the theoretical gain of the radio antenna by multiplicating the measured frontal surface by the drag coefficient of a cylinder. CdA drops by 0,0012 (0,14% better FE).

As for the other mods I will probably measure all together (maybe both fuel flow measurements and coastdown tests to compare) because the effect of each alone is too small.

New data with mods measured so far :

Weigh : 1714 lbs

Cd : 0,31

A : 1,74 m²

CdA : 0,5383

Crr : 0,0095

Engine efficiency : 22,7%

FE at 90 km/h : 3,42 l/100 km (68,8 mpg)

My next (major) mod will be changing the 5th gear ratio. By the end of the year, I hope.