Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Peugeot 205 5th gear swap (8.2% improvement at constant 50 mph)

HypermilerAX · 09-20-2013, 06:49 AM

My father introduced me to hypermiling 3 years ago and then I discovered ecomodding myself. And now, my father asks me about ecomodding when he saw what I did on my car. He’s interested in having a higher 5th gear on his 205 turbo diesel.
So I did some research about the different gearings on the XU engines. The car has already the longest available differential (17x59) but the 5th gear has room for improvement. Stock gearing is 37x28 and 38x25 is mounted on some other cars with shorter differential. We already have a spare engine which has the gearbox with the parts we are looking for so we have no reason not to do it. The mod is easy to do as it doesn’t require to demount the gearbox. It’s like on mine, just a cover to remove to have access to the 5th gear.

Stock gearing is 40,3 km/h at 1000 rpm and we would have 46,4 km/h at 1000 rpm, that’s 15,1% improvement. The mod should be even more effective considering the fact that the stock 5th gear is not that high. Max speed is reached at max RPM (4300) which means that it’s designed for performance. On my AX, top speed in 5th was reached (before mod) at 4300 rpm whereas max RPM is at 5000 rpm. So the gear was designed for economy and I still had nice improvements so imagine on the 205. His best with no mods at all (not even tire pressure) is 68.2 mpg by driving no faster than 45 mph.

Pictures of mod and results will follow.

EDIT:

Recap :

Before :
Temperature : 25,7°C
Pressure : 1021,1 hPa
Humidity : 43%
Air density : 1,197
Wind speed : 13 km/h NNW
Sunny
Engine at operating temp
Tire pressure raised to 2,8 bar

Fuel consumed : 840 g = 1015,7 mL (827 g/L at 25°C)
Distance driven without EOC : 28,56 km
Consumption : 3,556 l/100 km
Recorded average speed : 80,26 km/h

Corrected consumption (80 km/h and air density 1,2) : 3,547 l/100 km

After :
Temperature : 20°C
Pressure : 1020 hPa
Humidity : 77%
Air density : 1,220
Wind speed : 12 km/h NNW
Clouds but dry road
Engine at operating temp
Tire pressure raised to 2,8 bar

Fuel consumed : 748 g = 901,2 mL (830 g/L at 20°C)
Distance driven without EOC : 27,30 km
Consumption : 3,301 l/100 km
Recorded average speed : 80,23 km/h

Corrected consumption (80 km/h and air density 1,2) : 3,255 l/100 km

Before : 66.16 mpg
After : 72.28 mpg

This is exactly what I expected. It's an 8.2% improvement for a 15.1% higher ratio (MPG gain = 55% of ratio change).

09-20-2013, 06:49 AM	#1 (permalink)
HypermilerAX EcoModding Apprentice Join Date: Apr 2011 Location: Southern France Posts: 159 AX - '95 Citröen AX 307 - '04 Peugeot 307 SW Thanks: 12 Thanked 67 Times in 37 Posts	Peugeot 205 5th gear swap (8.2% improvement at constant 50 mph) My father introduced me to hypermiling 3 years ago and then I discovered ecomodding myself. And now, my father asks me about ecomodding when he saw what I did on my car. He’s interested in having a higher 5th gear on his 205 turbo diesel. So I did some research about the different gearings on the XU engines. The car has already the longest available differential (17x59) but the 5th gear has room for improvement. Stock gearing is 37x28 and 38x25 is mounted on some other cars with shorter differential. We already have a spare engine which has the gearbox with the parts we are looking for so we have no reason not to do it. The mod is easy to do as it doesn’t require to demount the gearbox. It’s like on mine, just a cover to remove to have access to the 5th gear. Stock gearing is 40,3 km/h at 1000 rpm and we would have 46,4 km/h at 1000 rpm, that’s 15,1% improvement. The mod should be even more effective considering the fact that the stock 5th gear is not that high. Max speed is reached at max RPM (4300) which means that it’s designed for performance. On my AX, top speed in 5th was reached (before mod) at 4300 rpm whereas max RPM is at 5000 rpm. So the gear was designed for economy and I still had nice improvements so imagine on the 205. His best with no mods at all (not even tire pressure) is 68.2 mpg by driving no faster than 45 mph. Pictures of mod and results will follow. EDIT: Recap : Before : Temperature : 25,7°C Pressure : 1021,1 hPa Humidity : 43% Air density : 1,197 Wind speed : 13 km/h NNW Sunny Engine at operating temp Tire pressure raised to 2,8 bar Fuel consumed : 840 g = 1015,7 mL (827 g/L at 25°C) Distance driven without EOC : 28,56 km Consumption : 3,556 l/100 km Recorded average speed : 80,26 km/h Corrected consumption (80 km/h and air density 1,2) : 3,547 l/100 km After : Temperature : 20°C Pressure : 1020 hPa Humidity : 77% Air density : 1,220 Wind speed : 12 km/h NNW Clouds but dry road Engine at operating temp Tire pressure raised to 2,8 bar Fuel consumed : 748 g = 901,2 mL (830 g/L at 20°C) Distance driven without EOC : 27,30 km Consumption : 3,301 l/100 km Recorded average speed : 80,23 km/h Corrected consumption (80 km/h and air density 1,2) : 3,255 l/100 km Before : 66.16 mpg After : 72.28 mpg This is exactly what I expected. It's an 8.2% improvement for a 15.1% higher ratio (MPG gain = 55% of ratio change). __________________ Citroën AX 1.5 D 430.000 km Peugeot 307 SW 2.0 HDI 136 195.000 km Last edited by HypermilerAX; 10-06-2013 at 01:54 PM..