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).

We did the before test this afternoon. We have a nice stretch of a road not far away which is good for testing. It's a straight 14,5-km road with a 0,048% grade (according to local topographical map). It's a 2-lane road but with few traffic. We were never in a vehicle's wake, just some passing cars on the left lane.
First, we filled up to the top at a station and 2 bottles too. We went to the starting point, filled up again the tank to the top and stopped at a mark we could recognize. I throttled at 100% load and shifted at 2000 rpm to reach the cruise speed of 80 km/h on GPS. 300 m before turning to do the other direction, I shut down the engine and EOCed to the stop line to avoid any varying idling time due to passing cars. That distance was subtracted to calculate the consumption. Again, I throttled at 100% load and did the other direction in the same conditions. I shut down the engine again at the end and EOCed to the starting point, distance was subtracted too. The course was recorded with a GPS to know the exact speed. We fillup again to the mark, we put one full bottle (1,00 L) and 28,0 g of the second one. So that's 1033,9 mL (827 g/L at 25°C).

Conditions :
Road : 14,5 km in each direction - 0,048% uphill grade in first NW direction (7 meters on 14,56 km)
Temperature : 25,7°C
Pressure : 1021,1 hPa
Humidity : 43%
Wind speed : 13 km/h NNW (we faced it in the first direction, it's hard to have less wind here)
Sunny
Engine at operating temp
Tire pressure raised to 2,8 bar

Fuel consumed : 1033,9 mL
Distance without EOC : 28,56 km
Consumption : 3,620 l/100 km
Recorded average speed : 80,26 km/h

That is 64.99 mpg at 49.88 mph.

Next week, we will change the cogs and wait for a day with similar wind conditions and do another test.

ABA-ing on short distances is questionnable even if your operating mode sounds bullet proof

Most of the inaccuracy comes from the fillup, be able to refill to the same level. I quickly calculated that a one centimeter level difference is about 0.05 l/100 km on the distance we drove. Level difference was no more than 5 mm.

But I think that 30 km done that way are more accurate than 1000 km. More accuracy on the volume fillup but much more variables that I don't control.

Ideally, I would like to pump the diesel directly out of a bottle I would weigh before and after.

I beg to disagree.
What you're testing this way is the efficiency at a very specific RPM and in specific conditions.

Performing a lot of miles on the other hand is a way to check the mod in various conditions, all in all, real life.

There are ways I can think of to improve mileage in very specific conditions but in real worl driving they end up worst than the factory setup.
Balance is a difficult task.

Yep, that's what I want to test. Gain at a steady 50 mph. Most of our driving is at steady speed at a specific RPM so that test will be interesting to have.
We will see the gains on a tank anyway by driving but we'll have all the other variables : traffic, weather, speed, type of roads...
I probably won't gain as much as in the test since nobody drives 100% in 5th gear. But I'm optimistic for the gains, I'm hoping for 3,30 l/100 km, 3,25 would be amazing.

That will be interesting to be able to categorize the effect of a measured improvement inside everyday use.
Depending on your drive, it could affect the FE in good or bad and if it is good, maybe you will see a return of just a portion of the measured improvement.
I'm looking forward to it.

We did the swap yesterday, everything went fine. To test the gearing, I turned the brake disc and compared to the primary cog (=engine). I got 8 revs on engine = 7 revs on wheel but the other wheel was on the ground so it has to be divided by 2 due to the differential. 8 revs on engine = 3,5 revs on wheel = 0,4375. Theory says 38/25*17/59=0,438. Not bad at all.
We did some stationary tests with one side up. 5th gear works smoothly, brake disc spins really fast compared to 4th gear.
And finally, ultimate test on the road. It was like I expected : nicely high geared but not too much. The engine has a lot of low-end torque so it works great. We'll do the other test next week.
We also plan on mounting an intercooler (which exists stock for the engine) which increases torque from 16 to 18.6 mkg at 2100 rpm. This mod should also increase efficiency.

Pictures : old gears / new gears / before / during / after

http://ecomodder.com/forum/attachmen...9&d=1380058283

http://ecomodder.com/forum/attachmen...0&d=1380058283

http://ecomodder.com/forum/attachmen...1&d=1380058283

http://ecomodder.com/forum/attachmen...2&d=1380058283

http://ecomodder.com/forum/attachmen...3&d=1380058283

Fantastic that it was such a simple swap.

I wish I could do the same for my Firefly (Metro/Swift)... alas, all the gears were the same from different variants. They only used different final drive ratios from model to model.

Looking forward to the final results!

I took the car one week to do a MPG test. I drove at 56 mph average (GPS) on 70% of the commute, the remaining at 45/50 mph. I got an impressive 3,43 l/100 km (3,53 with GPS distance). At same speed and same roads, I made 3,89 l/100 km some time ago but it was in winter and I didn't use as much P&G as now. But still, the 5th gear is doing well. My father couldn't believe it! :D
Tomorrow, we'll do the after test.

What's the "after" test ?

"B" test, rather. The test I made in the second post but with the new gearing.

I corrected the volume of the first test. I took 1,00 L for the first bottle I put but the station volume is not as accurate (only 10 mL) as weighing.

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).

I have also a Citroen AX (Gasoline MY88 AX 954 cm3) and I want to increase gear Ratio.

I see you change your front Tires from 145/70R13 to 155/80R13. I want to do the same with Toyo NanoEnergy 3 155/80 R13 but I was wondering why only in front ? Do you experience some problems when you turn (Friction of the tire against shape ?
Other point I want to change my current 4 speeds Manual transmission with a 5 Speeds one with longer ratio (I'am looking for a MA5/O from a Peugeot 208 1,4l HDI Blue Lion).
According my caculations with those 2 modifications (tires & gearbox) 1000rpm speed (km/h) will be :
I : 8.62 (12x41*17x61) instead of 7.38
II : 16.28 (21x38*17x61) instead of 13.94
III : 25.13 (29x34*17x61) instead of 22.33
IV : 34.51 (41x35*17x61) instead of 30.98
V : 43.27 (47x32*17x61)

Do you experience some driveability issues with such ratio ?

Thanks by advance for sharing your experience.

I wouldn't want to be a pain but are you sure the gearbox would work in your application ?
It's been a lot of time since the AX era and a gearbox mated to today's 1,4 HDi is probably a stronger unit than the one you had in your car.

That being said I once fitted the diff of a diesel variant in my 1981 Mk1 Golf GTi to good effect.

I have the same doubts. Even if the 1.4 HDI's gearbox is still a "MA" type like the AX, I believe that there have been some modifications since. I have only seen the MA/5O gearbox on pics and from what I could see the body is not exactly the same so I'm not sure if the holes for the screws are exactly in the same position. The best is to see the gearbox before you buy it and check.

Secondly, that gearing will be way too high for that low torque engine (75 Nm at 3700 rpm). I have 44,7 km/h/1000 rpm but with an engine that has 25% more torque than yours (97 Nm at 2250 rpm) and at lower rpm which means that it has around 40% more power at 2000 rpm. And it is already quite borderline, it's fine for highway cruising but I have to mash (80%) the throttle on 3% inclines to keep 90 km/h. I increased ratio by 19% and top speed dropped to 140 km/h. What you want to do is +40%, I think the 5th gear will be undriveable with top speed no more than 110/120 km/h on flat and without wind.
Try the diesel gearbox (after 92), it has 20% higher ratio (43x33 and 17x61), that should be enough.

As for the tires, I mounted them only on front because :
- it's a front wheel drive so you only need them on the front to have a bigger gearing, I have no driving issues with having different sizes on front and rear, it's just 5,7%.
- they don't fit at the rear anyway (I have only 2,5 cm free with stock tires and the 155/80 would probably rub on the body)

You don't need to put bigger tires. You have enough room for improvement on the gearbox ratio to keep the original size. It's always better to keep the lowest tire size, less rotational weight, and change the gearbox. I have some good experience with the Yokohama Bluearth which exists in 145/70.

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)

I Have kind of the same experience :

I fitted a diesel diff in my Mk1 Golf GT1.
Top speed took a hit since the car was barely able to pull peak torque in top gear but this was 4500 rpm @ 180 kilometers an hour.

I've fixed your account so you can post photos now.

Bienvenue a EcoModder! Welcome to the forum.

Thanks MetroMPG allowing me to illustrates my projects.
You will find below the sketch to jump from MA4 -> Last release MA5O.
http://ecomodder.com/forum/member-mo...box-change.jpg
The potential effect in fuel economy of such a gear ratio change on a Citroen AX :
http://ecomodder.com/forum/member-mo...-ma4toma5o.gif
Same fuel economy graph potential with AX 1,5 D MA5L Gear ratio instead of AX 1.0E MA4.
http://ecomodder.com/forum/member-mo...e6258-ma5l.jpg
And finally my project road map overview to reach the 3l/100 km target on my Citroën AX starting from a current 4,9 L/100 with lowering idle speed to 650 rpm.
http://ecomodder.com/forum/member-mo...ll-whiteax.jpg

Thanks to Ecomodder, I earn that with an EOC kill Switch we can decrease fuel consumption. I'am currenty adapting such a switch on my car (very simple on an cabureted engine like mine). I will give you a feed back soon.

toyota starlet 5th gear swap
 

I am considering swapping the 5th gear on our 1996 Toyota Starlet with a 1.3 2E-E engine (C-150 gearbox?) for a 5th gear of a Starlet 1.5 diesel or a Starlet Turbo (C-153 gearbox?) The rpm of the engine is almost 4000 at 120 km/h, but the motor feels strong enough (it's a light car) to have a taller 5th gear. According to Wikipedia the current 5th gear is 0.815 and for the Starlet Turbo gearbox 0.725. Theoretically the rpm would then be 4000/0.815*0.725=3558 rpm, which is stlll quite a lot. Does anybody know whether these 5th gears can be swapped? Or any other options?