Ducato gearbox/diff ratio

[Portland]

Do we have any Fiat technical people who could give information on this. My van based on a Ducato 3ltre / 6 speed box travels at approx. 58/60 Mph at 2500/2600 RPM. Could I change the diff to improve the MPG by reducing the revs . Also any guides as to a good garage to do it.

 

[Big Lad]

what about considering a plug in chip to give extra low end torque, lower revs and better fuel economy?

 

[tonyidle]

what about considering a plug in chip to give extra low end torque, lower revs and better fuel economy?

You cannot change mph / rpm with a chip. To make best use of extra low down torque you would need to do what the OP is proposing.

 

[pappajohn]

Lower revs, higher mpg.........dont think so.

Lower revs at a given speed will mean the engine is working harder to maintain that speed.

Gear ratios are carefully calculated by men with tall foreheads to maintain a balance between tractability and economy.

The difference btween ratios is akin to a builders pickup loaded with sand and bricks trundling around town and the comparatively lightly loaded delivery van cruising on motorways.
you are the heavy builders pickup cruising on motorways.....higher revs, less work

 

[dave newell]

Not as far as I'm aware of, TBF if your motor is doing 2500-2600 at cruising speed 0f 58-60MPH then its about right for good fuel economy as the turbo will be spinning reasonably well at that speed. Lowering the engine speed will result in low turbo speed=low boost=low torque=poorer fuel consumption. You could get it remapped but I'd suggest you do some deep research into this, many reports of damaged engines on the net after mapping and warranties that are written on tissue paper. Alternatively you might be able to alter your driving style to improve fuel consumption (depends on how you drive really) or you could just accept that you bought a big vehicle that is not as fuel efficient as your every day car.

D.

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[DBK]

Do we have any Fiat technical people who could give information on this. My van based on a Ducato 3ltre / 6 speed box travels at approx. 58/60 Mph at 2500/2600 RPM. Could I change the diff to improve the MPG by reducing the revs . Also any guides as to a good garage to do it.

There's something that doesn't sound right with your figures. Mine has the 3 litre engine although with the comfortmatic 'box but I'm sure it isn't doing anything like those revs at 60. We also have 16" wheels, but I guess they match the diff ratio to the wheel size. I may be wrong but your revs seem too high.

 

[Snowbird]

This maybe a longshot, but IF the van has a towbar fitted, sometimes if the van has been used for pulling a trailer the previous owner will fit lower profile tyres as a cheep way of lowering gear ratios. Get someone to follow you at 50 MPH in a car or use a satnav to get a true MPH. I have known this in the past, especially with German imports from mountainous areas such as Bavaria.

 

[ivorantony]

Admittedly I drive a Renault master 150hp with six speed gearbox
And my normal cruising speed is 62 mph with the revs at 2100,
This is just fractionally below maximum torque and gives me about 28 mpg, for a 3900 kg brick shape A class I consider it very acceptable,

 

[Portland]

Not as far as I'm aware of, TBF if your motor is doing 2500-2600 at cruising speed 0f 58-60MPH then its about right for good fuel economy as the turbo will be spinning reasonably well at that speed. Lowering the engine speed will result in low turbo speed=low boost=low torque=poorer fuel consumption. You could get it remapped but I'd suggest you do some deep research into this, many reports of damaged engines on the net after mapping and warranties that are written on tissue paper. Alternatively you might be able to alter your driving style to improve fuel consumption (depends on how you drive really) or you could just accept that you bought a big vehicle that is not as fuel efficient as your every day car.

D.

Good reply this, however, I'm a very sympathetic driver I have driven from the age of 8 learned in a Bedford truck, and have driven millions of miles always with good MPG. I have talked with the local Fiat garage but they could not say what the gearbox is and have told me to find the stamp on the box so where can I find this because from the top is impossible so I will have to crawl underneath.

 

[tonyidle]

Good thread this because I have a similar problem. My 2005 Hymer B584 Classic (full description in case it makes a difference) is built on a Ducato Maxi chassis. However unless someone can tell me differently Hymer specify 15" wheels (which are on the non-Maxi hubs with a different PCD). At a true 65mph the speedo reads just above 70mph. The engine (according to the fitted tacho) is turning at 3500rpm at that road speed. I would like to fit 16" wheels (with same profile tyres as are on the 15s) to improve speedo accuracy and reduce cruising rpm. I'd welcome comments from other Hymer owners (or Ducato base experts).

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[PeteH]

Any calculation to do with tyres MUST take into account LOAD RATING, some low profile tyres do not have the same load capacity as "Standard" tyres as fitted /recommended by the manufacturer. Be aware.

BTW on a straight road a SAT NAV will confirm the accuracy of the Speedo.? Beware of relying on it in a bend or on a curved track as the "vector" factor corrupts the data. Most speedo`s will register high (like 32 when doing 30). That`s so that the manufacturers cannot be sued for your exceeding speed limits!!!

Pete

 

[TheBig1]

the x250 only has 2 gearbox and axle ratio options. the most appropriate is fitted as standard to coachbuilt motorhome chassis'

 

[Trikeman]

Whoa, not doubting your figures but they seem excessive - engine revs wise I mean.

My 2.8jtd 5 speed at 60 mph is bang on 2000 rpm and torquey (is that a word) as hell and pulls well, hardly loses much on the hills and gives around the 28 mpg - that's freighted and mostly with the toad (mpg info).
Measured against the satnav the speedo is about 0.7 mph out - speedo 60 satnav 59.3 (ish). 16 inch wheels with Michelin Aegis which are quite high walled tyres.

Lordy, your clutch isn't slipping is it?

Regards,

Trikeman.

 

[taffybloke]

My PVC 3.0 on 15" wheels shows about 70 at around 2000 revs (shows 65 on satnav) and max torque is 400 nm at 1700 revs. It was a white van man motor for the first couple of years of its life so was probably geared for this but I feel a bit to high for a camper but it makes it a very lazy drive.

I have had it show 42mpg on the display but calculated to 36 on a fill to fill. I have weighed it with full fuel, water and me at 3.0 ton

 

[mitzimad]

the cost of getting a dif supplied and fitted by a main dealer will probably cover your fuel costs for ten years

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[tonyidle]

Whoa, not doubting your figures but they seem excessive - engine revs wise I mean.

My 2.8jtd 5 speed at 60 mph is bang on 2000 rpm and torquey (is that a word) as hell and pulls well, hardly loses much on the hills and gives around the 28 mpg - that's freighted and mostly with the toad (mpg info).
Measured against the satnav the speedo is about 0.7 mph out - speedo 60 satnav 59.3 (ish). 16 inch wheels with Michelin Aegis which are quite high walled tyres.

Lordy, your clutch isn't slipping is it?

Regards,

Trikeman.

No the clutch is fine. I should probably check out the tacho. The engine does sound busy at 65 though. Mine is on 15" wheels.

 

[jongood]

This MPG issue really shouldnt matter for most motorhomers

5000 miles pa seems to be fairly typical motorhome use
The difference between 25mpg and 30mpg is about £175 PER YEAR.

IMHO depreciation and repairs/maintenance are a much bigger figure than fuel cost differentials.

Buy the Motorhome you want/can afford - and enjoy it to the max

Jon

 

[jonandshell]

The tyre size fitted will make no difference on this case.
The speedometer will indicate speed based on wheel rotations. Admittedly, the actual speed would be lowered by smaller, incorrect tyres having been fitted but the INDICATED speed will be consistent with the engine speed, whatever tyre may or not be fitted.
This is either an electronic speedometer calibration issue or simply low gearbox ratios.
I am not sure about Fiat van ECUs , but on our range of forktrucks, the speedo is adjusted for different wheel sizes.
If a customer complains his truck is too slow, you simply fool him by setting a larger wheel size! The speedo will then show the truck is going faster for the same maximum motor/engine speed!

 

[rolandrat]

Taffybloke is correct in what he says about his motorhome. There are 2 distinctive final drives that I'm aware of as I used to own 2 previous 3 ltrs which cruised at 60mph with 1700 revs showing and were very economical. My present one is another 3 ltr coachbuilt Comfortmatic and it cruises at 60 mph with 2000 rpm showing. The drive surprisingly is far better and acceleration is very responsive. I'm also aware that it only slightly less economical. It is running on 15 inch wheels. This one will be far happier touring Spain and Portugal up and down those mountains with far less gear changes.

 

[Lenny HB]

As Big 1 says different ratios for different jobs, if you have a CB built on a chassis cab rather than the Camping Car chassis it will have higher rations. Also the later Euro 5 X250's & x 290's have higher gearing.

As you are driving about in a Motorhome worth 10's of thousands of pounds does it really matter if it does 25 or 28 mpg, the cost of fuel is insignificant compared to the cost of the van.

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[PeteH]

Is the OP looking for better fuel economy? or a reduction in engine noise in the cab?.

The former is largely dependant of the right foot. The later Might be reduced by the use of sound deadening material in strategic Places?.

Edit. OK went back a re read the post, He`s after better MPG. Which IMHO benefits most from a light right foot, Reduction in Mass, Correctly inflated tyres of the right type, removal of "top boxes" etc; Otherwise Newton Rules OK!!

Pete

 

[tonyidle]

The tyre size fitted will make no difference on this case.
The speedometer will indicate speed based on wheel rotations. Admittedly, the actual speed would be lowered by smaller, incorrect tyres having been fitted but the INDICATED speed will be consistent with the engine speed, whatever tyre may or not be fitted.
This is either an electronic speedometer calibration issue or simply low gearbox ratios.
I am not sure about Fiat van ECUs , but on our range of forktrucks, the speedo is adjusted for different wheel sizes.
If a customer complains his truck is too slow, you simply fool him by setting a larger wheel size! The speedo will then show the truck is going faster for the same maximum motor/engine speed!

True but if the speedo says 70mph at, for example 2500rpm, and the the vehicle is actually travelling at 65mph then altering road speed to, say, 70mph by increasing wheel diameter will mean that engine rpm will still be at 2500rpm until road speed is reduced by slowing the vehicle back to 60mph. At which point engine rpm will be lower by the ratio between the two different rolling circumferences.