raise cruising speed ?

[woodchip40]

hi, i have got myself a smiley face 2.5td 1999 welfare bus. i am converting it to a camper. my main gripe is the cruising speed. i would like to cruise at 70mph but it is happier at 60mph where the fuel consumption is better. with the amount of driving i intend to do each day that extra 10mph would be really usefull. i would like to know if there is an economical way of increasing the cruising speed and dropping rpm.
it runs on 15" wheels ( twins at rear), is it possible to put 16" on all round as i see later transits have these but i don't know if the pcd and hub hole are the same.
what about a different diff ?
is there an overdrive or 6 speed box available.
any advice greatly received. dave.
p.s. it would be nice to keep up with those mercs and vw's !

[dibs]

You could change the back axle for a better diff ratio. Post you reg here http://fordtransit.org/forum/viewtopic.php?f=5&t=37058 someone will be able to tell you what ratio you currently have. Or you can read your vin plate it will give you the gear box type too.

These are the ones available:

Box 7 Diff ratio (see http://fordtransit.org/forum/viewtopic.php?f=31&t=10363 for where to find this box)

G - 4.63 - good and easy one to find
J - 5.14
K - 5.83 (slowest)

N - 4.11 (fastest)
L - 4.56
P - 5.13


Mine is a 2.5 100ps TD with a 4.63 diff and will go 87mph but economy much better at 60

[MinorMatt]

4.63 diffs arnt easy to find...

they are out there but I was looking for 18 months before I gave up

[dibs]

Oh, I thought the 4.11 was the hardest one to find
Did you find out what you've got Woodchip?

[woodchip40]

thanks for the info. my diff is letter 'j' so is 5.14. the vehicle is rated 3995 kgs but i will be running it lighter as a camper. at the moment it almost seems to have too much low down power and easily climbs hills in 3rd. i am sure i can sacrifice a bit of this performance to increase cruising speed.
p.s. no one has said if changing wheels to 16" is a good idea or not ? dave.

[captain hook]

[quote="woodchip40"]thanks for the info. my diff is letter 'j' so is 5.14. the vehicle is rated 3995 kgs but i will be running it lighter as a camper. at the moment it almost seems to have too much low down power and easily climbs hills in 3rd. i am sure i can sacrifice a bit of this performance to increase cruising speed.
p.s. no one has said if changing wheels to 16" is a good idea or not ? dave.[/quote

Just a thought but....

Unless you passed your driving test before 1997 you can't drive a 3995 gross Transit.

The Max speed limit is 60mph for your van....

As for 16" Wheels they will fit but the tyres are a lower profile so....

The Diameter will be the same unless you get higher profile tyres too!

[dibs]

Best thing is to change to 4.63 diff if you can find one. It will reduce your revs by 10%, so 3000rpm will be about 2700 so 60mph will become 66mph or (or 2400rpm and 60mph = 72mph with a 4.11 diff) . I don't think it will translate to 10% better fuel economy though (but could be wrong, which I'm sure someone will point out!)

[woodchip40]

hi again. the plot thickens...... i got the 'etis' report and something strange going on there ( see my other post, page 68 in 'etis' pages) the reg number is different but everything else matches. i can only assume that the company doing the original conversion got the reg. muddled up with another vehicle from day 1. anyway i digress, the etis says i have the 4.63 diff. already and not the 5.14 that it says on my vin plate. what do i believe and what do i do now ???

[dibs]

Sounds a little odd Good luck getting to the bottom of that! Do you have the log book yet?

Have a look for the little metal tag which should be attached to one of the bolts on the diff. That will have the ratio stamped on it. Sometimes a bit rusty and hard to read though, that's if it's there at all.

[woodchip40]

hi again, i've taken a little while in commenting on this thread but i thought i would update you. so far i have done nothing about this speed ratio thing but i have looked into someting else. i am now making my own bio-diesel to use and not my original thought of vegetable oil. i discovered i had a lucas pump and this can't take the strain of even heated veg oil. so bio-diesel it is.
i like this welfare size bus so much i bought another almost identical one. this is the interesting bit - i found it had a ,ERSL,(electronic road speed limiter) these can be reprogrammed to a higher speed so that is what i am going to do for this one. i will now look for a similar unit on the other one and let you know.

[sideshow_bill]

thanks for the info. my diff is letter 'j' so is 5.14. the vehicle is rated 3995 kgs but i will be running it lighter as a camper. at the moment it almost seems to have too much low down power and easily climbs hills in 3rd. i am sure i can sacrifice a bit of this performance to increase cruising speed.
p.s. no one has said if changing wheels to 16" is a good idea or not ? dave.[/quote

Just a thought but....

Unless you passed your driving test before 1997 you can't drive a 3995 gross Transit.

The Max speed limit is 60mph for your van....

Once its converted to a camper (Motorcaravan) Im pretty sure it is 70MPH - may be plans afoot to slow us down further, no way around improving fuel economy at high speed short of drastic streamlining. Its the wind resistance that saps the fuel at high speed.