best I can get is 41mpg - the engine is loose at 124,000, but more usually 34-38mpg. I wondered about ditching the drive to the rear wheels?

then why did you buy a 4x4?

best I can get is 41mpg - the engine is loose at 124,000, but more usually 34-38mpg. I wondered about ditching the drive to the rear wheels?

Other than the weight saving, you'd get next to no benefit from that. The Haldex only connects the RWD when it's needed.

but it does run the transfer box, prop and input side of the rear diff at all times Ken

so a half decent weight saving and then dropping the transmission loses by probably 15% or so would certainly increase mpg, but its a stupid idea.

A four wheel drive, petrol, turbocharged car - you really are asking a question akin to 'how can I make my QE2 cruise liner handle well' or 'how can I make my tractor go faster on the motorway' ie - your vehicle is the wrong one for this application!

But if you really want to do this,

a) you'll need to drive it half as fast as a 1.9tdi, you may just get half the fuel economy of a tdi when you do this. Drive briskly (accelerate through the gears, do 90mph) and you'll get down to the low 20's, compared to a tdi's 55mpg driven in this manner.

make sure everything is perfect, well serviced, no engine undertrays missing etc.

c) run high tyre pressures, watch for less grip in the wet, go around 36psi front.

d) change the wheels and tyres for narrower ones, as narrow as you can BUT make sure the overall diameter is the same (you'll probably have to go down a wheel size to acheive this)

e) make a full flat underbody cover for your car. Something like half the wind resistance comes from the awful underbody which is akin to a few wheel barrows full of scrap metal under there, not smooth or flat. You can make and fit flat covers to box the whole of the under car in. You'll probably need to change the exhaust and heat wrap is or it will get too hot when boxed in.

f) disconnect the rear drive/change back to a 2wd gearbox. 4x4 wastes a good bit of friction turning that extra diff, prop, diff, hubs.

g) Remap the car with an economy remap where the tuner is skilled and sets the vehicle up with maximum economy in mind.

h) get rid of the cat, the EGR, Air pump etc etc. This may cause issues at MOT time but will give extra MPG.

Or just buy a tdi and get double your mpg. If you want power as well a PD130 with a front mount intercooler fitted and a PD150 (vnt17) turbo fitted and a remap will make around 200bhp and about 50% more torque than a VRS.

Greg.

Hi all,

Just bought a 2002 green octavia 1.8t 4x4 estate last month for the family part exchanging my fabia vrs got just under 43000 miles on the clock.

Just wondered what modifications are best for saving fuel costs with prices rocketing an all.

Are you saying the rear hubs are not connected to the drive shafts and rear diff unless the haldex wants it to?

Because the systems I have mainly come across are pretty much a gimic, the diff doesn't put power to the rear, but the rear wheels still turn the shafts, rear diff, prop etc - so overall the 'drag' on the vehicle is about the same as that power is just put down by the front wheels (like pulling a trailer).

The only real efficient 4x4 transmissions are ones that have both a selective diff where it can disengage power to the rear AND freewheeling hubs, which disconnect the driveshafts. The entire drive train then doesn't turn while driving along, common on some jap 4x4's for the front drivetrain on pickups - that way similar (though bit more weight) to a 2wd for driving around/economy, but if you get stuck in a field you can engage the hubs and the diff and you are in 4x4.

Greg.

Other than the weight saving, you'd get next to no benefit from that. The Haldex only connects the RWD when it's needed.

So what people are saying is that you might as well replace a Haldex with something like a central VC, and save on both cost and complexity?

It wouldn't be worth changing it, it's just not significantly better with regard to economy. As the front is the main drive train, and likely stronger, than the 'afterthought' rear, it does enable the car to be essentially front wheel drive with regard to putting power down unless there is a problem, so this is a useful feature of it.

But for saving economy, nope - unless you have freewheeling hubs it won't really help.

Greg.

So what people are saying is that you might as well replace a Haldex with something like a central VC, and save on both cost and complexity?

A four wheel drive, petrol, turbocharged car - you really are asking a question akin to 'how can I make my QE2 cruise liner handle well' or 'how can I make my tractor go faster on the motorway' ie - your vehicle is the wrong one for this application!

But if you really want to do this,

a) you'll need to drive it half as fast as a 1.9tdi, you may just get half the fuel economy of a tdi when you do this. Drive briskly (accelerate through the gears, do 90mph) and you'll get down to the low 20's, compared to a tdi's 55mpg driven in this manner.

make sure everything is perfect, well serviced, no engine undertrays missing etc.

c) run high tyre pressures, watch for less grip in the wet, go around 36psi front.

d) change the wheels and tyres for narrower ones, as narrow as you can BUT make sure the overall diameter is the same (you'll probably have to go down a wheel size to acheive this)

e) make a full flat underbody cover for your car. Something like half the wind resistance comes from the awful underbody which is akin to a few wheel barrows full of scrap metal under there, not smooth or flat. You can make and fit flat covers to box the whole of the under car in. You'll probably need to change the exhaust and heat wrap is or it will get too hot when boxed in.

f) disconnect the rear drive/change back to a 2wd gearbox. 4x4 wastes a good bit of friction turning that extra diff, prop, diff, hubs.

g) Remap the car with an economy remap where the tuner is skilled and sets the vehicle up with maximum economy in mind.

h) get rid of the cat, the EGR, Air pump etc etc. This may cause issues at MOT time but will give extra MPG.

Or just buy a tdi and get double your mpg. If you want power as well a PD130 with a front mount intercooler fitted and a PD150 (vnt17) turbo fitted and a remap will make around 200bhp and about 50% more torque than a VRS.

Greg.

Appreciate that the 4x4 is not bought for ecomony; cheers for your reply I was just thinking that with a car like this there might be things you could do to save on the fuel & most of the the replies have answered this:)

I mainly bought the car as a option to the VRS; I guess grunt is more important to me than ecomony but there is no harm in trying to save a couple of pennies

It wouldn't be worth changing it, it's just not significantly better with regard to economy. As the front is the main drive train, and likely stronger, than the 'afterthought' rear, it does enable the car to be essentially front wheel drive with regard to putting power down unless there is a problem, so this is a useful feature of it.

But for saving economy, nope - unless you have freewheeling hubs it won't really help.

Greg.

I meant that from a technical PoV a Haldex doesn't really do anything a VC can't do lighter, simpler, and with less servicing. I wasn't suggesting the swap was worthwhile if you had a working Haldex.

Wear the rear drivetrain less and keep the balance of power front biased? That's about all I can think of, essentially you are correct, a Haldex doesn't actually do much other than lock the front and back without a diff, only if the wheels are spinning.

Greg.

I meant that from a technical PoV a Haldex doesn't really do anything a VC can't do lighter, simpler, and with less servicing. I wasn't suggesting the swap was worthwhile if you had a working Haldex.

SAFED - Entry learn to block change up as well as down, plan well ahead, use cruise control and avoid harsh braking. there are a few good pdf's on that site and also look at something like the IAM or ROSPA for more tips. also try to keep your revs to around 2k too.

SAFED - Entry learn to block change up as well as down, plan well ahead, use cruise control and avoid harsh braking. there are a few good pdf's on that site and also look at something like the IAM or ROSPA for more tips. also try to keep your revs to around 2k too.

You mean that, other than those who insist on "driving to pass their tests", there's anyone who doesn't block shift up and down!?

Whats block shifting:O

block shifting going up like 1-3-6 or 1-2-4-6 and down like 6-2-1 etc. i find my 2.0 copes well with block changing and i can get quite could mpg too compared to 1-2-3-4-5-6 by block changing and also reading the road ahead and taken appropriate action before it i.e. let off gas and roll up to hazzard.

block shifting going up like 1-3-6 or 1-2-4-6 and down like 6-2-1 etc. i find my 2.0 copes well with block changing and i can get quite could mpg too compared to 1-2-3-4-5-6 by block changing and also reading the road ahead and taken appropriate action before it i.e. let off gas and roll up to hazzard.

Ah cool I already do that :D 1st to 3rd to 5th

Drive everywhere at 40 like most do round here