Economy and how it can be improved

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sidewaysste

sidewaysste

Active Member
Posts
715
Location
Nottingham
I've been thinking about how to improve the economy on my Discovery. I can't afford to use it every day as it's never going to be super frugal. It has always been very thirsty though and I'm going to see what I can do to change it from eye watering to just painful, hopefully with real world data and results.

I've got possibly the most inefficient setup possible - V8, 285/75/16 MT, Auto

I'm starting with the simplest of things - tyre pressure. Less rolling resistance has go to be a good thing.

I've removed the CATs to reduce restriction on the exhaust and when funds allow I will fit less restrictive manifolds and a less restrictive system.

I've ordered a pair of electric fans to enable me to remove the huge viscous fan.

Further down the line I aim to accurately tune the fuelling and ignition maps for efficiency.

I currently get between 10 and 12 MPG with, on one exceptional run towing at a steady 55 mph 16mpg.

It would be nice to be able to make the torque converter lock up at lower speeds.

Your thoughts would be most welcome...
 
10 to 12 mpg is very low. I have a '95 3.9 auto which is absolutely bog standard and regularly achieve 14-16 mpg in general local use; no long runs involved.
 
Sell it and buy a tdi, or sell it and buy something else to use every day. If you need to space go for an estate. Audi, Mondeo, etc....

Either way Discoverys are 2.5 ton bricks.
 
That is on LPG. To sell it is missing the point. I have other vehicles, but I'm wanting to see what can be done with this. I doubt a Tdi would work out any cheaper - diesel's bloody expensive!
 
It's an expensive route to try and shave a few mpg off the consumption.

New headers, aftermarket ECU so you can remap yourself, locked torque converter, etc etc. Cheaper to get a diesel in the end.

After all with LPG you are getting the equivalent to 24mpg so not too bad. As mentioned before it is a heavy car and not built for economy. What exactly did you expect when you brought it?
 
I'm gonna find a brick wall in a minute! I know it was never going to be cheap, I know experimenting isnt cheap, but that's the point of the experiment, to find out which modifications will pay for themselves and do help economy so that other people can improve their V8s.
 
the tyres won't help that much i've got 33x12.5 r15 mt's and they suck power which inturn mean more fuel usage on my 300 tdi. So why not try smaller wheels or even at's, secondly regular servicing may well help you out. You are on the right track with tyre pressures as these can have aa effect. Make sure that non of your brakes are sticking on, and also that the handbrake isn't sticking. check your wheel bearings to make sure they are smooth in running and not notchy, check gearbox/transferbox, and diff oil levels, what i'm saying is to start at the basics. I don't think you will attain an mpg figure over 16-17mpg but if you want to spend the cash try it
 
I know the tyres don't help. That's something I have to accept though as I need them for the type of use it gets. The basics have already been done.
 
Hi there sideway, I'm a bit confused on what is your objective here -are starting an unlimited budget experiment or do you want to cut your running costs?

If we look at your stated fuel consumption of 10-12 mpg and factor in that she's running on lpg already (I think??) and assuming that lpg in the uk is on average £0.7497 over the last ten days according to this site: http://www.landyzone.co.uk/lz/newreply.php?do=newreply&noquote=1&p=2397639

and petrol (95 unleaded) is £1.3594, according to this site: Free UK fuel prices. Over 11,000 petrol stations covered - PetrolPrices.com

Then you have costs:

1000 mls at 11 mpg costs on petrol = £561.31

1000mls at 11mpg costs on lpg = £309.54

So lpg is 45% cheaper. That means that the equivalent mpg 11/0.55 = 20 mpg not 24.

Plus this assumes that you use lpg for every second the engine is running, which I believe is not the case on these installations.


So now considering your proposed 'efficiency' modifications:

A new set of headers (exhaust manifolds) to breath better - £300 ish

A new freer flowing exhaust system - £500??

A modified torque converter - £300 plus fitting


So let's round that up to £1000 - what improvement would you expect to get? 10%? 15? Let's work on 15%, so every 1000 you would save about £46 on lpg. So your investment would pay for itself in 20,000, roughly.

However, if you bought a decent TDi 300, for about £1500, serviced it fully you would expect to get 30mpg from day one. PLus you would still have something worth £1500 whereas your £1000 worth of mods are devalued to perhaps £300 as soon as they go on the car.

As I said at the beginning if you are attempting an efficiency project with no budgetary constraints just see what what can be done, then go ahead and share your results with us when you have them.

However, if your primary goal is to reduce your daily costs - get a diesel.

My last TDi 300 auto averaged 33mpg over 16,000mls - including trips to the Sahara and Safeways.

Dave
 
It's more an experiment to see what gains can be made and what are the most cost efficient ways of doing so. I'm under no illusions that it will save me money in the short term.
I doubt the differences with the Tdi would be as big for me as you say though.
It would be an assumption to say that I could expect 30mpg from day one. Who's to say that a V8 in the same spec as your car driven by you wouldn't do significantly better mileage than mine does for me?
My style of driving and use may be very different from yours which would make a comparison impossible. For instance I know my disco will average 16mpg over 400 miles pulling a boat trailer. My Dad's Audi A6 3.0 Tdi quattro would average 22mpg pulling the same trailer over the same distance. Unloaded that car is capable of 40mpg. I very much doubt a heavier car with worse aerodynamics would better those figures in those conditions.
 
I get what he's doing .. He has a vehicle he likes, he has an engine he likes, he just wants to improve the mileage as much as a project as a means to save money .. bit like many of us improving our cars so we can get deeper in the **** before getting stopped!

So it'll cost him, he realises this, so it would be cheaper running a Tdi, he realises this, but he wants to experiment on things, and I applaud him for it! I mean, we're all doing that with different springs, shocks, spacers, tyres, diffs, whatever, he's just doing it with a V8.

Fair play I say ..

Pump tyres up, let 'em down again for offroading.

Empty the vehicle of everything you don't need for that journey .. weight is a killer, though driving a brick through air means most weight hardly matters!

I always found that with a petrol engine the state of the spark plugs, their suitability and heat range are extremely important as is the state of the HT leads.

Make sure the fluids are all in good shape, engine, gearboxes, diff oils, and that you're not over filling anything!

Have fun .. ;)
 
The ignition system certainly takes more looking after than some cars. I've got an OEM cap and rotor arm, Magnecor KV85 leads and iridium plugs i.e. the sort of thing I'd normally use in a particularly fruity turbo engine build....
 
No ones mentioned a good wash and polish :) it always makes a difference especially when you get all that mud from the break calipers and wheel arches, then the polish helps it slip through the air like a slippery thing :D
 
Actually the best thing, I always found for cheapness, is simply making sure airways and exhausts are clear and as clean as can be with blended curves, and no sharp bends where possible. Exhausts, I used to find a lot on bikes, were never correctly sized to the exhaust ports and gaskets often over-sized, so again, blending and cleaning can work minor wonders.
 
Paul D said:
Actually the best thing, I always found for cheapness, is simply making sure airways and exhausts are clear and as clean as can be with blended curves, and no sharp bends where possible. Exhausts, I used to find a lot on bikes, were never correctly sized to the exhaust ports and gaskets often over-sized, so again, blending and cleaning can work minor wonders.
Click to expand...

Agree with above, exhaust gasses need to exit unrestricted without having to be pushed out by the pistons.
Free flowing exhaust, ported like a race engine and leave the inlet alone will give economy.
A cold clean air supply is also vital, colder the better, pipe it in to the air cleaner because cold air is more dense than warm and will improve combustion.:)
 
landowner said:
Agree with above, exhaust gasses need to exit unrestricted without having to be pushed out by the pistons.
Free flowing exhaust, ported like a race engine and leave the inlet alone will give economy.
A cold clean air supply is also vital, colder the better, pipe it in to the air cleaner because cold air is more dense than warm and will improve combustion.:)
Click to expand...

But surely if running a MAF and unless it has ambient temp correction on the ECU it can also make it worse!

The hotwire ECU's work by sensing the voltage/current change in the wire as air passes over and cools the element so a cold day will make the engine less economical as it will put more fuel in in order to match the flow of what it thinks is more air due to the temp
 
Dr_evil said:
But surely if running a MAF and unless it has ambient temp correction on the ECU it can also make it worse!

The hotwire ECU's work by sensing the voltage/current change in the wire as air passes over and cools the element so a cold day will make the engine less economical as it will put more fuel in in order to match the flow of what it thinks is more air due to the temp
Click to expand...


You may be right I dont know, forgot it was on electricery and not carbs, cold air means more compression so bigger bang for the fuel available, unless technology upsets the balance and alters the fueling:rolleyes:
 
landowner said:
You may be right I dont know, forgot it was on electricery and not carbs, cold air means more compression so bigger bang for the fuel available, unless technology upsets the balance and alters the fueling:rolleyes:
Click to expand...

Put it this way my GTi which is much newer than the V8 he has runs better in the middle of summer when the MAF is hot so it fuels lean instead of winter ;) Its got a silly MAF on it -__-
 
As L said, I know next to nothing about the electronics of it, but it makes sense that going back to basics, cleaning air and gas flows makes a helluva difference on many motors. All it costs is time fettling and tuits ... ;)
 
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