There seem to be endless threads on fuel economy but here we go again. I am toying with fitting a 3.9 litre injection v8 into my fairly standard defender 90. I will assume 15-18mpg is about as good as I can expect straight out the box, for normal road driving say between 55 and 60mph.

With a decent tune and megajolt or maybe basic megasquirt, with cruise afr's at say 16:1 would it be realistic to obtain 20 +mpg, or without going fully sequential is this out the question?

Other options of course would be to fit a lpg kit, and maybe megajolt to switch between gas and petrol ignition maps, not to mention improve the overall running anyway.

The target is to achieve a comfortable 25mpg, not driving like a grandad etc. or the equivelent in cost on gas, otherwise it really is out the question due to the milage I cover.

Currently running Grabber 265 AT2 tyres, but would probably change to grabber TR's as they look like they should have much less rolling resistance.

Thanks

James

If you fit multi-point lpg injection, you should get 15mpg or more on gas which equates easily with your 25mpg equivalent on petrol with gas at 73p a litre.

Always try and keep your original tankage (petrol) as a backup for when you run out of gas.

I wouldn't bother with using anything else other than the standard sensors/controls and ECU.

Peter

Not sure if its possible but you could try programming the original ECU to run on half cylinders if at idle for more than 10 seconds like the Audi's do, that'd save fuel round town if you were at lights or waiting in a carpark

Is it for FUEL economy, or general economy.

My opinion has alsways been to just stay on petrol. Any installation for gas would, for me, take 2-3 years comstant gas use to earn it back.

That is that the installation works perfect and no problem or additional service is required for your gas installation. Plus you need a gas supplier near, else the extral mile to get it doesn't economise.

And when you need serious power ( that's why it is a V8 and I have one for the experience as well ) you need petrol anyway.

I set my V8 at 2500-3000 rpms and don't touch it anymore. With that I get close to 23 mpg on petrol.

Find the rpm where your V8 is in "cadence" . Mine is 2700rpm/70mph in 5th gear. Slower than that it will struggle to climb a hill in 5th and then I am buggered by having to put my foot down without any acceleration.

That's when my fuel economy is rapidly going down.

FlyingDutchman said:

Is it for FUEL economy, or general economy.


And when you need serious power ( that's why it is a V8 and I have one for the experience as well ) you need petrol anyway.

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Thanks for useful posts.

I think this one is the clincher really, If I v8 I would not want to compromise on performance, so gas looks like it is out of the window, which leaves the petrol only v8 left. I'm sure there are some economy improvements to be found with a bit of time and effort but probably not enough for what I am looking for. (not that I was ever expecting good economy!)

gas doesn't compromise if set right

Dr_evil said:

gas doesn't compromise if set right

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Agree totally!

When we tow our big trailer at 3500kg loaded:



- we need every pony we can get, and it does the job very well. There is no noticeable difference between petrol and gas, only in the morning before it is all warmed up, if fluffs a bit at the changeover, but fine immediately afterwards.

Peter