Thread: 3.9 V8 Fuel economy!?

Thanks all!

Well i am surprised that 20l/100 is the norm but if that's the case ill just need to make damn sure i keep the foot in check and maybe look into gas conversions.

Maybe take the train a bit more as well!

Yep, i am using about 20l/100km too. That is in 90 with 3" lift and 35" tyres with a very rich tune (you can smell the unburnt fuel). I thought mine was particularly high but by the sounds of things isnt so bad.
Combined with the 45l tank I only get about 200km before the light comes on!

I have a BMW 123d coupe as my economical car, averages about 5/100km if i can resist putting my foot down! More power and more torque than my 3.9 V8 too, things have certainly moved on since the 50s!

Well i am surprised that 20l/100 is the norm but if that's the case ill just need to make damn sure i keep the foot in check and maybe look into gas conversions.

Maybe take the train a bit more as well!

I have tried just about everything economically possible to improve economy on my 92 RRC including Oxygen sensors, Thor manifold, Unichip with far more "vacuum" advance , free flow exhaust, modified heads, new cam etc etc.
I still get about 20L per 100kms around town, admittedly in a very hilly area where the main trip is over a Mountain( well big hill at about 300Metres)
On the highway I now think I have improved about 5-10%

IMHO one of the issues is that the auto does not lock up until 80Kmh so you are slipping the torque converter all the time, although I note the offical figures for a manual are almost as bad. I think some of the better performace of the D2-38A is from the electronic lock up transmission.

I do not agree that other large petrol 4WDs are better. When you read forums and see what a Jeep Grand Cherokee, Landcruiser, Patrol, Jackeroo, ChallengerV6, etc get it is not all that better.

I had one of the first Jackeroos with a little 2 litr engine and it only did 15 L per 100 on the highway , as did my second 2.6 Jackeroo. My GQ Patrol was worse at about 17L per 100 on the highway.

The reality is you are moving over 2 tonnes with the aerodynamics of a brick outhouse.

BUt really have a look at the economics of changing the car. By the time you spend a lot of money to get a modern diesel , stamp duty, insurance etc ,IMHO it is impossible to justify . In my case on a 20KK trip I am out pocket say $1500 petrol (@17per 100 pulling my camper trailer=$5100)vs diesel ( @12l per100 pulling camper trailer @ 1.50 =$3600).

However in my case I would outlay say 30KK on a decent late model diesel , and that would not get you a D3 with low Ks say at 5% opportunity cost $1500, depreciation at say 10%= $3000, insurance at say $1000, servicing if under warranty blah blah.

So really , if you have an old but good D1 or RRC , the extra petrol pales into insignificance over selling and buying a more modern economical diesel.
Regards Philip A

Well , Ive seen consistant 25 to 26 MPG (10.8 / 100 to 11.3 /100) out of 3.9 RRC at 110 KPH . Only one problem,not much change out $10,000 to do it. Again ,the issue with Rover V8's is their pathetic Volumetric efficency.So with the right headwork ,11.5 static comp,correct rocker geometry and clearances.the right cam,dialled in (anyone who uses the dots method simply hasnt got a clue how an engine works!).Then a half decent EFI system such as Haltec/motec/megasquirt etc with sensible ignition and fuel maps . Is it worth the effort/cost ? might take 3-5 years for payback ?

I had a '96 3.9 auto and it's still my favourate,I fitted gas to mine and never looked back,don't buy the cheap system,go the sequental injection and it'll give more performance with better ecconomy.I would loose some boot space and fit the 120ltre tank behind the back seat,that will give you near 800k's range with petrol still to go.The vac advance not working is a very common problem with them also,a straight swap out for a reco one is an easy fix. Pat

I couldn't agree with you more Philip regarding the economics of changing vehicle to save money on fuel.

I did that calculation last year, for my soft dash classic, when I bought a caravan and concluded that for the Kms I did it it made no economic sense what so ever to change to a diesel.

Pity an electrical fire wrote him off recently so I am back in the market anyway.

Cheers

Steve

Originally Posted by 400HPONGAS

Well , Ive seen consistant 25 to 26 MPG (10.8 / 100 to 11.3 /100) out of 3.9 RRC at 110 KPH . Only one problem,not much change out $10,000 to do it. Again ,the issue with Rover V8's is their pathetic Volumetric efficency.So with the right headwork ,11.5 static comp,correct rocker geometry and clearances.the right cam,dialled in (anyone who uses the dots method simply hasnt got a clue how an engine works!).Then a half decent EFI system such as Haltec/motec/megasquirt etc with sensible ignition and fuel maps . Is it worth the effort/cost ? might take 3-5 years for payback ?

But if you're building a new engine anyway, then it's not so bad.

And the other thing is the gearing.

In Old Money, my '67 2.3 litre 3spd/ o-d Crown did 26 mpg overall Perth-Adelaide-Sydney - Brisbane-Sydney-Melbourne -Adelaide return, before the Nullabor was sealed. This included most of the gravel at insane speeds (had to drag off my mates XY Falcon, who managed 24 mpg all up) I'd get around 24mpg around town.
Falcon was about 100kg heavier than the Crown, but I was 100kg heavier than said mate....

The HZ Holden 253" V-8 did around 14 to 18mpg, usually 16 to 17mpg. Did'nt make much differance metro or country spee...er running.
Fuel was around 19 cents per litre...

CM Valiant on 245" / 4.0 litres was around the same, usually 17 to 20mpg. Properly set up they could do up to 28 mpg on long gentle 100km/h runs

Current Holden V-8s apparantly can match this with gentle driving etc.

"Economy" should never be used in the same sentence as standard landRover 3.9litre v8.

I like "20 litres per hundred km, " as its got a "20" in it, reminds me of "20mpg" .... 14mpg is just too depressing.... as bad as the Jackeroo I WAS looking at. Prado and Nissan owners are happier with fuel costs.

LPG, done properly, seems to be the only way out of bankruptcy.

From past experience, the boot on a RRC is so tiny, made worse by the drop-down tailgate which pushes you further away from reaching IN, - or climb UP onto it to reach beyond 18"... you may as well fill up the dead space with LPG tank(s) !