When towing my caravan behind my 93 3.9 single point mixer lpg system with twin 36l underslung tanks I get 180 / 195 miles full to empty. I live in North wales and tow anywhere from the Peak district to the west Wales coast (so prety varied terrain) MPG doesn't bother me so much as distance per fill but i'm getting about 2.5 miles per litre @ 45p per litre I recon that's OK.
When towing the same caravan behind my 2001 4.0l P38 with injection lpg and 95l tank I get 240 / 260 miles full to empty.
 
My 52 plate 3.9 V8 lpg gives me 180 to 200 miles on 60 litres gas. Not towing though. From what I can see your numbers look about right
 
To supplement our twin torpedo tanks (48 litres net) we have bought a 110 litre tank to go behind the rear seats. This gives 88 litres net, so 136 litres at 3 to 4 miles per litre on motorways, more on the back roads. Plus the full petrol range as well, so we could do Scotland and back on both petrol and gas.

The intention is to make a QD frame assy and have self-sealing quick-release connectors for the gas pipes, so it can be taken out fairly quickly. The floor will have threaded inserts set in steel bar which in turn is bolted to the floor panel.

There are regulations about installation, and nominally there must be no gas release inside the car in use, but the self-sealing connector that we found seals BOTH halves of the coupling when pulled apart, so that's sorted out.

The other pipes are to be dealt with, there's no need for a gauge as it will run into the pipework between the other tanks, so just a filler pipe and an outlet pipe to worry about.

There is also a safety vent fitted on all tanks, I need to work out if that needs to be taken outside the body or not. Can anyone with a RR or Disco with rear internal tanks advise what they have fitted, please?

The QD gas connectors are about £22 a set plus VAT and postage. I'll advise which one I use later on, and will do some pictures to show how it all went together. Last job will be getting is certified for the insurance.

Peter
 
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If you're returning 3 to 4 miles per litre, you're very close to burning your valves out even if you're using flashlube. All connectoins and valve boxes MUST be vented to outside to comply with LPG code 11 (not legislation but recognised and refered to by insurance industry in claims events)
 
SuperPete said:
If you're returning 3 to 4 miles per litre, you're very close to burning your valves out even if you're using flashlube.
Click to expand...

Could you expand upon that? It doesn't seem to be particularly different to what others are achieving, and the valves weren't bad when we had the heads out for the engine rebuild.

Peter
 
An update:

On a cross-country run and a bit of the M25 and A10 (Rushden to Waltham Abbey) we got 15.30 mpg on gas.

Peter
 
Hisuperpete
I'd like some clarification on the valve issue too as I regularly get 17mpg on a run and 14/15 normally.
D2 v8 4.0 multipoint injection lpg
 
Picked my first V8 up last night:D Started off with full tanks, did 153 miles at mostly at around 60 on cruise control, tanks only took 35 litres I make that nearly 20mpg. Well pleased not sure I'll manage that all the time though!!
 
You wait til you start to enjoy the sound of a V8 and start pressing the loud pedal a bit more - then you'll see a difference :D
 
I bought a USB interface kit and software to have a peek at the gas ECU. Bought yesterday and arrived this morning, very quick service.

Not much for your money, but as long as it does the job....

I'll have a play tonight and see what I can twiddle :D

Peter
 
I get a regular 250 miles near enough on the nose regardless of how I drive mine, and it's an auto, I can get around 100 litres in before it cuts the fueling off. So basically, 250 miles for £45-50, not too bad, but I did expect better when I bought it.

G
 
BoomerV8 said:
You wait til you start to enjoy the sound of a V8 and start pressing the loud pedal a bit more - then you'll see a difference :D
Click to expand...

I did, on a cross country run from the M5 up though Mid Wales to home, all I can say is woo hoooooooooooooo:D:D:D
 
hiya,
I have a 3.9 RRC auto. used to get around 164 to a fill. running 2 underslung 36l tanks. Now from what I have read, I should get about 56 litres at the pump. Very rarely run the tanks empty though so not sure on that.
The scary thing is I filled up at a BP in Bedford once and got 71 litres in. And the tanks were not empty.
 
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