MPG on LPG?

[AngeloEvs]

The GO-LPG website explains why LPG fuel consumption is higher:-

LPG is slightly less potent as an internal combustion engine fuel. The driver will instinctively react to this by opening the throttle more to achieve the desired speed or rate of speed increase (often called acceleration). Thus, more liquid fuel (LPG) will be used than when running on petrol.

In a nutshell, to achieve economy don't drive as fast and don't accelerate as hard if economy is your goal. A 1.9DG is effectively a 1.9DF on LPG and T25's have the aerodynamics of 1500kg brick.

As for cold starting on LPG. Here is the GO-LPG advice but opinion is divided on this issue, I run my Sierra purely on LPG and have done so for the past 7 years:-

http://www.go-lpg.co.uk/Do_I.html

[toomanytoys]

The first thing you do oncew converted to LPG is to advacne the ignition timing., that claws back most power and mpg loss.. Yes the calorific value is slightly lessso therefore you need more fuel, but its knock resistance is so much more..

my 78 bhp DG didnt turn into a 60bhp slug once lpg fitted and once set up properly, you would be hard pressed to tell the difference..
I used to get about 2mpg worse on LPG.. and now it has the DJ spec engine in, it goes better and does the same mpg as the DG did on petrol..

Currently biulding a couple of engines, one to take better advantage of the high octane of LPG...

Its a bit like the E85 problem manufacturers had.. the engine needs to be modified/setup for E85 properly or its a waste of time..

[AngeloEvs]

At least we have someone else who is getting similar MPG on LPG as they did on petrol, different approach but same outcome which some are very sceptical of to say the least. My mistake, thought the DF was 68 HP, its around 10-12% power loss on LPG (I stand corrected!

[steve8090]

If most LPG systems are set correctly and the engines tuned properly the LPG system will match or even in some of the bigger engines like the 4.0ltr Discovery better petrol consumption by a considerable amount.
Both of my vehicles, a 2.0ltr Aircooled and a 2.0ltr T4 match the petrol consumption easily.
Please be aware thar LPG will highlight any problems in the ignition circuit and multiply the problem, timing the engine properly is important and if you use the open loop system constant adjustment to get the optimum is also important, a gas analyser is almost essential to set and verify the correct running, your local freindly (tongue in cheek) MOT station should let you use their analyser if you ask nicely, rember to keep an eye on the 02 reading, too much means a manifold or carb leak, ideal settigs for the LPG on the VW motors is C0 should be set to 1.5 - 2.0%, c02 reading (not adjustable) should be in the region of 11%, HC (a measure of unburnt fuel in the exhaust) should be around 600ppm, less is better more tends to lean towards a tired motor or other leakage problems look at the 02) up to 1200ppm will pas an MOT, ideally if you can spend the time you need to get the Lambda reading to 1 (or as close to 1 as you can) this is a culmination of the other readings and will give optimum performance for your engine conditions.

[David Last]

Hi all, I have been reading this thread with great interest as I am seriously considering an LPG conversion.
I have a 1990 Autohomes Komet HiTop with a 1900 cc petrol engine and with sympathetic driving get between 26, local, and 34mpg, steady motorway cruising(56mph). I see references to the "DG and DF" engines but don't know which one refers to mine. I would be very happy with a couple of mpg reduction under present fuel costs.
Conversion costs would seem to vary quite a bit but I guess there is an element of "you gets what you pay for" in it.
Any comments welcome.

A great Forum
Cheers
David Last
Cornwall

[Mocki]

both the DG and the Df are 1.9 wbx engines, you need to look on your engine number to see which you have, but its a fair bet with the age your van is its a DG.

I get the same mpg from my 2.1 ( on a carb) on petrol and on LPG, as far as i can tell........... but ive done 16k miles on lpg since last mot, and only 55 miles on petrol, so accuracy is questionable on those figures.
One thing is for sure, im not getting anywhere near the 34 mpg you are quoteing, best is 26 last month going down to cornwall when i burnt a whole 55 litres of gas without stopping, infact other than starting off and stopping at the next fuel fill, it was all at 60-70mph.

[joshb]

34mpg... what am i doin wrong.....

[synaptyx]

I'm just about to fit a new fuel gauge to the van, it looks like this:

[IMG100]http://i26.photobucket.com/albums/c108/ ... lguage.png[/img]

[David Last]

I'll come clean JOSHB, Brim full tank at Keswick on a Sunday 6am down the M6/M5 at a constant 50/56 mph, 1 pee stop, then a fill to the brim at Sedgemoor on the M5. I did the sums and it came out at 34.4mpg.
I passed TWO vehicles, a horse-box and a flat cap out for a Sunday drive!.Otherwise the whole world pased me by and I had a totaly stress free trip. Having done this trip before under similar circumstances and trying to keep up 65-70 average I got about 26 mpg and a lot more hassle!
Dave

[kevtherev]

can I see your sums David?.. I like to mark it

[AngeloEvs]

I quoted 27+ on petrol at a steady indicated 56mph, however, my satnav indicates around 50 mph, so I'm a slow b******r for sure and with a 10% error I'm probably clocking more miles than I am actually doing.....bum!

[Mocki]

your definately clocking more miles than your doing....... 28 more every 200...... which is 14% by my reconing........

[joshb]

so 27mpg with a 14% error is actually 23.33mpg... i think... I would humbly suggest that the 34mpg may be subject to an error factor..

[AngeloEvs]

Hadn't noticed it before but I reckon the speedo error is down to the Carat alloys. Have to put standard 185's on, got a new set on the old steels.

[lloyd]

speedo and odometer may not be off by same %.