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Old 03-23-2012, 06:50 PM   #1 (permalink)
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LPG driving for Economy?

My current Car share Colleague is off to pastures new in April, So I'm landed with having to drive myself to work every day now..

To this end, for the benefit of my wallet, I have acquired a 1997 BMW 328i touring (estate) fitted with a single point LPG coversion. Car has a 5 speed Manual transmission

This has the benefit of giving me fuel at circa 0.83/Litre as opposed to 1.35/Litre for petrol.

I know I wont have the full 193 ponies available on LPG, but as its my commuting car, that doesnt matter.

I'm more interested in making it as cheap and efficient to run as possible
My route is 25 miles each way,

approx 22 miles motorway (rush our, so plenty low speed/accellerate/slow down) scenarios

3 milees town driving- fairly free flowing


At the moment, my iS returns circa 40mpg on this run- I'd like to get as close as possible- I realise I have a larger engine and LPG is inherrently worse for MPG due to lower energy content, but I do have High gearing (in relation to the iS) and more torque


Initial thoughts are similar to the iS

42psi in the tyres

P&G where possible (will it work with LG?!)



I'm open to all tips and suggestions

thanks

Neil

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Old 03-24-2012, 05:02 AM   #2 (permalink)
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is it dedicated LPG only
is it duel fuel, pump gas and LPG
or is it a converted gas auto


dedicated engines commonly have a little higher compression, then one that must also run on gas.
LPG just like ethanol, has lower BTUs and has a high octane rating, and very much likes high compression.

but when the engine was made orignaly to run on gas, but is converted to LPG, the economy will suffer a bit do to having 9 to 1 or so comp.

buy no means is this your cars mpg numbers, but it gives a "ball park" as to what is lost in MPG from gas to LPG
i wanted to show a car but i could not find a USA car that is LPG/gas powered off the dealer lot.... there's a few CNG cars, but not LPG cars.
Compare Old and New MPG Estimates
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Old 03-25-2012, 12:30 AM   #3 (permalink)
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Neil,
My car is converted to run on LPG as well as the factory fitting of unleaded petrol and the general level of economy is around 10 / 15% less with gas than petrol.

The gas does vary in quality and mix and here it is possible to buy either LPG (Propane and Butane mix) or just straight Propane with no butane.

The propane and butane mix will give better economy but the 100% propane gives better starting and performance with lightly less economy.

P&G will work with lpg. I don't do it but a taxi driver I know does.

Apart from the lower costs at the forecourt there is no practical difference running on LPG and all the usual tips and tricks apply as they do to a standard petrol powered car.

The oil will last longer since there are fewer combustion byproduct deposits but LPG is more demanding on the ignition system than unleaded so good quality plugs and leads are a must.
I use NGK plugs and change the leads every 100 000 klms (about 60 000 miles) just as a precaution.

Peter.
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Old 03-25-2012, 10:20 AM   #4 (permalink)
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Colder plugs are a must, and you should make sure your particular engine doesn't have valve seats that are sensitive to LPG.

I love LPG, but at the moment, my LPG-powered car is idle. Don't have time to work on it, so I commute with the diesel instead, or whatever test unit I've got at the moment.
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Old 03-26-2012, 04:12 PM   #5 (permalink)
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The Mistress - '88 Bmw 320i Touring SE
Team m8
Last 3: 27.17 mpg (US)

Germany Beadle - '91 Mercedes 300td (estate, N/A)
90 day: 24.63 mpg (US)

The Bloodylingo - '05 Citroen Berlingo Multispace Desire
90 day: 39.77 mpg (US)

Shanner Scaab - '03 Saab 9-5 estate Vector
90 day: 26.19 mpg (US)
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Quote:
Originally Posted by Peter7307 View Post
Neil,
My car is converted to run on LPG as well as the factory fitting of unleaded petrol and the general level of economy is around 10 / 15% less with gas than petrol.

The gas does vary in quality and mix and here it is possible to buy either LPG (Propane and Butane mix) or just straight Propane with no butane.

The propane and butane mix will give better economy but the 100% propane gives better starting and performance with lightly less economy.

P&G will work with lpg. I don't do it but a taxi driver I know does.

Apart from the lower costs at the forecourt there is no practical difference running on LPG and all the usual tips and tricks apply as they do to a standard petrol powered car.

The oil will last longer since there are fewer combustion byproduct deposits but LPG is more demanding on the ignition system than unleaded so good quality plugs and leads are a must.
I use NGK plugs and change the leads every 100 000 klms (about 60 000 miles) just as a precaution.

Peter.
Thanks for all the info- time to check the car out and see what I have to work with

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US MPG for my Saab 9-5 2.0t Estate


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