Audi A8 This full sized Audi A8 sedan offers interior luxury and spaciousness comparable to any car in the full sized luxury sedan class

lpg

  #1  
Old 04-04-2006, 12:13 PM
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Join Date: Apr 2006
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Default lpg

I wonder if anyone knows if LPG systems are a good idea on the 4.2 A8s and if so which system?

Thanks Rupe
 
  #2  
Old 04-04-2006, 08:51 PM
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Default RE: lpg

Do you mean Liquid Propane??

If so, WTF would you put that in a gasoline engine for????
 
  #3  
Old 04-04-2006, 09:56 PM
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Default RE: lpg

LPG is an abbreviation for 'Liquefied Petroleum Gas'.
There are two basic types of LPG, Butane and Propane. Propane burns the hottest.

In Europe LPG is commonly sold in garages and is about 45% the cost of petrol. The fuel does not burn quite as efficiently, but the net result is that you can still half your fuel bill. Petrol here is about $8 a gallon.

LPG is considerably better for the environment. In my case, in an average year the car will emit 2 tons less carbon dioxide. Thus the government in the UK promotes it. As an example driving through central London there is a $14 daily charge $2,800 a year for many people. If a car is converted to LPG and passes certain tests you are exempt the charge.

There seems to be a number of different systems that can be used, but none are approved by Audi - basically they have not done the testing and why should they. Looking at other cars some seem to experience the exhaust valves being burned out. It is possible to detune to get around the problem (I believe). The real problem I have seems to be that the best source of info seems to be from the garages selling the systems and as such they are not impartial.
 
  #4  
Old 04-05-2006, 05:34 AM
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Default RE: lpg

I've had quite a bit of experience with LPG - not in my Audi though. I used to own a '74 Toyota Landcruiser which I had properly worked up for 4x4 trials/rallying. I put a chev 350 V8 (6.2l) into it, and ran it from LPG.

LPG being not quite as good buring as gasoline is a myth - it actually has a higher octane rating and hence can output more power than normal gasoline. If you look at a lot of racing stock cars, they run on LPG and run faster and more powerful.

Sounds great, but there is a lot of work to get your car running PROPERLY on LPG.

The normal car kits you buy basically mean you put an LPG tank into the car, and have it hooked up to pump LPG into your carbs just the same as petrol. So you can run both LPG and Petrol at the same time. The thoughts in the past have been that petrol is universal, and you can get it anywhere, so if you run out of LPG you can still use petrol and you car will still get from A-B.

With the prolification of LPG now, and you get a decent map book of your country/city highlighting all LPG refueling points, you might be confident enough to switch fully to LPG.

To do so, a lot of work needs to be done:

Tanks: Because normal gas tanks are not presurised to any sort of degree, they can be any shap hence car makers can basically slap them anywhere in the chassis. Hence going to LPG, even if you're not going to use your petrol tank again, there's no point in removing it. You have to have an LPG rated mechanic close it off, literally vacuming out petrol fumes. A 1/4 or almost empty tank of petrol is a lot more likly to be a potential car bomb rather than a full tank.
THEN you have to get an LPG cylinder installed - fine for an A* - it's got loads of trunk/boot room, and will still have enough room for a lot of suitcases etc. once you have a LPG cylinder mounted in the back. However, for a V8, those hungry things, you will need AT LEAST an 80-100litre cylinder - I have a 60 litre tank (all I could fit) in the 'cruiser, and with the 6.2l V8 I was getting roughly 80-100km per LPG fillup. I did drive it like a maniac though - heavy foot etc. ;-) There are websites that will help you calculate your fuel efficiency using LPG based upon engine size, car weight/type etc.

Carburettor: This is made for petrol, so say goodbye to that! The Chev 350 I had is such a common engine that it was easy to find a carb made for LPG that bolted straight onto the manifold. I can't say about the Audi....
It's not critical - you can still use the petrol carb, but it will reduce your power output, and have a shorter life as the molecular structure of LPG very different than petrol, hence damages it in the long term. It's basically all about the air mixture - how much air to LPG ratio etc.

Engine Cylinders: These need to be hardened or replaced - replaced is better - suited to LPG.

Possible use of third party engine lubrication injection system: you see this more commonly with CNG (Compressed Natural Gas) conversions for an engine, or with older car engines that were made for 96 leaded petrol now running on 96 or 91 unleaded. The lead basically adds a lubrication agent to the engine, and without it, you need this lubrication inject. It's a unit they bolt under your bonnet, about the size of a large fist, injecting into the carb - you need to refill it every couple of months with a lubrication liquid - not expensive, but a bit of an annoyance - one more thing to think about. The Audi V8 is made for unleaded, but LPG has considerable less lubrication qualities than petrol.

Engine timing: The biggie! This is what makes the most difference. Petrol and LPG work on the same principal - suck squeeze bang blow - four stroke engine. Due to the different octane rating, the engine cylinders need to be in a different position to obtain full compression of LPG and O2 mixture than using petrol. This is the reason that most people think that LPG is less powerful than petrol - they're putting lpg through a petrol engine, using the same timing for petrol. The mixture of LPG and O2 in the engine is not properly compressed at the time the spark goes off in a petrol engine, hence you're really burning only somewhere 70-80% of the LPG efficiently - the rest going out the exaust. So a poorly timed LPG engine is actually guzzling more gas, for less power, and emitting more emissions than a petrol engine. Lucky thing that LPG is more "green" for the environment than petrol.

There are numerous other little bits and pieces to look at, but those arethe major ones.

Recap - Engine change over from fully Petrol to FULLY LPG:
Tank
Carbs
Engine Cylinders
Lubricant injection
Engine Timing

Lastly - the Audi engine is NOT over-engineered like a chev 350 engine - ie. the chev is a big block mother than can take a hell of a kicking. A typical chev 350 will easily go 250,000 miles - 300,000 miles with minimum maintainence and still keep on ticking - running LPG through it gave it an estimated 3/4 shelf life. Fine for me - I wanted the performance. I ended up with a complete fibreglass body making a very light V8 Toyota Landcruiser - and - I know you'll find it hard to believe - 540bhp to the wheels!!! I could spin all four 12.5" 36" diameter tires on concrete - it was literally a real beast. (Oh - I did have other toys on it to get that power, - hardended racing crank, speciality manifolds, and a dirty great super charger bolted to the top of it.)
You will be shortening the lifespan of your Audi V8 engine going to full LPG - even properly done. You can have it done properly so that it is as reliable or more than a petrol engine however.

My advice - if you want a cheaper running car, buy a honda civic. But if you seriously drop the money and get professionals to do the proper work (my complete engine rebuild, and installing of LPG was approx. 30k NZD) you can look forward to more power, cheaper running, reliable car that kicks ***!

PS. If you go down the road of the half and half - half petrol, half LPG, someone told me a few months ago that there are better kits available now that a one stop shop can put in which with the flick of a switch helps advance the engine timing etc.
Definately let your fingers do the walking - find a few garages that really specialise in LPG, and start talking.
 
  #5  
Old 04-05-2006, 06:03 AM
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Default RE: lpg

Sorry - just re-read your post.

Valves are also included in the replacements needed along with the engine cylinders - basically need to be hardened. They typically burn out becuase the LPG mixture is either incorrect from the carb or the timing on the engine is inefficient.

As I mentioned firstly in the post, stock car racers etc. typically use LPG. Try a few high performance garage specialists who are not the typical "kitset LPG" people if you want the lowdown on LPG engines. As they typically strip and rebuild the engines regularly, they can tell you the pros and cons. They will most likely snob the kitsets as they are not "proper", and give you a great "devils advocate" point of view.

I lived in London for about 4 years, but have no clue where to find these people myself - sorry! Try finding british racing clubs online, that talk about LPG, and drop a few people a line. They will give you some great contacts with the specialist garages.

I've found this - no doubt you have too - and it really touches nicely on the alumuminum problems, but nothing about engine bits.
http://www.go-lpg.co.uk/Audi_A8.html

This site to me gives you the best information - I must admit I went off a bit about full LPG conversion in my previous post - this site I think will be the best guide for what you actually need to do, and common FAQ's very helpful.
http://www.rpiv8.com/faq-lpg-gen-info.htm

Please let us know your decision - I'd be very interested to know how it works out.
 
  #6  
Old 04-05-2006, 06:11 AM
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Join Date: Mar 2006
Posts: 8
Default RE: lpg

And completely last post ;-)
Don't know which year your A8 is, but I assume that the newer A8's still use the same cam belt timing system. These should be replaced regularly (or at least checked up on). It's sort of major work - I just got my '98 A8 completely serviced - new cam belt, water pump etc.

Having the engine open at this level would be a good time to consider dropping in an LPG kit.
 
  #7  
Old 04-06-2006, 08:10 AM
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Join Date: Apr 2006
Posts: 3
Default RE: lpg

Thanks very much for such a full account of the issues. I am familiar with go-lpg and the garage seems to have a good reputation.
 
  #8  
Old 06-02-2006, 07:51 PM
Join Date: Jun 2006
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Default RE: lpg

LPG sucks! If you wanna to drivin for small money buy Toyota or Smart. LPG in A8 4.2 isn't a good idea this car has incredible power and it's bad to waste it. I think it's mayhem of this car.
 
  #9  
Old 06-15-2006, 12:04 PM
Join Date: Jun 2006
Posts: 2
Default RE: lpg

Hi, I have just bought a 2.8 A8 runnig on LPG. Bought on Ebay for £3000 with 85000 miles on the clock. Not had a cambelt change yet so that is my first job along with a good service. I pick it up next week so will let you know how I find it to live with. Doing 100 miles a day made LPG a necessity as I am not going to sit in traffic in a Micra/Corsa for the sake of fuel economy when I can sit in an Audi for Micra/Corsa money!!

Regards

Phill
 
  #10  
Old 06-28-2006, 12:07 PM
Join Date: Jun 2006
Posts: 2
Default LPG 2.8 A8

Well,

I have now picked up the A8 and it is runnig fine on LPG. I had to re-position the filler cap as it was below the back bumper and was a nightmare to fillup. The car starts on petrol and automatically switches to LPG. The switch is seemless and you cannot even notice. I do however notice that I can get LPG for 42p per litre from a non franchise gagare (the garage that altered the location of the filler cap in Andover). I cannot believe that I got it so cheap given the mileage but a new cam-belt is going to be approx £400 and a service probably £200. So all in for around £3500 I have a spanking motor. Well pleased.
 

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