60mpg in a S500

Borys

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So after thinking about it for a while finally I've got a lpg system installed.
Result normal run 30mpg but as gas is half the price we got 60mpg.
For 50£ in a town will do 250 miles.
Was thinking about a diesel car but it would be a mistake I recon.I'm left now with a great comfort,performance is the same and that v8 sound is still with me.
In 3 months the installation will be back in my pocket.
Really happy now can enjoy my w140 for a bit longer now :rock:
 
D

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LPG burns quicker than petrol, so you don't quite get double mpg, but either way it's still a big saving.
 
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Borys

Borys

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It use to burn quicker.Now with the injection systems you wouldn't tell a difference.
 

tromppost

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by these I could have got 34mpg !!

on avg I get 18mpg.
 

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DSM10000

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It use to burn quicker.Now with the injection systems you wouldn't tell a difference.

LPG has a lower energy density than petrol (i.e. there is less energy available per unit volume) so although it has a higher octane rating and burns more cleanly it will have a slightly higher specific fuel consumption than petrol but the large cost differential still makes it a much cheaper fuel to use compared to petrol.
 

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DSM10000 said:
LPG has a lower energy density than petrol (i.e. there is less energy available per unit volume) so although it has a higher octane rating and burns more cleanly it will have a slightly higher specific fuel consumption than petrol but the large cost differential still makes it a much cheaper fuel to use compared to petrol.

Exactly its only because its cheaper that it works out more cost effective. The s500 did the cost equivalent of 60 mpg of petrol at its current price. In reality the car did no where near 60 mpg
 

flango

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With the new Gen4 LPG systems as a rule of thumb you get approx double the mileage for your money. So if your car did 30 mpg on Petrol it will do 30 mpg on LPG, but because LPG is roughly half the price of Petrol you get 60 mpg equivalent. The latest Gen4 systems come with very sophisticated ECU's and injectors to enable the LPG to be burned as efficiently as possible. With the old systems you used to get between 80% - 90% of the petrol consumption now you get like for like so LPG is a real good alternative to a diesel motor at the moment, particularly at 69p per litre :)

we have just installed a Gen4 system on our Discovery V8 and you can't tell when it's on LPG and when it's on petrol and it's now giving 38 mpg - 42 mpg equivalent depending upon what it's doing as it's duty.
 
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Borys

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With the new Gen4 LPG systems as a rule of thumb you get approx double the mileage for your money. So if your car did 30 mpg on Petrol it will do 30 mpg on LPG, but because LPG is roughly half the price of Petrol you get 60 mpg equivalent. The latest Gen4 systems come with very sophisticated ECU's and injectors to enable the LPG to be burned as efficiently as possible. With the old systems you used to get between 80% - 90% of the petrol consumption now you get like for like so LPG is a real good alternative to a diesel motor at the moment, particularly at 69p per litre :)

we have just installed a Gen4 system on our Discovery V8 and you can't tell when it's on LPG and when it's on petrol and it's now giving 38 mpg - 42 mpg equivalent depending upon what it's doing as it's duty.

Thank you for your supportive post :)
 

DSM10000

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Thank you for your supportive post :)

No one is doubting that LPG is more cost effective for many applications than petrol but you cannot change the laws of chemistry and physics. LPG has less energy available per unit volume than petrol.

Undoubtedly there are ways to make the LPG burn more efficiently but you can never get around the above.

LPG has a typical specific calorific value of 46.1 MJ/kg compared with around 43.5 MJ/kg for premium grade petrol .However, its energy density per volume unit of 26 MJ/l is quite a lot lower than that of petrol.

With LPG at the current price it is the cost per mile that is in it's favour. You do not get 60mpg, the car will use far more than a "gallon" of LPG in terms of volume to cover those 60 miles.
 
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flango

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No one is doubting that LPG is more cost effective for many applications than petrol but you cannot change the laws of chemistry and physics. LPG has less energy available per unit volume than petrol.

Undoubtedly there are ways to make the LPG burn more efficiently but you can never get around the above.

LPG has a typical specific calorific value of 46.1 MJ/kg compared with around 43.5 MJ/kg for premium grade petrol .However, its energy density per volume unit of 26 MJ/l is quite a lot lower than that of petrol.

With LPG at the current price it is the cost per mile that is in it's favour. You do not get 60mpg, the car will use far more than a "gallon" of LPG in terms of volume to cover those 60 miles.

Note where the OP is from :thumb: no one is doubting the chemistry or physics you are bang on it just needs qualifying that it is 60 mpg "equivalent" in petrol terms. The real mpg for the LPG will be around half that.
 

DSM10000

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Note where the OP is from :thumb: no one is doubting the chemistry or physics you are bang on it just needs qualifying that it is 60 mpg "equivalent" in petrol terms. The real mpg for the LPG will be around half that.

Absolutely!!

Had not noticed the OP was fvrom Moscow!:thumb:
 

Usuf_x

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To add I have LPG fitted and you cannot tell the different in the car running, though the savings are great and I have already paid off my installation cost.

My car averages 22mpg on LPG and 25mpg on Petrol.

Therefore 44MPG to the equivalent cost of running on Petrol
i think i got it right
 

DSM10000

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Whats really good on the GEN4 systems is you can co-fuel so you can run on LPG and Petrol at the same time, now there's more bang for your buck :D

Why would you want to run on both at the same time? I thought most if not all LPG systems started on petrol and switched to LPG after a brief warm up period?

There is a limit to how much fuel you can burn and it depends on how much air (well Oxygen to be accurate) you can get into the cylinders as well as how much exhaust you can scavenge at each cycle.

Never heard of dual fuel cars running on both, sounds interesting, dol you have any details?:)
 

DSM10000

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To add I have LPG fitted and you cannot tell the different in the car running, though the savings are great and I have already paid off my installation cost.

My car averages 22mpg on LPG and 25mpg on Petrol.

Therefore 44MPG to the equivalent cost of running on Petrol
i think i got it right

At about half the price of petrol but burning a little more per mile LPG is not quite half as cheap per mile.

It is a little confusing to talk about mpg as LPG is burned at a higer rate per mile, the cost per mile is where you are potentially saving money.
 

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A lot of assumptions being made I think :dk: Some of which are assuming that when running on LPG the timing, fuelling and mapping of the engine is the same as when running on petrol. This is not true of the latest systems they run their own ECU and adjust the engine parameters to efficiently burn LPG, the fuel maps for LPG are significantly different to petrol as is the timing. For example at low rpm LPG burns slower and more advance is needed at higher rpm it burns faster so when compared to petrol does not need as much advance.

The new systems are light years ahead of what people think of when they think of an LPG car
 

DSM10000

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A lot of assumptions being made I think :dk: Some of which are assuming that when running on LPG the timing, fuelling and mapping of the engine is the same as when running on petrol. This is not true of the latest systems they run their own ECU and adjust the engine parameters to efficiently burn LPG, the fuel maps for LPG are significantly different to petrol as is the timing. For example at low rpm LPG burns slower and more advance is needed at higher rpm it burns faster so when compared to petrol does not need as much advance.

The new systems are light years ahead of what people think of when they think of an LPG car

I was not making such assumptions, perhaps you were making some assumptions of my and others knowledge on this? It is not about scoring points jbut about clarity.

I am aware of the newer systems having seperate ECU's etc as I have looked in to this in some detail. I just chose not to include that information in my replies as the point I wanted to make was in reference to the specific chemistry and physics of LPG vs petrol and to dispell the myth that LPG cars travel further per gallon / litre etc when clearly they cannot when in fact what LPG gives is a lower cost per mile and a cleaner burn with a lower pollution burden.

This difference in fuel burnt per mile is perhaps shown more clearly when an average LPG tank of 80 litres would give you a lower range in miles etc than an equivalent size of petrol tank plus all LPG tanks have a capacity that is approximately 20% lower than maximum due to space required for expansion.

It is clear that the adoption of specific mapping etc will make LPG cars more reliable, drivable and fuel efficient and yes it is much cheaper per mile in terms of cost of fuel burned
 

MarkP80

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So after thinking about it for a while finally I've got a lpg system installed.
Result normal run 30mpg but as gas is half the price we got 60mpg.
For 50£ in a town will do 250 miles.
Was thinking about a diesel car but it would be a mistake I recon.I'm left now with a great comfort,performance is the same and that v8 sound is still with me.
In 3 months the installation will be back in my pocket.
Really happy now can enjoy my w140 for a bit longer now
- That's what I call a result Borys, nice one!

MarkP
 

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