Stewart Hargrave said:
In a properly set up installation you will lose a few % in power, but
12 - 15% may be overstating it some.
Okay, I'll now step in and disagree with both of you.
I spent my apprenticeship as a mechanic installing LPG on vehicles.
Most of them were _straight_ LPG on V8s.
If the installation is dual fuel, particularly on a injected engine,
then a small power drop is to be expected. This is very much a case
of the fuel injection being fairly efficient to start with.
In *stark* contrast, changing a carburetted engine to straight LPG
can achieve in the order of 15% _more_ power than on petrol!
Liquid injection of LPG will _always_ beat petrol for both economy
and power, but doesn't appear to be commercially available.
On my non-turbo 740 the
difference is so slight that I'm not aware of it in daily use. But it
may be more noticable on the turbo.
Generally, LPG has a higher octane rating and will be able to have
more boost without detonation. If the engine is set up for LPG, the
turbo system should actually respond _better_ to LPG than a normally
aspirated engine.
I read recently that the butane content of fuel in Italy and Greece
is much higher than in northern europe, and hence the octane rating
is lower...
The absolute fuel consumption will
increase some, maybe as much as 20% (LPG has only about 80% of the
energy value of petrol), but this is offset by much cheaper fuel.
The energy content, by mass: premium petrol (gasoline) 43.5MJ/kg,
average mixture of LPG 46.1MJ/kg.
In theory it should be possible to make an engine run on LPG much more
efficiently than it does on petrol, but in practice this is not really
acheived. Remember that you are converting an engine designed to run
on petrol, so there will be some compromises - in particular there is
no real chance of exploiting LPG's much higher octane rating.
Yes, there is, actually. Dual timing curve controllers, different
wastegate settings for the two fuels, cold air induction...
Other benefits include cleaner exhaust gases, particularly on pre-cat
cars, less contamination of the oil, and less engine wear. On a Volvo,
there is less in-car noise, too, because the underfloor fuel pumps can
be turned off.
Or, as in my case, removed completely. Of course, the 350 chev
makes much nicer noises than the V6 did.
I'd want to investigate the comment that town driving is best not done
on LPG. I can't think of any obvious reasons why this should be the
case. This is where some of the advantages of LPG are particulary
evident - fuel consumption is relatively high under these conditions,
so is engine wear.
The only thing that I've seen with some european convertors is that
they can freeze if you haven't warmed it up sufficiently from a cold
start and you plant it... Other than that, I don't know why this
suggestion would have been made.
Here in the UK the latest news is that the tax break given to LPG is
to be phased out over the next three years. But I console myself with
the thought that one reason I converted was so that I made less
environmental impact.
It is happening in Australia over 5 years, starting in 2008.
