1. Home
  2. Land Rover 4WD vehicles
  3. Interesting!
  4. Page 2

Interesting!

.mother>> Being one of those sad people who likes to keep very detailed records,

IC engines are like any other heat engine they convert the chemical energy in the fuel into heat in a compressed gas and then extract work from it whilst that gas expands against a resistance. You cannot odds the fact that lpg has 70% of the calorific value of petrol. So if it returns the same mpg and there have been no modifications to the engine then there must be another reason. This could take many forms from slightly less acceleration to a cruising speed meeting with a sweet spot of the engine or being a bit weaker at tickover etc.

I can get 15mpg on lpg from the 110 at a motorway cruise and 19 on petrol. On a general about town runaround the lpg drops proportionally more, I put this down to poor mixture control with the gas chokes, it still costs less than 66% of running on petrol. The single most effective measure to get the lpg engine to be more thermally efficient is to up the compression ratio but to make the best of this would require higher gearing. In fact lpg is rather wasted on the 8.12:1 compression ratio I have.

Still a lot better than my 2 1/4 petrol s3 which seldom bettered 14mpg with lousy performance to boot.

I only used to get 8mpg with the 101, petrol, which is one reason I stopped using it as a workabout vehicle, I admit I didn't make any concessions to the low gearing and aimed to keep up with other traffic.

Given the 101 slab front if you kept the cruising speed below 50mph and raised the gearing to give the same mph per 1000rpm I would expect to get similar figures as the 110 but people say that a 101 with tall gearing like that is sluggish, I cannot see why as they are much the same weight.

AJH

Reply to
AJH
Loading thread data ...

I'm in France - Euro sign not so obvious, sorry!

Euro rate currently around 1.22, so well above £1 / litre. With the euro rate as it is, I don't think we're too far different from the UK now in fuel costs. Bugger - no more gloating!! :( Still, at least diesel is cheaper than petrol here, by about 10c/l.

Matt

Reply to
Matt M

I fully understand the physics and chemistry and can agree that should you take two identical engines powering, for example, a generator with constant measurable load you may find LPG provides less power. However, my hypothesis factors different driving conditions and attempts to demonstrate that there are certain factors which influence when LPG is more efficient. Now, should one be able to correctly predict these influences one could logically program a system to switch and pre-empt them in order to correctly fuel the engine.

I would doubt, given the current technology when it comes to LPG conversions, that this would be feasible at present.

My conclusion is based upon my measurements and demonstrates that over the 4 year period currently analysed, there is NO discernable difference overall.

Notwithstanding, other conclusions are:

A 4.6L V8 is more economical to run in _my_ 101 Ambi than a 3.5L V8 and A ZF 4 speed auto box has made it slightly less economical - but far better for my health and wellbeing, so I can live with that.

I reckon my Ambi weighs somewhat more than a 110 and have a lot of roof furniture that one would expect to cause more resistance. My calculations are currently showing an _overall_ average of 13.8mpg.

This isn't as good as Simon gets, but Grumble does have a motorway 'sweetspot' of 68mph, which I try to maintain as whenever possible :-)

Reply to
.mother

You don't suppose his maths is off a bit do you ? BTW Does that ACU on Grumble give you a performance hit ?

Steve

Reply to
Steve Taylor

In message , . mother writes

LPG also seem to suffer less when towing IME.

Reply to
hugh

In message , AJH writes

Doesn't that argument assume that the engine is 100% efficient in each case and all the energy is released? Maybe with LPG being a gas is more efficient in using its inherent energy than petrol? I am no expert in this area so I may be totally wrong.

Reply to
hugh

I haven't seen the data he's working from. He could be spot on, but I'd possibly question the telemetry.

I fully expect it will do, when (cough) I eventually plumb it in... (I'm guessing at around a 7.5 to 19 percent hit, again, depending upon driving criteria and environmental factors. Quite a lot in real terms, but well within my 'comfort' boundaries).

Reply to
.mother

Has he got funny wheels or 'owt ? Still, its nice to have a target :-)

Tis a biggie fer sure.

Steve

Reply to
Steve Taylor

Well it does assume that the combustion efficiency is the same in both case, I'll grant the lpg should burn out cleaner as evidenced by lower CO and HC emissions but I think this has only a minor effect on heat in the combustion.

AJH

Reply to
andrew

The hope would be that the 4.6 had been developed a bit to give better performance, there must be 20 years of development between them.

Given the 3.5 was 9,35:1 and the later 4.6 was 9.6:1 there should be an immediate improvement if pulling higher gears.

Once the ZF has locked up does it still have more losses than a lt95?

In fact what is the overall gearing difference between the two boxes, often autos will have higher gearing than equivalent manual boxes and the 4.6 should be pretty long leged in a range rover, the lt95 in a 101 had the lowest set of transfer gears fitted as well as the higher ratio diff gears.

Does your lpg set up start as well as run on lpg?

I always start and run on lpg unless I've got an empty tank so my figures are full to full with no petrol used between, if I start on petrol from hot I can travel about 1/3 mile on what;s in the carburettor bowls.

Reply to
andrew

On modern SGI systems it seems to be roughly 80-85% of the petrol economy. My 5.7V8 Chrysler does 26.5mpg on a long run on petrol, roughly 21-22mpg on LPG. At the price I pay for my LPG that is equivalent to 44mpg on diesel - the diesel version of my car only does 38mpg on a good day! I always compare LPG against diesel not petrol - let's face it, if you don't have a petrol engine on LPG you'd go for the diesel. My DII did 15mpg on LPG which at the time was equivalent (£ per mile) to

29mpg on diesel - I doubt if an auto TD5 would have returned 29mpg under anything other than extremely economical driving styles. Badger.
Reply to
Badger

Where did you put the tank(s).

Reply to
William Tasso

Ours has the replacement dual fuel tank jobbie giving ~75l LPG and, erm, whatever space is left for petrol. D1 had cill tanks, but course the D2 has all the gubbins down there for ACE an the like, so no space for extra LPG tanks.

On a long run the LPG-POI for the TomTom is handy :-)

Reply to
.mother

Ahh - didn't know there was such a thing. Ours is a D1 - this needs investigating.

It's a silly place on an off-road vehicle anyway.

I bet.

Reply to
William Tasso

You could always fill them with WD40 ;-)

Reply to
.mother

ha ha ha

btw: found this

formatting link

Reply to
William Tasso

Have you tried the rubber glove and pop-bottle solution?

Reply to
.mother

Well it's Friday night, you have to live a little!

Reply to
Ian Rawlings

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.