LPG conversion on 840ci sport

There ya go Steve!!...that told you, didnt it! ( )
Les

My wife has a X5 4.4 V8 and we have been looking into LPG conversion. I have developed the attached spreadsheet if anyone is interested in calculating the cost benefits for themselves.

unzip the attached file and you will get a html web-page spreadsheet.

Converter

Hi Angus

Does your converter calculate the fact if your car does 25 miles to the gallon on Petrol it will probably only do 17 on LPG?

LPG has a lower calorific value than petrol, I.E you burn more to achieve the same output as Petrol.

I know from experience as I run 2 x LPG transits for my business ( congestion charge exempt you see) and have done over a 40k a year in each, and yes they eat valves and cylinder heads ( i had to have a new head after 135K and a new engine @ 195K.

You need to budget 20% to 30% less MPG with LPG than Petrol, so pay back is a lot longer. You really need to be doing 30K a year to see a return, and i don't think anybody with an 8 will be doing that now being a classic rather than a Managing Directors Express.

It would be misleading to just assume the same MPG as petrol in your calculator.

Regards
Rob

Rob, your percentages are WAY out. I used to average about 23mpg in my 840, and now -on LPG- it does about 21mpg. And my driving style is distinctly 'happier' now that it's costing me half as much in fuel, so like-for-like, the difference is even smaller.

I have been running my 840 on LPG for about a year now. The conversion was done by a specialist in BMW/Land Rover V8 conversions, and I couldn't be happier with the result.

Re-reading these posts...I don't wish to offend, but I never cease to be amazed by the level of ignorance that is around re. LPG. However, hard facts completely de-base the scaremongering. Thanks for the clarification Paul!

In Holland (my birth country) LPG has been more commonplace for a long time, and attitudes to conversions (including those of 'petrolheads') are largely very positive.

Rob,
I was not aware that the MPG was adversely affected by LPG. Thank you for your informative post, based on real experience - I will incorporate the MPG reduction factor into the spreadsheet.

Loads of interesting posts.

I did a study on LPG some time ago:
The molecules have less bond energy, so less energy per litre and the reason it's taxed less is simply because the molecules have less Carbon atoms in proportion to Hydrogen atoms - so proportionally more water exhaust and less CO2.

You will still get smells from an LPG Cat equipped car - even I suspect one running on pure Hydrogen, as there are still oxides of Nitrogen (from the air) and many people confuse these smells with that of Hydrogen sulphide - rotten eggs.

The energy output differences are easy to quantify doing bond energy calculations, but very hard to quantify in practice as simple calculations don't take into account the many other engine, engine management and driving variables. Depending on these variables, consumption can vary a lot (so several of the posts with different claims could all be correct in their own circumstances :)).

The only certainty is:
If you don't do lots of miles, it will not save you money.

After that, "you pays yer money and takes yer choice".

Jaap

Zitat von Wildatheart;58001

Rob, your percentages are WAY out. I used to average about 23mpg in my 840, and now -on LPG- it does about 21mpg. And my driving style is distinctly 'happier' now that it's costing me half as much in fuel, so like-for-like, the difference is even smaller.

My figures were representative of my Transit Van experiences, i have no figures for the 4.4 Beemer motor, it was just an example so as not to mislead anybody, when i first looked at LPG i did not realise how much less MPG you will do, everybody assumes your car/van will do the same running on gas as petrol which it doesn't so this needs to be factored, in my case it was versus a diesel transit!

It also depends what sort of driving you do, white van man with 1.5 tonne in the back in London isn't very economic! Ford claim 30.8mpg for urban on the diesel motor transit, I know i have averaged on LPG 16.1mpg over 195k in one transit and 16.9mpg over 25k in the other. The maths do mean i have saved money over a diesel Transit - i did not have ton pay Ken Livingstone £1500 per year per van for starters

I assume your figures are calculated from litres purchased vs Miles driven and hand calculated over a decent period of time rather than from the OBC, as i don't think the OBC can calculate the LPG used as well as petrol - correct me if i'm wrong and your system has a plummed flow meter, (MY OBC for the transit says i do 150mpg!)

Out of an interest my OBC gives my current MPG as 19.9 (probably on less than 1000mls since i reset) and 17.8 on the second one which i have never reset and i've done 5K

The Debate will no doubt rumble on. With out a doubt if you don't do the miles it probably ain't worth the expense, the £2000+ it will cost is better off spent on some brand new shiny staggered 18" ALPINAS.

Regards
Rob

Politics

A good read....like watching the result of kicking a hornets nest...

There's one point missing....UK Politics....

Diesel used to be cheaper than Petrol - look at it now.
LPG/Autogas/Call-it-what-u-will used to be really cheap...but notice it's % increase in price relative to petrol over the years.

Henley & Marlow Rowing Club is watching it closely, mark my words....

Call me cynical, but motorists are an easy target.....

Zitat von robmarrs;58014

Ford claim 30.8mpg for urban on the diesel motor transit, I know i have averaged on LPG 16.1mpg over 195k in one transit and 16.9mpg over 25k in the other. The maths do mean i have saved money over a diesel Transit - i did not have ton pay Ken Livingstone £1500 per year per van for starters

Which means in reality it probably does 25 MPG driven gently, and closer to 20 MPG when being thrashed around town with 1.5 tonnes in the back. I've driven a few transits over the years, both petrol and diesel versions, and the fuel consumption has always been pretty horrendous in my experience. Probably partly due to me constantly thrashing it to get it to go anywhere, but who doesn't?

Incidentally, I average about 18 MPG in my 8 on a good tankful, and more like 15 MPG at the moment (haven't been near a motorway or any steady speed roads in a while). But with super unleaded down to 85p / litre, it's not actually that expensive for my 3-4k per year mileage, as I've again succumbed to the temptation to buy a second car for the daily thrash and trackdays etc

Saying that, I'm fully with Jaap on the benefits of dual-fuel cars if you do the mileage for it and it's done properly. Chances are your engine will actually last longer with it, as it doesn't contaminate the oil as much as petrol, nor does it leave carbon deposits everywhere. That whole issue of eating valves etc will never be an issue with BMW engines (or indeed 90% of the engines out there), as they don't make their engines out of chocolate unlike Ford. It's a well known issue that many Ford engines have valve seats that are very marginal for running on unleaded petrol, let alone propane (LPG) which burns slightly hotter. Ford themselves recognise this problem, they even make a replacement head that has been uprated for running on alternative fuels.

re. the Transits...the same LPG guru that did my conversion said that LPG was best avoided on Diesel engines. Out of interest, do you know what his reasoning for this would have been Paul?

Just read all the posts gents and for my pennies worth the 8 will never be converted v12 why should I? The 540? no chance - if I wanted to have LPG I would have bought a converted one.

The RR might be a possibility if I can get the feeling that LPG is the Devils fuel - just like Diesel!!!!!!!!

As far as the politics go Mr B and Darling have to screw us with fuel tax to hide their complete miss management of this country's economy -piss up and brewery spring to mind!!

Zitat von Wildatheart;58055

re. the Transits...the same LPG guru that did my conversion said that LPG was best avoided on Diesel engines. Out of interest, do you know what his reasoning for this would have been Paul?

Paul
My first LPG was a proper Factory fit buy from ford as an LPG van model, the second is after market. I thought all alloy heads have hardened valve seats these days to cope with unleaded, old cast irons have a problem! Pinto, Essex, etc.

Your MPG probably has something to do with being a manual i suspect and heavy right foot, my TVR has exactly the same problem

Jaap
If you have ever put petrol in a diesel engine you will know why you can't put LPG in a diesel engine.

Steve
Yep with you on the brewery front.

Regards
Rob

Zitat von Wildatheart;58055

re. the Transits...the same LPG guru that did my conversion said that LPG was best avoided on Diesel engines. Out of interest, do you know what his reasoning for this would have been Paul?

It's a much more complex conversion, as propane burns similarly to petrol (hence why it's pretty seamless in a petrol engine) but nothing like diesel. It can be done though, by injecting propane at the same time as diesel (the diesel is needed to provide the ignition, as there is no spark so the propane wouldn't ignite due to higher autoignition temperature).

The idea with the diesel engine is that the addition of propane allows the engine to produce significantly more power at lower revs, which means you use far less diesel. It can provide significant savings, but is totally different to the approach with petrol engines, making it more complex and therefore expensive. I think some high mileage fleet diesels have been converted, but I don't know much about it.

Zitat von robmarrs;58069

Paul
My first LPG was a proper Factory fit buy from ford as an LPG van model, the second is after market. I thought all alloy heads have hardened valve seats these days to cope with unleaded, old cast irons have a problem! Pinto, Essex, etc.

The vast majority of engines (since the introduction of unleaded petrol) have valve seals that are hard enough to comfortably cope with extended running on propane. If you look for used 7-series, you'll see lots of LPG converted models (both 8 cylinder and 12 cylinder engines) with intergalactic mileage and no hint of any head or other engine problems.

Ford are a well known exception to the norm, I think there are one or two Japanese manufacturers that suffer the problem too. Basically the heads are barely good enough for running on unleaded, and the extra heat of propane causes them problems over time. Even though they made factory dual-fuel models with revised heads that supposedly fixed the problem, it seems that your experience indicates that even the "propane compatible" head from Ford still falls short of the standard petrol head fitted to 95% of other manufacturers' engines .

Zitat von robmarrs;58069

Your MPG probably has something to do with being a manual i suspect and heavy right foot, my TVR has exactly the same problem

I doubt it helps! Even though the manual should be more efficient due to no torque converter (and BMW's pie in the sky figures agree with this), you inevitably drive the car harder with a manual box.

I have a stainless exhaust system with the centre resonator removed, so it's difficult to resist blipping the throttle and downshifting a few gears before entering a corner, before nailing it on the way out . It basically means braking more before the next corner and therefore wasting all my petrol energy on hot brake discs, but it sure is fun!

I checked the computer today, it's reading 16 MPG, which is actually an improvement from last week when it was at 13 MPG

Zitat von robmarrs;58069

Jaap
If you have ever put petrol in a diesel engine you will know why you can't put LPG in a diesel engine.

Partly true -- it's a completely different ignition system so can't be used as a replacement for diesel, but it can compliment it. See my previous reply.

Cheers