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V-Cheap V8

Magazine Clipping Article; Second Opinion on Running a V8 Disco on LPG/Autogas

The V8 that's v-cheap to run

Series II Discovery V8s are a bargain on the secondhand market, but could you possibly live with the hefty fuel consumption? You can have the best of both worlds with an LPG conversion, as David Holmes found out

All that money saved, and look - you don't even need to squeeze the nozzleMost Discovery buyers are faced with a choice between smooth, quiet power and enormous fuel bills from the Discovery's V8 petrol engine; or more economical driving with the higher noise and vibration levels of the 200Tdi diesel.

One solution is to convert the V8 to run on LPG (liquefied petroleum gas) as well as petrol. LPG took time to gain acceptance due to early problems with gas supply, reliability, safety issues and loss of load space. But, now, a properly designed and installed system can be a safe, reliable proposition for modern vehicles.

A variety of under-floor tanks are available. Systems are specifically designed for particular models and integrated with the ECU, giving multi-point sequential gas injection. LPG is now available at more than 1200 outlets in the UK.

No LPG system has been approved by Land Rover, suggesting warranties may therefore be affected on converted vehicles.

System improvements

Land Rover V8 engines have previously been converted with single-point injection systems, where the LPG is injected into the inlet manifold at a single point and allowed to enter each cylinder in turn by suction.

There have been problems caused by the large amount of gas at explosive-mixture strength in the manifold: a misfire could result in a blow-back into the filter box, causing major damage to the air filter housing. Such problems have been overcome through careful system design, but new multi-point injection systems are more appropriate for later engines.

The single-point system is an option for earlier Discos, but the engine management system of Series II models demands more sophistication. Modern multi-point systems use one injector per cylinder to inject the gas as close to the inlet valve as possible, reducing the amount of gas in the inlet manifold. Injection of the correct gas volume near to the inlet valve also improves efficiency and economy.

Making the conversion

The AG system in my 1999 Series II GS Disco uses one injector per cylinder and introduces gas through each injector in sequence. It's
controlled by a model-specific, dedicated electronic management unit piggy-backed on to the original engine management system.

Fuel under pressure from the storage tanks feeds to a vaporiser mounted in the engine bay, which then converts the LPG from a liquid to a gas, delivering it to the gas rail at slightly above atmospheric pressure.

Petrol is still required when starting the engine from cold and until the motor has reached normal operating temperature. As such, a specially fabricated, six-gallon petrol tank was fitted alongside the original fuel tank location: this also provides a fuel reserve of about 100 miles if the LPG tanks are run empty. The construction of this new petrol tank included the safety features of the original, such as rollover, non-return valves.

The gas control management system is fitted in the battery compartment, where it's protected from mud and water ingress. The only interior evidence of the conversion is a small multifunction switch added to the facia switch cluster. This displays the LPG content, allows the selection of gas or petrol, and displays a fault code if the system should develop any malfunction. The system will automatically revert to petrol if the gas runs out, sounding an audible alarm to alert the driver.

So, what's the bottom line?

During tests on- and off-road the converted Discovery returned between 13-15mpg on LPG, with no perceptible performance difference between the two fuels. The changeover from starting on petrol to running on LPG occurred after about three miles of warming up, and was only noticeable by the indicator display on the switch face.

Okay, so the original petrol fuel consumption of 18-20mpg (when driven carefully, falling to 15mpg around town or at higher speeds) was slightly better than with LPG - but great savings are made by the fact that, as I write this, LPG costs just more than half the price of petrol. Compared to diesel, it's even cheaper - less than half the cost. The low rate of excise duty on LPG is frozen until at least 2004.

Tests showed average costs of 20p per mile on petrol and 12p on LPG. My vehicle's full conversion, including all tanks, cost about 2940, meaning the system will have paid for itself after about 35,000 miles. From then on, it's very cheap motoring - but there are even more benefits to consider.

My overall verdict is that an LPG system needn't mean a significant compromise on space or driving range for the average user, and can bring the cost of running a V8 down to the same level as the diesel Discovery, for about the same overall secondhand purchase cost.

The V8 is a much more refined vehicle to drive, which is especially welcome on longer journeys - and it sounds fantastic, too. When the time comes to sell, you'll also be able to charge a premium, thanks to its LPG system.

Based on all that, my advice would be that if you are looking to buy a Discovery and are considering a diesel model, think again and try a V8. Just sit down and work out the comparative costs and savings - and I think that, once you have driven both, you might be converted. If you see what I mean.


Before committing your vehicle to a conversion specialist, it's vital to ensure the work will be carried out by a garage with a proven system and experience of installing LPG on your type of vehicle.

Before having any work carried out, you should check with your insurers - failure to notify them might mean your insurance is invalid if you subsequently have to make a claim.

An LPG conversion certificate is provided by the installer together with a service book, which should be routinely update with LPG- specific maintenance records. Converted vehicles should also display the recognised LPG symbol sticker in the windscreen to inform emergency services of the fuel type

The LPGA's website - www.lpga.co.uk - gives a list of accredited installers throughout the UK. But it's still important to confirm the  installer's experience and his track record with your type of vehicle. You should check the advertisers in LRO too.

Conversion costs can vary widely, so it's well worth shopping around.



Comment (By Teflon)

The conversion featured to in this article seems to have been a 'high end' professional one. It used a state-of-the-art, 'sequential' LPG injection system, and a convoluted 'substitution' tank arrangement, with twin LPG and 'reserve' petrol tanks, replacing the factory original. I would also presume that the tanks would have been latest generation 'multi-hole' valved items, matching what would have been a 'top-draw' installation of it's day.

That goes some way to explaining the relatively 'high' 3000 conversion cost, which the owner suggested he'd 'recoup' in around 35,000 mils at existing LPG & Petrol prices. I HAVE to criticize that comment; point of the article was that the V8 Disco suffered significantly grater depreciation than it's Diesel counterpart, but converted to gas was cheaper.

When the article was written, the Disco in question was still relatively new. Book price on the V8 (before LPG conversion) was probably in the order of 7,000, where a Diesel would have had a book value more like 9000. So 2000 of the 'conversion' cost was ALREADY paid for BEFORE he turned a wheel in it, by the saving over what h WOULD have had to pay for an equivalent diesel. But then he points out, that when he envisaged coming to sell the vehicle on, he'd expect his LPG converted example to fetch a premium over a non LPG example.

It's a bit of accountancy, I explain in "Gas-Guzzler?&, but you need to be careful how you 'amortise' your investment, if you want to make 'fair' comparisons. Original comparison was with a Diesel Disco, later one to a V8, and both showed favourable differences, BUT turn that around, and compare a 'converted' V8 at the beginning, and then compare THAT to a Diesel Disco at the end and the 'outlay' isn't so brilliant, but the fuel savings are better, and it's a 'fairer' comparison.

Basically, in the case of thee featured car, Purchase Cost + Conversion Cost, was probably about 10,000 for the V8, where a standard 200Tdi would probably have been about 9000; so Capitol Investment would have been 1000 more. Run thee car for three years, say 50,000 miles, and when he came to sell it, yes his converted V8 would fetch a premium over an unconverted example, but it would still be less than have got for a Diesel.

Ball-Park, that 9K Tdi Disco would probably have fallen to around 4,500. Unconverted the V8, would have fallen proportionally more, and be worth around 3,000. BUT, the converted example would possibly fetch a premium of 700-1000 on that.

So, doing a 'fair' comparison of the V8+conversion to a Tdi; V8 was cheaper to buy, but cost of conversion saw it about 1000 more expensive in total. At resale, the converted V8 then fetches about 700 less than a Tdi would. So over the period of ownership, the V8 has cost 1,700 more in 'CAPITOL' cost, than an equivalent Diesel.

Which means, when it comes to working out the 'pay-back' of being able to use the cheaper fuel; the 'savings' of running on LPG only REALLY have to recoup the 1700 of added capitol cost, NOT the full cost of the entire LPG conversion........Which is WHY I advise in "Gas-Guzzler?", to consider the conversion cost as a part of the 'value' of the vehicle.

However, couple of points I have to pick with the article;

Land Rover V8 engines have previously been converted with single-point injection systems, where the LPG is injected into the inlet manifold at a single point and allowed to enter each cylinder in turn by suction.

This is a bit confused. Systems that have LPG 'sucked' into the inlet manifold CAN'T be an 'injection' system! See Metering' The 'Charge' for detailed explanation of how carburettors and fuel injection works, BUT, I think that author was actually alluding to to 'Venturi Mixer' systems, from other comments.

Basically, 'older' (or less 'advanced, you can still get them!) LPG systems fed the gas into the inlet manifold through a device called a mixer, which worked like an old fashioned carburettor, metering the LPG into the air stream as the air flowed through it. Ie, the gas was 'sucked' into the engine, not 'squirted'.

Now, the 'injection' technology is exactly the same as the injection systems used for petrol or diesel, the only difference being in the type of injector used, to suit the fuel.

Ought to mention, actually, LPG-Injection, isn't 'strictly' injection. In a Petrol or Diesel system, the fuel is a liquid, and the 'Injector' is like a syringe; it's filled from a high pressure 'rail', then 'pumps' the measured quantity of fuel out through a nozzle, to turn it into a 'spray' of droplets in the air stream going into the engine.

In an LPG System, the fuel is a gas, at least where we want to burn it. It WAS a liquid, but we took it out of the tanks and put it through a vaporiser to turn it into a gas. If we put it under pressure, like we do petrol or diesel, and then tried squirting it through a nozzle, we'd just turn it back into a liquid again, and it wouldn't burn too well! So, the 'Injector' in an LPG-Injection system, isn't strictly an 'injector', it's more like a 'tap', that opens and closes to let a measured volume of gas through.

The system had fitted to the Disco in the article, was an electronically controlled 'injection' system, where the metering was done by an electronic brain working out how much fuel was needed, then positively squirting that into the manifold.

And because of advances in electrickry, his system had one 'squirter' for each cylinder, each one positioned close to the inlet port for that cylinder, and providing a 'timed' burst of fuel about when the inlet valve one that cylinder was open.

This is what is known as 'multi-point-sequential' injection, as there are 'multiple' injection 'points', and they are 'sequenced' to squirt at different times, and is what most 'modern' engines use. However!....

If you do look at Metering' The 'Charge', I comment on how the 'charge' in a 500cc cylinder of an engine comprises about half a litre of air, about on and a half coke-cans of the stuff, and a drop of petrol about the size of a pin head!

Measuring such TINY amounts of fuel accurately is very difficult, and to squirt in JUST that single drop of fuel for each 'bang' demands an electronic brain that can work out how big a drop is needed in about 1/50'th of a second, AND decide WHEN in that 1/50th of a second it ought to squirt it! Tricky job, made possible by the miracle of miniaturisation, that has given us high speed computing power, and electrical 'peripherals' that can work at the same rate and precision.

Back to that 'However'; BEFORE multi-point-sequential injection systems, we had systems that weren't 'sequential'. Rather than trying to squirt a single 'bangs worth' of fuel towards a cylinder each cycle, they mimicked a carburettor, and chucked fuel into the airs stream to maintain the mixture strength in the manifold, for the conditions the 'brain' thought best, depending on its sensors.

Didn't demand so much computing power, nor such delicate devices, and worked pretty well, particularly on smaller 'low-demand' engines where the quantities of fuel in question were that much smaller, and a single injector could more accurately meter the required amount of fuel than a bank of four. That is a 'Single Point' injection system, and there ARE 'single point'-LPG-Injection systems!

There have been problems caused by the large amount of gas at explosive-mixture strength in the manifold: a misfire could result in a blow-back into the filter box, causing major damage to the air filter housing. Such problems have been overcome through careful system design, but new multi-point injection systems are more appropriate for later engines.

Err, yeah!? I have to SORT of agree with this comment, but it's a bit emotive referring to a large quantity of 'explosive-mixture' in the inlet manifold! Sounds scary! But hold on a second, isn't THAT what the inlet manifold is for? I mean, it's where the air going into the engine is turned into a 'charge', we WANT it to be explosive, or it wouldn't go 'bang' inside the cylinder, would it!? And we need a 'large volume', 4.0l engine is going to suck in that volume of charge very cycle!

BUT, yes, the old LPG 'Back-Fire' is a bit of a bug-bear, and one of the 'quirks' of running on LPG. It's NOT a phenomenon that is exclusive to LPG converted cars, ANY engine can 'back-fire' if provoked enough, it's just that 'modern' engines aren't so prone to it.

The 'problem', as it is reported is greatest on 'Venturi-mixer' systems, which are not as 'refined' or sophisticated as LPG-Injection, and YES the a 'sequential-injection' system, controlling the 'charge' in smaller quantities, SHOULD be less hazardous. But, just because there is less to go bang, doesn't man its any less likely to!

It's a bit like my opinion of seat-belts, air-bags, side impact protection systems, crumple-zones, crash-helmets, motorcycle leathers, and fire extinguishers! They don't STOP an accident happening........... just how much it gonna hurt when it does!

CAUSE of the LPG-Back-fire is down to any of many causes, the same ones as cause a back-fire on petrol, only LPG tends to be a bit more 'eager' to back-fire!

Most common cause is incorrect ignition timing, and on older engines with points controlled - distributor ignitions, the engine going 'out of tune' or the owner getting the settings wrong, soon showed up with an LPG 'pop' through the air filter. Engines with 'stronger' more accurate 'opto' ignitions or full transistorised ignitions obviously more likely to stay in limits and not give a problem.

But, then I suspect that the out-of-sight-out-of-mind,  slack cam-chain, I am so fond of pointing out to people is also a significant factor in many cases where people encounter 'problems', and basically it comes down to installation and maintenance. Get it right and keep it right, and you SHOULDN'T have any major hassles! WHATEVER kind of system you have.

The single-point system is an option for earlier Discos, but the engine management system of Series II models demands more sophistication.

Sorry, but it doesn't DEMAND more sophistication at ALL! In "Gas-Guzzler?&, I explain how an LPG conversion is making your vehicle 'duel-fuel' capable, and that means fitting a secondary 'carburetion-system' to it to suit the alternative fuel. BUT, the ignition then needs to be optimised to suit whichever fuel you are running on, so you can adjust the ignition to work 'acceptably' for both fuels, incorporate some device that comes into play at 'switch-over' to change the optimum to suit the fuel, OR add a secondary ignition system to run in parallel with the secondary carburetion.

The 'Problem' has been that a 'tandem' ignition isn't always that practical; you cant run two distributors or have two sets of spark plugs in each cylinder, very easily! So the traditional way of contending with it has been to have some kind of 'ignition modifier. And cheap microprocessor have often offered a solution, interrupting the low tension signal to the coil, and re-timing it.

Modern 'integrated' Engine Control Units, with a brain, controlling both fuel injection and ignition, have made life 'different' for engine twiddlers, like me! But not necessarily more 'difficult.

As described in DIY LPG, it's quite possible to fit a 'Venturi-Mixer' LPG system to a fuel injected engine. Jacqui is an EFi, but she has a Venturi Mixer LPG system. Key is a little black box, called an 'injector 'emulator', which interrupts the signal from the ECU to the petrol injector, and in some cases the signal between ECU and ignition coil. It lets the ECU do what it does, but modifies the signals, so that when you switch to LPG, it stops the petrol injectors working, and modifies the ignition signal.

Now, as far as I'm aware, the only significant difference on later V8's is that they use 'distributor-less' ignition. Basically, each spark-plug has its own coil, and the ECU, decides when to fire one, which would make the job of an 'emulator' a bit more involved', and if you have a processor that is capable of modifying the multiple signals for the ignition, AND emulating the petrol injectors, then you MIGHT as well us it to control a set of LPG injectors! It's not 'demanded', it's just that it's 'easier' to us the higher tech solution!

Which is all well and good in an academic way, but not much help as these cars get older and the value drops to some-thing where they just DON'T demand a 3K conversion!

However; conversion costs are coming down, AND the systems available getting more sophisticated, and I have already noted some 'DIY' LPG injection kits coming available. Still not exactly 'cheap', but make the proposition more viable than a high-end pro-conversion; though they would probably gain a far higher spanner rating than the two Chris Perfect gave to the Venturi-Mixer system he fitted to an 'old' 3.5 EFi covered in  DIY LPG!

Probably THE most promising bits of 'kit' I have come across have been the 'Mega-Jolt' & 'Mega-Squirt' systems. Mega-Jolt is an entirely micro-processor controlled ignition system, the Mega-Squirt an entirely microprocessor controlled 'Engine Management System'.

You can buy these 'built-up' and ready to 'program', which is apparently pretty easy, and you can down-load pre-made engine 'maps' as your starting point, and then 'tweek' them from there to suit your own application.

They were originally conceived for people building 'tuned' engines, as a way of getting around the limitations of original equipment ECU's, when it came to 'chipping' them, but as far as 'Duel-Fuel' systems go, they have one VERY attractive feature; they can be 'Duel-Mapped'!

The future was originally to allow engine builders to have a 'safe' management map, but be able to switch to a 'development' map, and try it out or compare back to back or whatever. But, feature has been used by LPG converters to allow the same 'black-box' to run a 'petrol' map, and an 'LPG' map, when you switch between systems.

And from comment on the forum's, it would seem that 'those in the know' are finding ways to 'scratch-build' complete LPG-Injection systems, at a fraction of the cost of a pro-conversion, OR finding ways to make 'old-tech' Venturi-Mixer' systems work on more sophisticated modern engines. Technology, that I'm sure will drive more DIY friendly 'kits' and lower cost Injection conversions.

Mean-while, IF you 'bone-up' enough, you might b able to have a go at your own, 'scratch-build' LPG-Injection System, or 'Advanced Engine, Venture-Mixer System.........


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