One alternative is LPG (or Liquefied Petroleum Gas) which is a natural and locally produced alternative fuel for vehicles and is roughly half the price of petrol.

So what is LPG? It is the generic name for certain mixtures of hydrocarbons, mainly propane and butane. When these mixtures are lightly compressed (800 kPa or 120 psi), they change from a gaseous state to a liquid.

LPG is colourless, odourless and heavier than air, so a chemical is added to give it a smell like rotten cabbage. In the event that even a very small leak occurs, it can be easily detected.

LPG burns readily in air and has an energy content almost as high as petrol, which makes it an excellent fuel for automotive use. In NZ LPG is extracted directly from ‘wet’ natural gas although it can also be obtained as a by-product of the petroleum refining process.

Running your engine on LPG is beneficial to your car as well as your pocket. LPG is a cleaner burning fuel than petrol, so engine life is actually extended. Engine oil and spark plugs need changing less often when running on LPG, so service intervals can be increased.

So if you happen to be like Paul (Sutty) Sutton and Lyn Marston who own a 1993 80 Series Landcruiser that is powered by a 5.7-litre Corvette engine, which averages 5.5 kilometres per litre, you look at alternatives seriously.

The vehicle was originally converted with the Corvette LT1 engine by the former owner (refer NZ4WD June 2001) although Lyn and Sutty have owned it for the past 2-3 years. If we have to get technical here the vehicle is Lyn’s, although Paul gets to do all the work on it.

They spent some time researching the pros and cons of converting the vehicle to LPG.

Vehicle logs had always been kept for the various vehicles in the family fleet, so they already had full details of the running costs of the V8 ‘cruiser and a Mitsubishi double cab diesel 4WD ute, which they also use for off-road driving.

A simple excel spreadsheet soon calculated all the costs over the annual 20,000kms for each vehicle, as well as a projection if the V8 was run on LPG. After taking in all costs for each vehicle including road user charges, servicing, registration, and fuel, it was no surprise that the petrol V8 was costing 0.352 cents per km, while the diesel vehicle was costing 0.247 cents per km, even though it was getting 8.4 kms per litre.

With their cost of LPG at 0.72 cents per litre, the V8 cruiser should only cost 0.173 cents per km, making it cheaper to run than the smaller diesel ute and about half the costs of for the same vehicle on petrol.

So, which one to have as the daily driver? The decision had already been made, prematurely, for Paul when he had a mishap off-road in the Mitsubishi and the insurance company claimed ownership.

Back to using the V8 as a daily runner, and internet research came up with an Italian designed LPG injection system that had been further developed by Sprint Gas Australia.

Seeking further information on the OMVL Dream XXI sequential injection unit, the Suttons were referred to Grant Miller of Autogas Technologies in Henderson. Autogas Technologies are the NZ agents and only properly trained agent-installers, approved by OMVL are allowed to install these LPG injection systems.

When Paul contacted Autogas Technologies, Grant just happened to be doing a similar conversion, on a BA Falcon, and he invited Paul to take a look. Most of the current conversions are on late model Fords and Holdens, as these vehicles also are a big part of the fleet market both here and in Australia. Many are being changed to LPG only.

Paul was convinced LPG was the way to go and that the Dream XXI sequential injection system was the most suitable for the high performance Corvette V8 engine.

As an engineer himself, Paul opted to remove the intake manifold and drill and thread the new injection holes in his workshop. He carefully calculated the position for the first one and drilled that making a jig at the same time to allow accurate drilling for the remaining seven injectors.

Now the manifold has two injectors for each cylinder. With the additional injectors fitted the manifold was put back onto the engine and a bracket made for mounting the 8 solenoids, that switch from petrol to LPG.

The injection unit also mounts on top of the manifold, so that each of the gas hoses is as short as possible and the same length.

In NZ you have to be a certified installer for LPG, so with the hoses suitably sealed the vehicle was taken to Grant Miller at Autogas Technologies for the installation of the tank, the regulator/vaporiser and ECU unit.

Paul wanted to keep the original fuel tanks in the Cruiser, so had a 100-litre LPG tank fitted into the rear load bay, behind the existing drawer system. This meant some modification to the drawer system (shorter by 300mm) but now the tank is completely out of view and with minimal loss of usable interior space.

Even the vaporiser and ECU and have been tucked away neatly, under the bonnet, so that at first glance the only indication that there is something different under the bonnet is the injection unit and solenoids on top of the engine.

Each of the solenoids has rubber seals to stop moisture and dirt from getting in and upsetting the electrical connections. The sealed computer has been mounted up high in the engine bay, behind the washer bottle.

In the past LPG conversions often meant reduced performance on both petrol and gas because the gas mixer was partially blocking the inlet manifold. With the Dream XXI, the mixer is completely eliminated thereby the engine’s performance is unaffected.

So, how does this sequential injection system work? The gas is delivered from the tank to the pressure regulator then supplies it at a constant pressure to the injection unit. This, in turn, is controlled by the ECU that calculates the correct injection time for each cylinder, as per the engine’s firing order.

The Dream XXI system ensures excellent vehicle performance on gas, without affecting the performance on petrol. The ECU integrates with the vehicles original ECU, leaving the engine set up unchanged and allowing it to switch back to petrol at any time.

The electronic control unit automatically and instantaneously switches from gas to petrol, if the engine stalls or the tank is empty. At start up the system also switches from petrol to LPG after a certain time and above a certain regulator temperature but only over a predetermined engine speed.

During installation a laptop computer is connected to the system’s serial port to download injection mapping parameters, specific to the engine, and emulates that into the LPG ECU.

Grant Miller of Autogas Technologies Ltd advised that a "standard conversion, on say a BA Falcon, is usually 2-3 days, but the Corvette Landcruiser wasn’t so easy." Suffice it to say, it was a tight fit to get everything in but the final result has certainly been worth the effort.

Driving the vehicle, we couldn’t detect whether it was running on gas or petrol and there was no hint or delay under normal acceleration when it changed over to gas.

The only way we could tell when it was on gas, was from the small electronic gauge inside the vehicle, which also shows the level of the LPG tank.

A simple light touch to the gauge manually changes over the fuels instantly. The only time we could be sure we were on gas was under hard acceleration when the pressure dropped at the regulator and the failsafe feature automatically changed to petrol and activated a warning buzzer.

This only happened at high revs in lower gears and due to the supply line from the tank not being able to keep with the gasflow demands of the engine. This was rectified with a larger diameter supply hose to the regulator, thus improving the maximum flow rate.

On the rolling road dyno a few minor tuning problems were highlighted. At first, it was running too rich but this was simply corrected. The earlier flow problem was revealed and, once remedied, the final output figures showed that there was absolutely no power loss at all from the LPG over petrol and performance-wise they were the same.

However, the rolling road dyno did show that a permanent 4WD Landcruiser loses a lot of power through the drive line, as the engine was only transmitting 130kW to the wheels.

Essentially that equates to around a 25-30 percent loss through the drive train. The other little piece of info was that, despite running a high flow K&N performance air filter, a further 10kW could be gained at the wheels by disconnecting the snorkel and air filter.

The LPG conversion, using the sequential injection system, costs around $4-$4,500 plus GST, on average. Pricing depends on the location and number of tanks and whether you opt for dedicated LPG or gas and petrol. The pay back on the conversion costs depends on you annual mileage and running costs.

Based on the figures Paul Sutton has done in his research (with some alterations for recent fuel price adjustments for both LPG and petrol) the conversion will have paid for itself in just under two years.

They also have further savings on
the cost of LPG by using a Rockgas Fuelcard which is similar to other fuel company cards but specifically for automotive LPG. .: