Go LPG! Research - Jaguar V12's

Jaguar XJS V12 and V12 XJ saloon models



The XJS and XJ12 range begins with uncatalysed cars utilising the 5.3 litre V12 right through to the 6.0 catalysed versions made until 1996. They are magical cars and seem to be ideal conversion candidates as they have relatively high fuel consumption, but like many things in life, it just isn't that simple........

Early (uncatalysed) 5.3 litre cars

These engines can be converted very well with our inductive mixer (Open Loop) LPG system. It is NOT correct to call this installation 'Single Point', as it must be dual (or twin) point with 2 mixers feeding LPG through the 2 throttle bodies. The twin 6 cylinder banks of the V12 require it to be treated as TWO separate engines if done properly, meaning that two components (e.g gas mixers, vaporisers etc.) must be used instead of one of each for a 6 cylinder conversion.

There is always a small risk of backfiring with an inductive mixer system as the manifold(s) are filled with LPG / Air mixture, and if that mixture is ignited in some way, backfiring is often the result. This cannot happen when a multi-point injection system (often misnamed 'SGi') is used as there is only air inside the majority of the inlet manifold when LPG is injected into a similar location to that used by original petrol injection system.

All XJS models are petrol injected, and the same goes for all V12 300 models. Some of the earliest examples (along with most of the XJ 40 model V12's) may be uncatalysed, but that's largely irrelevant as the catalyser's main function is to reduce emissions. The only significant difference is that the closed loop fuelling control system which goes hand in hand with a catalyst will also be missing, but that does not mean we cannot use an LPG injection system - we still have electronic petrol injector signals required to run the LPG injectors. The alternative to an inductive mixer system is therefore a multi point LPG injection system, but that is still subject to the constraints listed below for Catalysed cars.

In either case; The increased amount of equipment fitted, the difficult and cramped working conditions take their toll in terms of time spent. We can convert THREE 6 cylinder cars in the time it takes to do ONE 12 cylinder. Go LPG will do the job for you, but be ready for an inductive mixer conversion cost of at least 2200.

Catalysed 5.3 litre cars

The open loop conversion described above can be made closed loop with the addition of two computerised feedback control systems (OMVL Millenium).This can give all that a catalysed car needs at less cost (2500) than an injection conversion. However, note that the risk of backfiring (described above) still applies. The alternative is a multi point LPG injection system but that is still subject to the constraints lited below for Catalysed cars.

Catalysed 5.3 and 6.0 cars

6.0 litre cars should only be converted using Multi point sequential injection systems as they are the only V12 models using genuinely sequential fuel injection*. All older modes have an 'half group' injection strategy and are not sequent. Some owners have a preference for a multi-point injection system for a catalysed 5.3 model to remove any risk of backfiring. To cater for all of these applications we have two ways of installing a multi-point injection system, but first, the background....

The problem with a multi-point injection system is that conversion equipment manufacturers will only make the systems they can sell most of. None of them make 12 cylinder conversion equipment (by and large, just the 12 channel ECU) because so few 12 cylinder cars are currently in production. Large volume car manufacturers no longer make a V12 engine variant at all, Jaguar and BMW withdrew theirs V12 a while ago and a s result the V12 conversion market is tiny. As a result, only 3, 4, 5, 6 and 8 cylinder SGi systems are made by the major LPG equipment manufacturers.

Where does this leave the V12 owner?

At present, there are 2 ways to get around this problem - Either;

Use a modified multi-point injection system which uses a single 6 cylinder ECU to 'fire' 2 injectors at once (making 12). It is a good solution but beware that the ECU manufacturers will NOT warrant the ECU against any fault because it is firing two injectors instead of one, it is being put to a task it was not designed for. Likely cost for this system is around 2700 with a single cylinder tank and no ECU warranty.

-OR-

Have 2 x 6 cylinder multi-point injection systems fitted to work in tandem (remembering that we have to buy 2 complete 6 cylinder front end systems, fit them and wire them up in tandem) and run both from a single switch and tank. This is the best way to do the job by far, but bear in mind that the cost of a 6 cylinder multi-point injection conversion is 1850. To convert a V12 in this way we must fit TWO of those (save the second tank and filler).

Cost of the 2x6 conversion is around 3,200 with a single tank. *Note that if you choose to go down the 2 x 6 cylinder multi-point injection systems route for an X300 V12 car, that will give truly sequential LPG injection in a way that is impossible with the single 6 cylinder ECU method.

V12's are certainly not cheap to convert in any of the ways described above. They are not even cheap to run on LPG when set against a comparable 4 litre X300 or XJ8 models, although running a V12 on petrol only could be a fast track to bankruptcy. It must be remembered that even the best quality V12 cars are exceedingly cheap to buy and no other model drives quite like the turbine smooth V12 Jaguar masterpiece. The Man who buys a V12 certainly gets a whole lot of car for his money and if you have to have one, you have to have one, nothing else will do.

There is another way of looking at conversion cost, The relatively high V12 fuel consumption actually makes 'payback' of the conversion cost a lot closer. LPG conversion is the only way we know of transforming the mighty V12 into a usable, affordable and everyday car.


There isn't much space.

Fitting two multi-point injection 'front end' systems in the cramped space takes many times
longer than fitting two seperate systems to two 6 cylinder cars.


If you decide to have your V12 converted and have read and understood the costs involved, call Go LPG. We have more experience with V12's than most converters.

Expensive it may be, but running your V12 on LPG will save you an absolute fortune..........


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conversion of your XJS or XJ12

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