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ST-R LPG Conversion


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Hi Guys

Anyone had an LPG conversion done to their V8 especially the supercharged version.

Is it working alright? Rough cost! etc etc.

Mine is a 4.2 ST-R recently acquired on a 2004 plate



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seen a few forsale in the past

very expensive to fit and unless its a long term keeper, is it worth it

for what you save on fuel, is only going to cost you later on, lpg cars are known to cause valve problems



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Hi, I’ve just bought my 4th LPG. First a...Mondeo, then Range Rover V8 that I had converted, a Bentley Mulsanne  and just bought a BMW X5. I have never understood why it has not become more popular? Maybe I’m lucky that a LPG seller is just up the road. Never, touching wood, have had any problems with LPG and looking forward to saving money in the future!

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LPG is a lower octane rating that standard petrol, would never run any of my supercharged cars on anything but 99 octane fuel.

Why on earth would anyone want to convert a performance car to LPG ?

A professional installation is expensive and will take quite a while to pay for itself in fuel savings also, it is harder to sell an LPG converted car, many enthusiasts will avoid them like the plague.

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Marlowboy, Thank you for replying to my enquiry.

Clearly, you have knowledge of LPG conversions but do you use any particular make?

The Voices. I hear what you are saying regarding running a performance car on LPG and you are absolutely correct in many respects however, "Why would anyone want to convert a performance car to LPG" simple - COST. When cruising on a motorway, do you use the performance of your car - No so, why not use a lesser fuel effectively doubling the economy then revert back to petrol when you want to "play".



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My point is that the car was designed to run on fuel with a particular octane rating, adapting it to run on 'something else' seems to defeat the object.

The last thing that a performance car needs is sub standard fuel.

The cost of a reputable LPG conversion is going to be £1500-£2000, how many miles will you need to cover to repay the outlay ?

On top of this, you will not see any return on this expenditure when you come to sell the car, the majority of people who would consider the purchase of a used STR are not going to want one that has been LPG converted (partly based on personal opinion but also based on 20 years in the motor trade !)

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Hi Jon

Again, you are absolutely right and I totally agree with your comments.

My original enquiry was just to obtain valued opinions from those who has experienced LPG conversions and the pro's & con's of such conversions.

As you say, the cost of such work would have to be taken into consideration if only to rule it out.

We all know that the Jaguar V8 is a lovely engine but its not exactly renowned for its economy and I just wanted to see if LPG might have been a viable option as I do a fair amount of motorway driving.

Regards, Martyn


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Hi Martyn, I agree regarding the fuel consumption, mine averages 17MPG !

Not the most obvious fuel saving option I admit, but for the price of a good LPG conversion, you could purchase a second, more economical runabout to keep the miles off the V8 ?


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the following is from a Manufacturers manual......could they write this if untrue? 

The octane rating of LPG is higher than the octane rating of petrol, the difference is of about 15 octane number. A higher octane number signifies that LPG has a good anti-knock characteristics and a higher compression ratio. A higher compression ration means an optimise engine providing higher engine efficiency and power to weight ratios.

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I am only going off everything I have read over the years regarding a noticeable drop in performance when running 'performance' cars on LPG ?

Never heard of anyone fitting it to get improved performance, only lower running costs.

I did find this bit of info (but I am not a chemist !)

Generally there will be some loss of performance as LPG has a lower specific energy content than petrol, so more fuel is required to produce a given power figure, meaning lower economy. and more fuel in the cylinder, means less oxygen, resulting in lower maximum engine power

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.On a motorway, you don't use the performance aspect of any car but saving a few quid is worth considering.

I normally cover around 200-300 miles on motorways per week and with LPG around half the price of petrol, it had to be considered but not at the possible cost of a damaged engine and it is that which formed the basis of my original enquiry 

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There would  be a saving running on LPG due to the cost per gallon but the actual 'miles per gallon' figure is slightly lower compared to petrol. 

You could calculate the 'actual' saving for your mileage and then work out how many miles to cover the cost of the conversion ?

I am lucky in that almost all of my 40k miles per year is in a company car, fuel cost on my own cars isn't really an issue due to low mileage.

My advice would still be to consider a cheap diesel runabout to keep the miles off the STR, as the potential downsides of the LPG conversion would outweigh the benefits.

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Morning Jon

Based upon your advice and that of others, that is exactly what I intend to do. I have decided to keep my diesel S type as a work car and my STR as my "play" car.



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