I have a SL300-24 on LPG, I can tell you you save a shitload on fuel let's make a Quick calculation:
I use with my driving style 15 litres of unleaded 98 at 1.3 euro/litre (3feb07price) which comes to 19.5 euro for 100 kilometres.
With LPG I use 22 litres at 0.5 euro which makes 11 euro's so the difference is 8.5 euro for 100 kilometres. (beware this is full throttle I can do with less but there is also less fun ;-)
I have a a ringtank in the place of the spare wheel (no trunk space is lost) which can be filled up to max 50 litres so I do have to go for LPG quite often but there is a fuel station nearby and I get stamps for a free carwash so I don't mind. The refilling hole is hidden behind the licence plate.
It drives on 90% of the available power on fuel. I have had some minor problems with it, for example driving 200 km/h or more suddenly the LPG couldn't take it anymore so I had to slow down to 160 and than it was ok again, it did this sometimes, other times it was ok.
The installation was from IMPCO it was LPG because my '93 SL still has the old KE Jectronic injection.
I now have bought a newer ('94) M 104-320 engine, a eaton M62 supercharger, and a S 350 Turbodiesel crankshaft to increase cc's, new engine management DTA-fast now to boost performance, I will also install a newer LPI system from Prince (LPG with direct injection) the DTA engine management will be able to control either the fuel and the LPI. (I am having it done, talking big bucks here).
As far as pro and contra LPG, I don't mind spending a big amound once and then saving weekly, or at least every time at refilling. Going for fuel and paying 100 euro's is getting absurd nomatter how much money you have, it has nothing to do anymore with rich or poor just common sence.
For as far as the engine goes, M104 is one of the strongest engine Mercedes ever made in regard to durability and it is very good on LPG, you do need, however, somebody that knows about these engines to install it.
I will give an update on how the project goes, I am hoping on 330+ hp's.
Someone actualy did convert a 1998 SL280 to LPG. It is for sale in autotrader.co.uk . I was kinda interested in it but didnt enquire at the end of the day. I bought a 98 280 in Nov.
As most of the replies are speculation, (no disrespect to anyone of course), Id say your best option would be to contact the seller and go and look at it and enquire who did the conversion.
The link is here, Autotrader - MERCEDES-BENZ SL280 Convertible
Just spotted the previous post on an other actual conversion. I stand corrected that no one else had done a conversion. If you find out where the LPG conversion was done on the one I posted a link to , id be interested to know.
Colm
Dublin
@ coba
The IMPCO installation was done by a guy here in Belgium, it costed 2300 euro's it was done by T.C.V. ( Izegem Belgium ) here is his mail address t.c.v@pandora.be his name is Hein Demasure (very clever and big knowledge about these engines)
For your car you can use the Prince system wich means that no power will be lost and you will not have more gas consumption because of the injection. (so even cheaper driving) Price will probably be comparable to the 2300 euro's (1,549 GBP)
i can't understand why you guys want an LPG gas in your sl. on my opinion its really crazy if you ask me. if i want a sports car with a cheap gas. go for a honda or something. cheaper in every way. parts,car,service,gas, name it they are cheaper. you can even play with anything put lpg,put even garbage like the one in the movie back to the future. you might even become an inventor for playing around them.if you are to replace it with lpg system that you dont even know if it will work. why not buy a toyota engine, replace it with the sl engine. keep the engine so that when its time to sell it. you can have better price in selling it. but then again this is my opinion. dont hate me for it.
try this one for kicks, drive any other car you have. sit on it. drive around your city. stop for awhile. and close your eyes and imagine that you are driving an sl. you can even think your driving a ferrari. it feels good and it feels very cheap. like i said dont kill me just want you guys to smile and badmouth me while your laughing in your chairs.cheers guys!
Well I know you guys will hate me but I've just had my 600 SL converted to LPG!!
It cost me £2300, but to counter that LPG is 42p a litre where I fill up, as opposed to 95p a litre . Mileage on petrol is around 20 to the gallon and on LPG is around 16. Performance for most driving is perfectly adequate (they reckon 95% of power on petrol), the system is fully automatic (i.e rins on gas whenever possible, but switches to petrol when needed) and if I really want to hoon around I just tuch a button on the dash and revert to running on petrol.
Ok, I have lost my spare tire and the soft top pump is now relocated and sits above the battery in the boot. i carry a couple of tins of "tyre Weld" in case of a puncture (and keep my roadside assistance fees paid).
In day to day driving I can't notice the difference in driving on gas to petrol, and it nows costs me £15-20 to fill up instead of £70. Admittedly I get only 150-170 miles on gas from the tank, but that fits in nicely with my round trip to work, and there are now 1300 filling stations in the UK anyway.
I cant find any reason not to commend you on this conversion, I have considered this myself as here in Western Australia you can get 2 grants totaling $3000 for a conversion making it a freebee. In the UK The price of fuel is so expensive that it is compelling to get it at half price, can you now drive in the London congestion zone without paying the £8.50 daily charge?. I have gone as far as making online inquiries over here but have had no response so far. As fuel is cheapish and I dont do to many miles I am not in any hurry but If I can find someone who can do it I think I will give it a go.
Wayne, for a one off registration fee of £10 you avoid the daily congestion charge. That only would save me £1600 at least if I went into London daily (not that i do but even twice a year and it would save me money. Converting the V12 to gas is a little more troublesome than the smaller engines because of lack of space. I have had to lose both my airboxes (replaced by K&N cone filters) to make room for the evaporators, and the car is going back next week to have a larger supply pipe fitted as it struggles (fails) to supply enough gas on full throttle at higher revs and it swaps back to petrol (automatically).
R129 300-24 on LPG 
Linear Mode
