M5 running on gas

Brian · 12th December 2000, 14:17

Hi Folks,

Having driven a 1990 3.6 M5 for about 1 year, I then bought a 3.8 M5 year 1992 in 1994, which has been running fine since I bought it. Not to talk of the very expensive shocks, which I preferred to replace with a full kit from Schnitzer, which works great.

I will be commuting lot more kilometers next year and have been told of two owners of 91 M5's who had gas installations (LPG or GPL) and were happy with it. According to the dealer, they are supposed to encounter no problems when using the engine below 6000 RPM's. I would welcome any information on the topic! Depending on feed-back, I might consideer buying another car for commuting and keep my M5 for week-ends.

Thanks and have fun!!

NRL BITURBO · 13th December 2000, 21:31

Brian,

I am also considering this route with my Alpina B10 Biturbo. I am interested to note that you were advised that no problems would occur up to 6000 rpm. What happens above this limit? What is the typical cost of a conversion in Belgium as a matter of interest?

Regards,

Neil

Brian · 14th December 2000, 00:04

Hi,

What seems to happen is that the system is not able to deliver enough gas and that the engine will misfire causing backfiring, which I believe could lead to damages to the air intake parts. According to the feed-back I have received, this has not happenened but the owner had to stop and fit back some of the inlet accessories!

I have been quoted a price of 75.000 bf + VAT, which equals to +- 1.150 £ + VAT

Cheers,
Brian

P.S.: I would welcome any comments from M3 owners having gone the GPL way as the engines are pretty similar in design.

Quote:

Originally posted by NRL BITURBO:
Brian,

I am also considering this route with my Alpina B10 Biturbo. I am interested to note that you were advised that no problems would occur up to 6000 rpm. What happens above this limit? What is the typical cost of a conversion in Belgium as a matter of interest?

Regards,

Neil

Gene Cockrell · 14th December 2000, 04:45

High RPM/heavy load leaning (not enough fuel) is a great way to burn exhaust valves in a big hurry...It sounds from here as if this LPG conversion is not fully thought out...

raymondw · 14th December 2000, 11:56

Hello Brian,

Buy another car for the commuting work. With LPG, the M5 loses about 20%-30% power and that is a lot. Moreover, I have never seen a normal LPG fueled multivalve engine live longer than 200000km without problems to the cylinderhead and gaskets.

The problem is that with LPG, the temperatures in the cylinder head can rise to very high values and this causes high thermal stresses on the gaskets and the exhaust valves. Moreover an LPG conversion will make your M5 run lean and when at full throttle tho temperatures of the pistons and valves will rise dramatically. There are a lot of disadvantages of running lean, but the most important is that the temperatures in the cylinder head increase.

At full throttle, the DME of your M5 enriches the fuel/air mixture for a proper cooling of the the engine (exhaust valves, pistons). When running on LPG, that will not be the case anymore.

When your dealer says you shouldn't exceed 6000RPM with LPG, then he forgot to say also, don't give full throttle with LPG.

With best regards,

Raymond Woertman
1990 E34 ///M5
(Netherlands)