M5 (E39) + LPG = Sacrilege?

[Zwolf]

I seem to recall a few of the owners of these on here have converted their M5 to run LPG for higher mileage use.

I'm considering the same, albeit on an as yet unbought example, or simply converting the E38 750i I currently use, as a result of moving and having a 100 mile/day commute of mostly A-road and motorways and pathologically opposed to going diesel. As good as a 530d is, it just isn't remotely special in the way a V12 or M V8 is during driving time away from the commute.

Some may consider it a "waste of an ///M car" and the Seven better suited to the role, however I only have one space so a choice must be made and stuck to at least for as long as it takes to justify the cost of conversion, but ideally a situation I'd be keeping for at least a year or two and 30-60k miles from present mileages (currently 120k on the Seven, looking at M5s in the £7-8.5k range, mostly 120-150k mile examples, provided current mechanical condition is sound).

[Zwolf]

sydown said:

I have run a e39 540 m sport on LPG for about 5 years now and will only get rid when it really fails 190K miles so far! The two cars you suggest are problematic as only prins or brc injectors will cope with the 50bhp per cylinder of an E39 m5 without running lean at top end and the 750 will be expensive to convert as you will probably need 2 V6 kits to convert!! My mate runs a E60 550 on brc and at 367 bhp the car does get a tiny bit lean at full throtle on full load! However when you need to you can always switch back to petrol in less than a second!! I used Solihull autogas for my conversion and the chap was happy to give as much advice as possible before i commited to anything!

Interesting stuff, thanks. Having spent most of today smoking around in the E38, I'm in agreement with most here that it's the more suited and sensible one to convert and I should wait until home and work are closer together and just enjoy an ///M as it should be.

The running lean at top end I'm not too concerned about in either case as when it's running on LPG it'll just be cruising along ad normal motorway speeds, below 3k most of the time and the V12 isn't about it's top end really. It'll be run on unleaded sometimes too, to keep that part of the car's mechanicals running as they should and hopefully preclude the tank turning to Swiss cheese, a particular E38 problem.

Cheers chaps, sensible decision reached. The most local company I've found - as recommended by a neighbour - is Capital Auto Gas in New Malden and they seem to use BRC kit. I requested a quote for a 12 cylinder installation as they only list 4,5,6 and 8 on their website. Three days later I'm still waiting for contact. Not too impressed at that.