LPG on E34 M5 and 540i

[bagpuss]

I've seen a few LPG-converted M5's and 540i's on uk-ebay lately - can they really retain their power on LPG ?

[RiggsyB]

It shouldn't make much difference lower down in the rev range, but i'd think it would really hamper the performance higher up in the rev range as LPG doesn't burn as fast as petrol.

LPG is really suited to larger capacity lazy engines, rather than the rev happy nature of say the M5. The 540i wouldn't be a bad conversion (in fact, given the price i've seen a couple of 540i's go for recently, that may be an option next year!) but i wouldn't do it to an M5

Incidentally, a while back my mate's dad had an otherwise standard E38 740i (4.4 litre) on a dyno... It made exactly the quoted 286bhp on petrol, but running on LPG it only lost 2bhp!

What would be interesting though is if you knew what you were doing, or knew someone who knew what they were doing, getting the car mapped with 2 different ignition maps (one for petrol and one for LPG) so that you can advance the ignition loads for when it's on LPG. Whilst it takes longer to burn, LPG has a higher Octane rating (typically 10 points or so higher) than petrol, so for a large capacity low revving engine, it could be used as a performance fuel! Especially if the compression ratio was upped a little bit too...

[bagpuss]

Incidentally, a while back my mate's dad had an otherwise standard E38 740i (4.4 litre) on a dyno... It made exactly the quoted 286bhp on petrol, but running on LPG it only lost 2bhp!



Thats a interesting test and tells me exactly what I wanted to know. Suprising though, I thought it would have crippled it, but not so !

[RiggsyB]

From what i'm told, BMW's are less sensitive to gas conversions than many other cars...

Though the bigger and lazier the engine (4.4 litre in a 740i is a lazy engine) the better...

[Yiorgos]

I read somewhere that to get the same amount of 'power' from LPG, you would need 1.25L of the stuff for every 1L of petrol.

Not sure what that says about how good LPG is for BMWs or for any other car, but here in Australia it's pretty well known fact that LPG doesn't give as much oomph as petrol.

[Michael999]

Im eager to hear if the M30 can go on gas or not.

[shogun]

The M30 also runs on LPG, quite a number of E32 owners of the German 7-forum have them converted.
Many have prins VSI installed. VSI stands for "vapour sequential injection.
I even know some people who run the M70 V12 on LPG.
http://www.prinslpgnetwork.com/
http://www.prins-lpg.com/en/prins/

[stx133]

I had a mazda 13B turbo rotary engine on dedicated lpg and was making 240Kw at 8,000rpm. get the tune right and power is there for the taking. it does require slightly more fuel per Km 10%, nothing like the 1.25x yiorgos suggests.

[CarloE34]

We had this conversation on a German forum and came to the conclusion that if you want to drive an M5 you need allso the money to drive it on petrol.
Second,you need to convert to Gas a LPI and not a LPG.
With LPI you don't loose any power and have no problems with a backfire.
But a M5 on gas??? No way Josè.:D

Afterall,this will be the same as the topic about the M5 badge,everybody has to diside for them selve;)