To LPG or not to LPG...that is the question...

[Gavla]

So due to unforeseen circumstances I will be needing to increase my annual mileage from 3000 to 12000 for the next 12 months at least...

So I was thinking of installing LPG (prins system done properly)...on the basis it will be more efficient and cheaper in the long term (ie I do not need to drive like my grandmother)

and also put in a stainless steel longlife exhaust...mine is onthe way out and I need to sort out the broken stud on the manifold..

Thoughts and advice welcome...(constructive please...)

[Gavla]

e30...

[Topblag]

I'd talk to Brian Moore, I think he's the E30 LPG expert here IIRC.

I ran an e34 525ix on LPG for about 18 months and it was no bother at all. I didn't notice too much of a power difference between the fuels, but 175bhp at best isn't much to push a 2 ton permanent 4wd bus. Trick is to have cheap LPG nearby, as my 48L tank only got me 250 miles. I ran it from 160k to 185k miles.

To make the investment worthwhile you need to be sure the car will last and that if your life changes and you do less miles, the payback period isn't too long.

[Gavla]

Thanks Topblag...makes sense...

I figured if I am putting more miles on the clock it may be worth while doing it with LPG as I understand it is better for your engine in the long run...

Hopefully the legendary Mr Moore will spot this post and jump in...

[Brianmoooore]

No bore wash on warm up, no contamination of oil, greater safety from fire, can run the engine in a closed garage with no danger to health, half price fuel, no resorting to hidden software to pass emissions limits. Why wouldn't anyone run on LPG?
I see hints of the old myth have appeared in this thread, so I'll deal with that first. THERE IS NO THEORETICAL REASON WHY LPG SHOULD PRODUCE LESS POWER THAN PETROL.
The energy density of LPG is lower than petrol, in the same way that petrol has less energy density than diseasal, but that just means that the mixture ratio has to be decreased slightly, not that it makes less power. There have been a few competitors in the BTCC running on LPG in recent years, and they haven't been slower than any other comparable competitor.
If you modify your engine to run on LPG only, there is potential for a considerable power increase, by utilising LPG's somewhat higher RON than pump petrol.
The Prins system would be very nice, but in all honesty is complete overkill for a M20 engine. The Prins ECU creates an algorithm that modifies the petrol injector pulses to suit the gas injector flow rates, so as to take account of all the multiple sensors and multi layer mapping of the ECUs of modern cars, and relay all these inputs to the gas system. The standard M20 has a couple of basic maps, and only the MAF really controlling mixture, once the engine has warmed up, with a bit of correction from the IAT, and map switching from the TPS , plus, on most E30s, there is absolutely no feedback control to check if the above are doing as they should, so most of the Prins's potential advantages are neutralised.
An old type lambda feedback controlled venturi system can be fitted to an E30 as a DIY project, using a mixture of new and second hand components for £200 - £300 or so, and although this type of system theoretically does cause a small reduction in power (injection = air plus fuel, venturi = air including fuel), in practice, you're unlikely to notice any difference, and, depending on the condition of your petrol injectors and other components, you might actually get a power increase.
I drove around 100,000 miles on LPG with the red touring in my sig. and certainly didn't notice any power loss, even when using it for heavy towing.
When you get your new exhaust system, don't forget to have a boss for a lambda sensor included.

[Jona1971]

I love my LPG, no difference just cheaper fuel...

[DanThe]

If you have an E30 and an E46 why don't you use the E46 for the daily grind?

[Gavla]

e46 is a 330i so not that economical urban driving...also looking at getting rid of it so I don't need to pay maintenance and insurance on 2 cars...

[ThosO]

Was just thinking about this the last while. Has anyone run it with an m42 engine? i'll either need to sell the car and buy something more economical or go down this route in the next year and i know which i'd prefer.

[Brianmoooore]

No difference in "gassing up" a M42 to converting a M20. Doing a very slow restoration on a neon blue cab. at the moment, which will end up with a M42 running on LPG.