Technical LPG Conversion ?

[bmcecosse]

Has anyone converted their Punto Grande to run on LPG ? keen to hear reports of how it runs on LPG - and what MPG it gets!

 

[Most Easterly Pandas]

What size engine are you wanting to get info on. Not many LPG runners on here, but I'm able to help if you have any questions.

My 1.4 16v Stilo returns 30-32mpg on LPG.

 

[bmcecosse]

Thanks! It's the 1.4 Punto Grande. Doing ~ 44 mpg on petrol at the moment. Would be hoping it would do at least 40 on LPG? Is that too much to hope for ? I thought these modern LPG 'injection' system got much the same on LPG as on petrol ?

 

[Mr Wild]

Why the quotes around the word 'injection' ?

I fancied converting myself but after reading about it thought it was too much hassle, think I'll just go for a diesel and run it on veggie instead when I get the opportunity to upgrade.

My thoughts were, too much faff to bore out the additional injection ports, wasn't sure how you could have your ignition on and just bypass the on board ecu without affecting essential systems but didn't read into it enough, presumably they just tap into existing crank and O2 sensors, you get reduced BHP from LPG so knock 10% off 59bhp and you've got a scooter, additional weight from carrying the tank and all the bits and pieces, price of LPG is shooting up anyway feel you're getting screwed over with tax in this country no matter what fuel you use. Wasn't sure how it affected the price of the vehicle after doing the upgrade, is it really a selling point, are many people interested in this when looking for a car, would it put people off?

So I'd be interested to hear your motivations for upgrading.

 

[DaveMcT]

LPG has less energy per litre than petrol so unlikely to get the same MPG. UNless you do humungous mileage the conversion costs make the whole idea hardly worth the hassle.

Be careful with diesels on veggie oil. They are fine on biodiesel (methyl ester) which is veggie oil with the glycrol removed, but unless the fuel is pre-heated plain veggie will clag up the engine. Glycerol burns too slowly to work safely in modern diesels though it is ok in the older prechamber engines.

I have run a car on home made biodiesel. It really is a great fuel, but its a major hassle to make.

 

[bmcecosse]

'Injection' - because some seem to inject gas - and others liquid LPG ! It does indeed have less calorific value - BUT - it has a nice high octane rating (108 -110) and the modern engine can take best advantage of that by advancing the ignition timing. The older 'suck in' systems (with a venturi) did suffer power loss - but part of that was the venturi restricting air flow. I thought the modern systems were just about same power. But them - I'm looking for economy - I never use all the power anyway!
If I want to go fast - I use my TR7!!

As for cost - LPG seems to remain ~ half the cost of petrol. Each time petrol goes up 2p - LPG goes up 1p. So the 'savings' are growing all the time! So petrol around here now 114/litre - and LPG ~ 56p/litre. I reckon I will save about £15/£20 per week - and be less worried about using the car. Been quoted £1000 to do the work. And as fuel gets even more expensive - I reckon a second hand LPG car in a few years will sell very well! They go like hot-cakes at the moment!

 

[DaveMcT]

To make proper use of the high octane the engine needs a high compression ratio, but that would prevent it running petrol.

I've just found the energy figures not as bad as I thought...
Petrol = 32MJ/L, Autogas = 26.8, so near enough 84% that of petrol.

A rough calc puts LPG at about 35% cheaper per mile than petrol.

The only snag is that when it gets popular the government will put up the tax. Diesel was put up on the excuse that its more dirty then petrol. Todays diesel fuels and the engines are less polluting than petrol but they dont get any tax discounts.

 

[Most Easterly Pandas]

Thanks! It's the 1.4 Punto Grande. Doing ~ 44 mpg on petrol at the moment. Would be hoping it would do at least 40 on LPG? Is that too much to hope for ? I thought these modern LPG 'injection' system got much the same on LPG as on petrol ?

Well my 1.4 returned an average of 34-36mpg on petrol, So I'd have estimated 36-40mpg on LPG for you based on experience. Possibly a bit more.

LPG has less energy per litre than petrol so unlikely to get the same MPG. UNless you do humungous mileage the conversion costs make the whole idea hardly worth the hassle.

Humungous mileage? 20,000 mile brake even on average (all cars are different though), improved residuals, and ever so slightly cheaper RFL.

Mega miles is a tad OTT. LPG will certainly start paying for itself faster than a DERV over its petrol counterpart.

'Injection' - because some seem to inject gas - and others liquid LPG

I don't know where you got that from. All LPG systems inject gas vapour. All vehicles are normally fitted with a vaporiser intergrated with the vehciles coolant system for the converstion of LPG from a Liquid to a gas/vapour.

Its due to this that LPG run engines tend to run better in as far as instead of a liquid being injected as a fine mist to be ignited as per petrol fuel, LPG is already in a gasious state, and results in a better burn.

 

[bmcecosse]

Thanks MEP. I thought the injection was done with liquid fuel - I had a Vectra years ago on LPg, and of course that had a vapouriser, and the venturi/suck in system. It was fine for a while - and was almost half the cost to run on gas (I found a very cheap supply place!) - but then it started going wrong with 'explosions' under the bonnet when starting. Wife refused to drive it - no-one could fix it (original installers had gone bust) - so I reluctantly traded it. But over the two years I had it - we saved about £1000 running costs - after paying for the conversion. If i can get 40 mpg on LPG I will be happy!

 

[Most Easterly Pandas]

You say cheap suppier. Who/what were you using? Wasn't bottled LPG was it, as its differet to auto gas in that auto gas is taken from base of tank and most other LPG is from the top.

Thus auto gas is filtered more to remove heavies from it that will normally collect at the base of a tank. Ok in bottles as it doesn't get sucked out, but if that gas is used in a car, small bits may begin to collect and cause issues.

Also, can you remeber the brand of LPG system installed, as some are renowned for not lasting, and others will seem to go on forever.