Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[tunnie]

Well i've just ticked over on 147k, so i've done 10k since it was converted back in late March, early April. In that time its never missed a beat, ran perfectly no EML errors, no poor running. 

For those that think you need cryptonite tipped spark plugs at £60 a set, you don't! Standard GM twins had already done a considerable mileage before LPG, and i've not touched them. Think i changed them at about 110k 

At this point i'd like to say another big thanks to Kevin Wood for drilling and tapping the manifold, LazyDocker for excellent front end work and spending 2 and a half days helping me convert. 

Of course i think its all down to the superb way the tank was mounted 

Cost wise, if get LPG at Asda which is currently 57p, its costing around 10p mile, with 90L tank (filling to 74L) i get about 370-400 mile range. Which is about the same as petrol, but this was costing me around 16-17p a mile. So in just a few months the conversion has paid for itself! 

Would i go LPG again? Sadly i think i would have to say no  - Sourcing LPG at good price is hard, Asda which is 11p per litre cheaper than BP is the ideal source, but their filling stations are very un-reliable often out for weeks at a time 

Filling up at BP, the savings are minimal, i find i am always looking for fuel too  :-/

With modern diesels being quick and economical, that will be the way to go i feel. 

[Field Marshal Dr. Opti]

This question has been asked before......but sadly I'm too thick to understand the answer fully.
Question.....Why does a car do less MPG on LPG?

[tunnie]

i have no idea why it actually burns more  :-/ - On a good day i get 25mpg on gas

[zirk]

Is it not do do with the Gas / Air mixture is higher (more Gas) than Petrol / Air in order to achieve similar running characteristics?

[Kevin Wood]

This question has been asked before......but sadly I'm too thick to understand the answer fully.
Question.....Why does a car do less MPG on LPG?

The volumetric calorific value of LPG is less than for petrol. In other words, a litre of LPG has less energy in it than a litre of petrol so you have to burn more litres to go the same distance.

It's a fundamental property of the fuel. No getting around it.

An engine designed to burn petrol will also be slightly less efficient at burning LPG because ignition timing and compression ratio won't be ideal for LPG.

Because of the huge price difference, it's still cheaper to run LPG.

Kevin

[tunnie]

This question has been asked before......but sadly I'm too thick to understand the answer fully.
Question.....Why does a car do less MPG on LPG?

The volumetric calorific value of LPG is less than for petrol. In other words, a litre of LPG has less energy in it than a litre of petrol so you have to burn more litres to go the same distance.

It's a fundamental property of the fuel. No getting around it.

An engine designed to burn petrol will also be slightly less efficient at burning LPG because ignition timing and compression ratio won't be ideal for LPG.

Because of the huge price difference, it's still cheaper to run LPG.

Kevin

Unless your filling up at BP, i calculated it was just 2.5p a mile cheaper 

[Dishevelled Den]

This question has been asked before......but sadly I'm too thick to understand the answer fully.
Question.....Why does a car do less MPG on LPG?

The volumetric calorific value of LPG is less than for petrol. In other words, a litre of LPG has less energy in it than a litre of petrol so you have to burn more litres to go the same distance.

It's a fundamental property of the fuel. No getting around it.

An engine designed to burn petrol will also be slightly less efficient at burning LPG because ignition timing and compression ratio won't be ideal for LPG.

Because of the huge price difference, it's still cheaper to run LPG.

Kevin

That's very interesting K. 8-)

Would there be much involved in developing an engine to primarily burn LPG in saloon cars and if could be done, would it differ much in design from a petrol fuelled engine?

Idle curiosity only.

[Kevin Wood]

That's very interesting K. 8-)

Would there be much involved in developing an engine to primarily burn LPG in saloon cars and if could be done, would it differ much in design from a petrol fuelled engine?

Idle curiosity only.

Not a great deal. You'd map the ignition differently, run much increased compression ratio. Forced induction would look a little more appealing. You'd probably map the engine ECU to run LPG directly.

The problem is the compression ratio would then preclude running on petrol, and with LPG stations prone to running out and slow to fix their pumps (I guess an LPG pump out costs them much less in reduced sales than a petrol pump out) life would be a constant struggle from one fillup to the next.

I suppose you could always carry a Camping Gaz cylinder for emergencies.

Kevin

[Dishevelled Den]

That's very interesting K. 8-)

Would there be much involved in developing an engine to primarily burn LPG in saloon cars and if could be done, would it differ much in design from a petrol fuelled engine?

Idle curiosity only.

Not a great deal. You'd map the ignition differently, run much increased compression ratio. Forced induction would look a little more appealing. You'd probably map the engine ECU to run LPG directly.

The problem is the compression ratio would then preclude running on petrol, and with LPG stations prone to running out and slow to fix their pumps (I guess an LPG pump out costs them much less in reduced sales than a petrol pump out) life would be a constant struggle from one fillup to the next.

I suppose you could always carry a Camping Gaz cylinder for emergencies.

Kevin

Thanks K - I suppose, like most things, it's a trade off between desire and practical application.

[zirk]

I thought you needed the petrol bit to heat the water temperature before the vaporizers could work properly?

[Kevin Wood]

I thought you needed the petrol bit to heat the water temperature before the vaporizers could work properly?

Yes and no. The vapouriser needs heat input to prevent it icing up but the real reason most LPG systems warm up on petrol is that the engine ECU enriches the mixture so much when cold (required because the petrol is slow to vapourise and clings to the walls of the intake manifold) that it runs too rich on LPG, which is injected as a vapour so requires no enrichment.

I have my system set to switch over at 20 degrees C coolant temperature or a minimum of 30 seconds running and it's fine.

As long as you aren't going to drive it flat out from stone cold (never a great idea) I'd say the vapouriser will probably get enough heat from the coolant for moderate rates of LPG consumption regardless of temperature. LPG boils at -40 after all.

You can also get vapourisers with electric pre-heating to help with cold starting.

The winches at our gliding club are LPG-only (crude mixer systems too) and whilst they are a little reluctant to start on really cold mornings it's not really a problem. The vapourisers are only heated by coolant on those.

Kevin

[TheBoy]

This question has been asked before......but sadly I'm too thick to understand the answer fully.
Question.....Why does a car do less MPG on LPG?

The volumetric calorific value of LPG is less than for petrol. In other words, a litre of LPG has less energy in it than a litre of petrol so you have to burn more litres to go the same distance.

It's a fundamental property of the fuel. No getting around it.

An engine designed to burn petrol will also be slightly less efficient at burning LPG because ignition timing and compression ratio won't be ideal for LPG.

Because of the huge price difference, it's still cheaper to run LPG.

Kevin

Unless your filling up at BP, i calculated it was just 2.5p a mile cheaper 

OK, so even in an emergency, and you fill at BP (and queue up to pay for the retards to serve), on your 140m round trip, thats still |£3.50 saving.  Thats under emergency conditions.

OK, so Asda out of gas.  One your commute, there is one in Bicester (Shell, 62.9p last time I filled there), and Cherwell Services sell it (at BP prices mind). Plus the BP in Brackley.  You are still saving.



Lets say Asda run out of petrol, or station closed. 112.9p for unleaded there.  122.9p for unleaded in Brackley last week.  Thats that same 10p per litre you are so reluctant to spend.



I like diesels.  But for the money that an Omega costs, inc converting, LPG wins for me.  Yes, there are odd times you have to, shock horror, run on petrol.  Even you will admit, these are few and far between.  Yes, you tend to be more organised with LPG, but is that a hardship?  You would still fill at Asda as its cheap, and you're tight, despite the fact their diesel is ropey...

[TheBoy]

I thought you needed the petrol bit to heat the water temperature before the vaporizers could work properly?

Yes and no. The vapouriser needs heat input to prevent it icing up but the real reason most LPG systems warm up on petrol is that the engine ECU enriches the mixture so much when cold (required because the petrol is slow to vapourise and clings to the walls of the intake manifold) that it runs too rich on LPG, which is injected as a vapour so requires no enrichment.

I have my system set to switch over at 20 degrees C coolant temperature or a minimum of 30 seconds running and it's fine.

As long as you aren't going to drive it flat out from stone cold (never a great idea) I'd say the vapouriser will probably get enough heat from the coolant for moderate rates of LPG consumption regardless of temperature. LPG boils at -40 after all.

You can also get vapourisers with electric pre-heating to help with cold starting.

The winches at our gliding club are LPG-only (crude mixer systems too) and whilst they are a little reluctant to start on really cold mornings it's not really a problem. The vapourisers are only heated by coolant on those.

Kevin

I think my 20C/10s is a bit ambitious.  On a hot day, that 10s just coincides with me turning right out of the works carpark

[tunnie]

This question has been asked before......but sadly I'm too thick to understand the answer fully.
Question.....Why does a car do less MPG on LPG?

The volumetric calorific value of LPG is less than for petrol. In other words, a litre of LPG has less energy in it than a litre of petrol so you have to burn more litres to go the same distance.

It's a fundamental property of the fuel. No getting around it.

An engine designed to burn petrol will also be slightly less efficient at burning LPG because ignition timing and compression ratio won't be ideal for LPG.

Because of the huge price difference, it's still cheaper to run LPG.

Kevin

Unless your filling up at BP, i calculated it was just 2.5p a mile cheaper 

OK, so even in an emergency, and you fill at BP (and queue up to pay for the retards to serve), on your 140m round trip, thats still |£3.50 saving.  Thats under emergency conditions.

OK, so Asda out of gas.  One your commute, there is one in Bicester (Shell, 62.9p last time I filled there), and Cherwell Services sell it (at BP prices mind). Plus the BP in Brackley.  You are still saving.



Lets say Asda run out of petrol, or station closed. 112.9p for unleaded there.  122.9p for unleaded in Brackley last week.  Thats that same 10p per litre you are so reluctant to spend.



I like diesels.  But for the money that an Omega costs, inc converting, LPG wins for me.  Yes, there are odd times you have to, shock horror, run on petrol.  Even you will admit, these are few and far between.  Yes, you tend to be more organised with LPG, but is that a hardship?  You would still fill at Asda as its cheap, and you're tight, despite the fact their diesel is ropey...

Of course, i'm lazy 

[TheBoy]

You could always ask mummy to fill it up .





Actually, thats not a bad idea, as then she would:
a) pay for it
b) have to tolerate the retards serving in BP Brackley