Hi,

I just saw the excellent calculator by "PoweredByCNG".

What is the correct figure for the additional consumption of LPG, compared to unleaded petrol, for:
- mixer systems ?
- gas injector systems ?

(expressed as a percentage)

I keep hearing different figures.

One service centre told me it was 20% extra consumption for the mixer, and 11% extra consumption for the gas injector, compared to unleaded petrol.

Thanks,
Richard

There is no simple answer to your question.

The fuel consumption penalty really depends on how well your system is installed and calibrated.

The injected systems (particularly Liquid Injection systems) are more efficient and provide better performance and smoothness. They also reduce the wastage of fuel due to the inaccurate nature of single-point fuel metering associated with mixer-based systems.

In short, here are the figures I go by:
Mixer: +35%
Gas injection: +25%
Liquid injection (JTG): +20%

Regards,
Dave

Thanks for your reply.

It's for a 1998 Commodore VS ex-ambulance.

Having read some of the horror stories people have had with Commodore V6 engines and LPG, I'm actually starting to wonder if I want to do it at all!

In your opinion, would you avoid gas for this engine ?

Thanks again.

The Ecotec engines last hundreds of thousands of kilometres on gas as proven by taxi drivers all around Australia, although they don't last quite as long as the Falcon I6 unfortunately.

My advice if you want to go ahead with a conversion is to go for an IMPCO carburettor system with a model 225 air-valve gas mixer. Make sure it's a GENUINE IMPCO system and in particular, look for installers who use the lean-bias processor. Change your spark plugs when you have the system installed to a brand new set of cheap NGK coppers gapped to 0.7-0.8mm and replace every 15,000km and it'll be happy days.

Regards,
Dave

Thanks heaps for that.

I was at the point of giving the whole conversion a miss.

Interesting that you suggest a mixer system, but not vapour or liquid injection.

Is that because the extra cost is simply not worth it?

Or because there are additional tech issues with injection on this engine?

Thanks again for your advice.

Regards,
Richard

Injection isn't worth it for pre-VZ or pre-BA unless you have a REALLY good VX-VY or AU (i.e. low kilometres, showroom condition inside/out, etc.). There's no point installing a gas system that's worth about as much as the car.

Another issue is that there are no injected LPG kits designed for pre-VY as most distributors focus their efforts on cars made after 2003 as these require emissions-certified kits whereas older models do not.

Find a reputable installer who can install a Genuine IMPCO system with lean bias processor (this is VERY important), change the spark plugs every 15,000km with NGK copper plugs gapped to 0.8mm and you'll have very few issues.

Regards,
Dave