LPG performance = petrol !

[M D E]

Just had my first 1000 mile service on my C70 T5 (is actual covered 3000 miles) since the conversion due to it being so cheap to run....

I told the conversion company I could tell the difference on LPG as the power was down running on gas, flicking over the petrol gave me my T5 performance back

The result - they re-tuned giving me the same performance on LPG as petrol. I was supprised as I heard that LPG was allways going to give less power .... But not anymore. I did have the larger fuel injectors fitted to cope with the T5 engine .... So now £18 is 180 miles with full performance.

[classicswede]

Yep, should not have gone back to you without it driving 100% on LPG

At least they did sort it when you went back

[foggyjames]

My understanding is that as long as it's tuned right, there should be no notable reduction in performance when running on gas, especially a multi-point kit. If the car has an "advance until ping" style ignition system, it may even make more power, bearing in mind LPG's octane rating. I heard of an early 960 doing just this.

cheers

James

[classicswede]

James on the nail with that one. Subaru's are one of those that make mush more power on LPG - partly octane and partly fuel mixture.

[davew]

LPG will make slightly less power. Its not to do with the octain its the calorific value.

[classicswede]

The calorific value is lower for LPG - that is why you use a little more LPG than petrol.

Turbo engines can be able to make use of the octane and produce a little extra power.

[Clan]

Originally Posted by classicswede

The calorific value is lower for LPG - that is why you use a little more LPG than petrol.

Turbo engines can be able to make use of the octane and produce a little extra power.

Then you drain the tank in no time with the huge quantities of LPG consumed , much like E85 flexi fuel ..

[classicswede]

Not realy. The quoted amount is upto 20% extra fuel used. With modern LPG injection systems it is more like 5% extra fuel used for the same milage. In odd cases certain cars get better MPG on LPG than they do on petrol but only on certain cars with poorly designed petrol systems (VW air cooled).

When you consider the price difference even with the 20% LPG needed you are still basicaly halving you fuel bill.

I don't know how much petrol cost these days (just over £1/ltr?) as it must be over 6 months since I last paid for some of that stuff but LPg is costing me 47p per ltr at the local filling station

[foggyjames]

The stoichiometric ratio for petrol is 14.7:1 (air to fuel) and 14.0:1 for LPG, if memory serves correctly. *Deliver the fuel correctly* and there's not a lot in it. My understanding is that the older systems simply don't meter the fuel accurately at all, and are responsible for the bad image that LPG has. Modern multi-point systems pretty much solve the problems.

Well...that's what I'm hoping, anyway. I've recently picked up a multi-point system for my S70, so I'll be interested to see how I get on!

cheers

James

[Clan]

In 1979 - 1985 when i was doing official Volvo LPG conversions it was the case that the power was down 10% and volume used about 15% more These were simple systems though with a venturi which the air passed through drawing in LPG before going through the carb . they worked well and were economic before the tax killed it off in the late 1980's . The Factory system on the S/V40 and S60 etc are a bit more sophisticated in that there is a metering unit which is linked to the ECU to let more or less gas in depending on demand . The latest systems which have 4 or 5 injectors should be able to control it much more precisely getting the best out of the LPG ..