Technical LPG...engine optimisation?

[190daj]

Hi,
I run a Cinquecento sporting on LPG ( well, when I fix it!) and it returns ASTONISHING equivalent MPG figures...in excess of 100 mpg !!! However, LPG is a 110 octane fuel and will therefore run at much higher compression ratios. It will also tolerate about a 10 degree advance in the ignition. This leads to improved economy/performance. I have previously used, on another car, a clever electronic box called a "dual-curve" which allowed the ignition to be mechanically advanced by 10 degrees. (This was when the car was running in LPG mode.) When switching to petrol, the box took the 10 degrees off, and the timing reverted to standard setting. I believe that this particular device is not made any more... I also thought that the cylinder head could be skimmed to increase the compression ratio, just like was the rage in the 60's...yes, I'm THAT old!!! I wonder if the ECU is programmable to alter engine timings? I would add that the car virtually NEVER runs on petrol...it starts on LPG and it would be very unusual to run out of LPG! This is an unusual thread, isn't it?...but I'll bet that it still won't stump you clever guys !!! I've been asked before as to why bother converting a car already doing ~ 45mpg on petrol?...well, the answer is to achieve phenominal economy...even better than a MOPED!...and with the looming £1 a litre price of petrol, it gets even better!!!
Thanks again,
David

 

[sei16v]

lol aint got a clue what any of that means, but if it means 100mpg then fair play to you!!! (let us know how you do it if its possible lol)

 

[Oldschool]

The ECU is programmable. If you need help pm me.

 

[smokeme]

Hi,
I run a Cinquecento sporting on LPG ( well, when I fix it!) and it returns ASTONISHING equivalent MPG figures...in excess of 100 mpg !!! However, LPG is a 110 octane fuel and will therefore run at much higher compression ratios. It will also tolerate about a 10 degree advance in the ignition. This leads to improved economy/performance. I have previously used, on another car, a clever electronic box called a "dual-curve" which allowed the ignition to be mechanically advanced by 10 degrees. (This was when the car was running in LPG mode.) When switching to petrol, the box took the 10 degrees off, and the timing reverted to standard setting. I believe that this particular device is not made any more... I also thought that the cylinder head could be skimmed to increase the compression ratio, just like was the rage in the 60's...yes, I'm THAT old!!! I wonder if the ECU is programmable to alter engine timings? I would add that the car virtually NEVER runs on petrol...it starts on LPG and it would be very unusual to run out of LPG! This is an unusual thread, isn't it?...but I'll bet that it still won't stump you clever guys !!! I've been asked before as to why bother converting a car already doing ~ 45mpg on petrol?...well, the answer is to achieve phenominal economy...even better than a MOPED!...and with the looming £1 a litre price of petrol, it gets even better!!!
Thanks again,
David

Lets see if i can answer all your questions.

Your magic box is still made, there are hundreds available but most people use it to retard timing for nitrous/boosted aplications.

You can't raise the compression ratio on these engines very much and still expect them to run on petrol because it will detonate. Another thing is if the car is never to run on petrol the rubber seals will deteorate and cause leaks over time.

The stock ecu can be remapped to alter timing but it won't control the LPG injectors anyway, probably will throw a light since you have to disconect the fuel injection part (pump, injectors etc).

The best method is to do the same i did on my Calibra (if you had a turbo car) and simply increase boost when running LPG, this way i get roughly the same power and CHEAPER running. Notice i said cheaper not better since it will use more LPG then the petrol equivelent, it will just be cheaper to refill.

One thing you should know is that every car i've driven so far on LPG was more slugish then when running on petrol.

 

[chaos]

One thing you should know is that every car i've driven so far on LPG was more slugish then when running on petrol.

Yeah LPG engines will put out less bhp than the equivalent petrol engine. Its the same when you convert a leaded engine to unleaded, but that's due to the lower octane rating of unleaded compared to 4 star.

 

[paul_treg]

Hi,
Why don't the gas companies up the octane rating of the LPG by adding a small quantity of Oxygen or Nitrous Oxide....

Thanks
Paul T

 

[Surrey Sporting]

We had a 1.8 vectra at work that had LPG. It was 'slightly' slower / more sluggish, but it really wasn't that noticeable...

Hats off to you for converting the Sporting - I'd say 100mpg from a four seater car that does 100 + mph is a good deal !

 

[190daj]

Great! ....a good response already! Well, the car does well in EXCESS of 100 mpg! The "Dual-curve" website has told me that they no longer make the model that I've still got, but which is faulty!...only units for certain U.S. cars...Does anyone know of a second-hand dual curve box, please? I've personally converted cars to LPG since the 70's and currently run two MERCS and this Sporting on this fuel. Also, the Dutch GSA lpg kit has its own ECU, so it might create problems trying to remap the FIAT ECU? Now, I said that the car doesn't need to EVER run on petrol, and I've got a spare cylinder head from my 1148cc sporting ( oh, is it compatible with the 1242cc Punto engine block?) so could I experiment with getting it skimmed to increase the compression ratio? How do I determine how much to skim off to increase the compression ratio enough to handle the higher octane ratio of LPG?
Thanks for all the interest!....David

 

[smokeme]

Great! ....a good response already! Well, the car does well in EXCESS of 100 mpg! The "Dual-curve" website has told me that they no longer make the model that I've still got, but which is faulty!...only units for certain U.S. cars...Does anyone know of a second-hand dual curve box, please? I've personally converted cars to LPG since the 70's and currently run two MERCS and this Sporting on this fuel. Also, the Dutch GSA lpg kit has its own ECU, so it might create problems trying to remap the FIAT ECU? Now, I said that the car doesn't need to EVER run on petrol, and I've got a spare cylinder head from my 1148cc sporting ( oh, is it compatible with the 1242cc Punto engine block?) so could I experiment with getting it skimmed to increase the compression ratio? How do I determine how much to skim off to increase the compression ratio enough to handle the higher octane ratio of LPG?
Thanks for all the interest!....David

If the stock sensors remain conected to the stock ecu it should work the timing with a remap. I think you mean 1108, and yes it will fit the 1242 Punto block (it's the same head as the Punto 60). In my experience LPG only contains slighly under 110octane which detonates at around 12-13: compression ratio. To achieve that you need to shave 1mm off the head and use the 1.8mm head gasket, this gives 11:1 CR (there are 1mm gaskets too, but makes it 12.33:1)


BTW nitrous only adds oxygen to the combustion and in no way does it increase octane rating

 

[paul_treg]

BTW nitrous only adds oxygen to the combustion and in no way does it increase octane rating

Hi,
Yeah but it makes a bigger bang......

Thanks
Paul T