Alternative Fuels

Hello,

Due to outstanding high LPG prices, drivers and LPG tuners searches new approachs. Lately we seen cars tuned to 18.0 afr at 3000 rpm and also they had smaller mixer intake holes.

Drivers claims very good millage and good enough driveability.

Is there any bad consequences using cars at 18.0 afr ?

And is there any good practices about the tuning cars at very lean.

My Best Regards...

I'm interested in the answer to this from other more knowledgeable technicians as well but will just post my thoughts.

At cruise conditions I can set my dinosaur EFI (meaning old EFI technology from the mid to late 1980s) up to run 17 to 1 on Unleaded petrol and get good economy and good cruise power and drivability. As soon as the TPS or other sensors detect a change it immediately reverts back to 14.7 to 1 or richer depending on load etc. LPG runs leaner anyway so I would assume 18 to 1 is not out of the question (if it is on an equivalent setup). The issue I would see is that mixers are the same as carbies in that they are required to fit so many different engines and there is limited tuning range on old technology systems. You also need to remember that petrol starts damaging engines when run too lean but LPG damages engines when run too rich.

My daily sees 18+:1 AFR regularly.
As long as it's not under power you'll be ok.

I have messed with lean AFRs and timing, and others have to in these forums way back.
Modern petrol engine technology is getting so petrol can be burnt very lean at cruise ....
With lpg once I get over around mid to high 16s theres no advantage in economy cruise get over low to mid 17s and economy drops off.. even with adjusting timing.
Have had LPG way out to 18 low 19s on cruise.. no heat issues runs ok, so long as richens up with load.

in earlier days of fiddling with LPG we had a customer who had a better background than we did in engineering - he was working on a drive system for a big motor company in a very cool work environment hundreds of miles away from the factory. When reviving his old LPG system on a UK V8, to get it sorted and running, we later found it was running 19:1 AFR on cruise. he did not want it changed , was happy with the way it was - liked his economy more than emission laws I suspect. Never got to see how it lasted at those rates - relationship soured after some tiny issue