you cant tune the 2 fuels to optimam effieciency,so the mech wouldve tuned the car to the fuel you are most likely to use more often ie lpg

An octane close to 100 for LPG is current and if that's the case and you use regular unleaded, you'll destroy your engine very quickly.

I'd dare say a mechanic has tuned a vehicle for the lowest common denominator. I would hazard a guess that over 99% of tunes will be for regular unleaded since this will get used occasionally.

Thats part of the reason I commonly get around 470-500km of suburban driving out of 62-ish litres of LPG in my EL fairmont, I've advanced the timing so close to a dangerous amount because I only run on LPG and thats the only fuel I thrash the engine on. Once a week I run it on petrol for a minute or two as I'm on cruise control in a long straight and level 80km/h zone to keep engine load under 20 percent. Even with Ultimate 98ron petrol, it still pings quite loudly under wide open throttle.

I would guess that if I let my mum drive my car on petrol (apart from burning the clutch out in a few weeks) that the engine would be forced to suffer a serious case of rebuilditis.

LPG contains less energy per litre, so your LPG fuelld car needs to consume more fuel to create the same amount of energy compared to petrol.

Also note that the intake ability of most LPG cars is reduced by about 20% due to the LPG and Air being mixed at the throttle body rather than just before the intake port.

Thats irrelevant unless you have an aftermarket computer, or carby.. theres no tuning which can be done on EFI cars.

Oh. Instead of tuning I'll just call it altering base spark timing for the purpose of achieving maximum power and fuel economy for a given fuel.

Might go and look up the definition of tuning in a dictionary.

Is that why the dedicated cars have the 55mm restrictor on the 70mm throttle body????

That should be set as per manufactures specs.. your ECU relies on the base timing to be set per spec to ensure correct ign timing. Thats like eBay tuning.. putting a resister on your IAT to gain 40KW

The max torque isnt made by cranking your dizzy as far as it goes before the enigne pings and then backing it off 2*

Well I have no experience in tuning Ford ECU's or how its done or anything related to them.

I do have experience tuning (chipped) factory RB20DET ECU's for Nissan's and some aftermarket ECU's and very much most of the time more timing for a static fuel and boost map equals more power. Once you get into severe detonation the power graph will back off.

On LPG the dyno figure for my car went up by 11rwkw to 129rwkw with my tuni.... ahem, "distributor adjustment". The maximum I could achieve on 98ron was 130rwkw with a little advance but at that point LPG was sitting on 122rwkw.

Knowing what my daily fuel is, I chose to leave it on the most advanced setting which gave me most power, one degree behind the point where the knock sensor started talking quite loudly however still inaudiable.

I've played with it a lot, in my quest for maximum economy I've probably wasted more fuel on the dyno than I'll save in 5,000km of driving


edit -
Remember, I'm not tuning for emissions which often dictates a slightly non optimal tune for power and economy. I dont have a 3 gas emissions analyzer and I bet NOx emissions are possibly higher since the advanced timing however other emissions would be lower.