LPG Discussion Forum

i dont mean the LPG ECU, but the actual engine ECU. I gather the LPG ECU gets its inputs from the standard engine ECU injector pulse signal?

On my old evo I tuned the thing to run at leaner AFRs than stock during certain load/RPM conditions, which i would compliment with adjusted ignition timing to adjust the ignition point in the compresison cycle. While i took care around things like cylinder temps etc, the first thing that would manifest when being a bit too lean is the knock. Stick some higher octane fuel in there and I could go leaner, so I ended up having two maps on my ECU - one stock map for 'normal' fuel and one 'lean' map for when I was running 100 octane. Naturally, I got more power and more MPG when using the lean map.

So reading into LPG a bit more, the octane is comparable to alco fuels and other high octane fules (110 IIRC) so whats to stop me tuning my engine ECU to run on a map which, while being suicidal on petrol, would give me better use of the LPG? Something like a 16.5 AFR at low load cruise and something round 13 AFR at heavy load (aka heavy foot). I guess all i can think of is that if the system switches back to petrol its going to knock a lot, but as I will be running mainly on LPG I can compensate for this by ensuring any petrol i have in the tank has MTE or some other similar additive. Id also imagine that at idle and low load ill need to add timing so i dont burn out the exhaust valves, wheres i can pull this at higher load. My compression ratio is already pretty high (10) so that helps things too.

Am i completely barking mad with this line of thought?

simonp wrote:Am i completely barking mad with this line of thought?

Not at all, but it's all at your own risk.

These are avenues not available to "ordinary" users stuck with a car's standard closed-loop system and ignition map. If you're going to the trouble of remapping all that, you might as well fit a dual mapped ECU and optimise for both fuels?

This kind of thing makes sense for maximising performance, but from an economy viewpoint you are getting into the law of diminishing returns ... have to put quite a bit of effort into beating a modern eurobox cars economy by any significant amount. If you're starting from an EVO, obviously it won't be factory setup for economy, so there might be something to gain. But then why have an EVO ...

rossko wrote:

simonp wrote:Am i completely barking mad with this line of thought?

Not at all, but it's all at your own risk.

These are avenues not available to "ordinary" users stuck with a car's standard closed-loop system and ignition map. If you're going to the trouble of remapping all that, you might as well fit a dual mapped ECU and optimise for both fuels?

This kind of thing makes sense for maximising performance, but from an economy viewpoint you are getting into the law of diminishing returns ... have to put quite a bit of effort into beating a modern eurobox cars economy by any significant amount. If you're starting from an EVO, obviously it won't be factory setup for economy, so there might be something to gain. But then why have an EVO ...

Good to know, glad im not mad and the more i read about LPg the more sense it makes so things are looking up. The Evo is long gone sadly, had it years ago when i was in my younger boy racer era. Im now in my older, flat cap, pipe and slippers era so its a 5l v8 Merc M class. Im not to bothered about perf gains, its already doing 0-68 in under 7 seconds its more maximising the cruise MPg when on gas (i do 360 miles per week round trip london and back, hence looking into LPG)

Thanks for the feedback, i really appreciate it (esp from someone with so much experience!)

*ninja edit* didnt reaslie there was a thread right next to this one about going leaner. interesting to hear that it impacted MPG negativley

simonp wrote:Im now in my older, flat cap, pipe and slippers era so its a 5l v8 Merc M class.

Surely it should be a Rover 75 then?

Gilbertd wrote:Surely it should be a Rover 75 then?

Not quite there yet

Some of the aussies seem to be picking up on this
http://modifiedmagna.com/viewtopic.php?t=710&p=8371

esterday had my car tuned by Dave (merlin) for LPG only, he advanced spark to take advantage of high lpg octane from loads 70% and higher. So basically car will not be drivable at WOT or high load on petrol (unless i want to blow my piston). Results we very surprising given previous tune was for 98 octane petrol. LPG outperformed through out the range with most gains in the mod to top end power. You can see how motor desperately needs new cams (look at torque curve, past 5000 it drops like crazy). Dave thinks that it can be taken further but without knock he did not want to advance it more (hence next project to get one working from Diamante), he thinks another 3 degrees are possible, which would mean another 25 horse power at the wheels. Blue like 98 octane tune red line lpg. This was done via Evoscan, so the actual power number seems quite low (on every dyno ive been so far i had higher figures), but what this demonstrates is the difference between two fuels.

I feel sorry for this guy if hes under WOT (or even over 70 load) and his tank runs out or a problem causes and underpressure - back to petrol and kablam. Though I would have thought under forced induction with LPG, things would be getting rather hot in there, without petrols evaportive effects etc - so maybe timing should be pulled up top, not added. I really hope this tuner doesnt add timing and then try to richen out the mixture in the stock ECU while on LPG in order to counter knock; bit of a blowtorchy type effect.

I know of another forced induction guy running LPG on open loop stock ECU from idle upwards - he uses lambda emulation and +5 timing to get the fuel economy up by running AFRs around 16.8/17 at cruise, seems to give him a nice bonus in mpg.