More poke from my V8 on LPG

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Probably worth mentioning that the Bosch Motronic does have advance variation built in, it has twin knock detectors to allow it to run high advance where needed.

Peter
 
an open loop system can eaisely be changed to closed loop by using a VIP 100 unit from Tinley Tec.
you get better fuel consumption and the unit displays the fuel mix so it can be set up by the home user very eaisely.
 
Open loop is where the control loop is not continuous, ie the mixture (input) is not continuously changed by feedback from the exhaust Lambdas (output)

Closed loop is a continuously running loop where feedback from the output is used to vary the mixture at the input.

If you watch the Lambda voltages in real time on a Thor engine you will see them toggling up and down as they respond to mixture control from the ECU. As there is a time delay between sensor, ECU and injectors, the process is a continuously variable voltage that goes up and down within a limited range or window. Hawkeye or and OBDII reader can show this, and it is one of the clearest signs that the control is working properly.

Peter
 
OK, thanks for the explaination. My system is much more primitive. Basically a vaporiser and two mixer rings.
Still no chance to check the timing i'm afraid as the car is away having its rear crossmember replaced.
There is a lot of information being offered on LPG here and i realise that i have a lot to learn, but i'm grateful for the chance to learn.
I suppose i'm looking for the perfect balance between MPG and power but with a small budget.
Currently getting about 13mpg on gas which is acceptable but any improvement would be welcome.
 
That's why multipoint is so much better, the mixture is better distributed between the cylinders and you'd have closed loop control.

It's not impossible to get mixers working OK, but it's all down to setup and tweaking as you go along.

The individual gas nozzles on our 4.0 are just above the inlet manifold to head joint, but the pipes to the gas valve blocks are quite long, so there's a bit of latency in the throttle response, not much you can do about that unless you can get the valves individually mounted close the the ports.

The other interesting thing that it does is burp on the overrun when there is a bit of gas in the pipes and the lost spark ignition fires it on a cylinder that's on the exhaust stroke.

It's an interesting subject and although it looks very complex, it is quite simple as long as you have the system working. They can be a nightmare when they go wrong!

Peter
 
zen said:
soooooooooooooooo disagree...i have 10 degree more timing at 0 bar..and 6 at .6 bar..

now those who have not tried multipoint or indeed direct liquid injection, should in my oppion keep shut...

and to those who run same timing on petrol and gas REALLY ought to try advancing on gas....the difference is large..ie 1 sec off 0-60 or 2-3 mpg..

mulipoint..no back fires..precise fueling..better safty..more power..more mpg..WHY you think mulipoint was developed??

JUST my oppion, though its correct..(lol)
Click to expand...

I agree ...On carbs with two gas rings you definitely do need more advance when on gas

My later 3.9 injection rangie on single point gas also went better with more advance on gas.

And I never EVER had a backfire when on gas with either vehicle, those that do have a problem with settings:)
 
johndregg said:
Another newbie question: standard RV8 timing? And what should I aim for on gas?
Click to expand...

On petrol advance it till it pinks under load then back it off a bit till it doesn't. No point in numbers as every engine wears different and has different needs. Engine needs as much advance as it can get without pinking
Mark dizzy and body with tipex so you know where petrol setting is.

Advance more for gas till it runs best (about 1/4 inch on body) and mark again so as you can move between the two when needed.
 
To advance, you turn the distributor body in the opposite direction of rotation to the rotor arm, to retard you turn it in the same direction as the rotor arm.

Peter
 
listerdiesel said:
The individual gas nozzles on our 4.0 are just above the inlet manifold to head joint, but the pipes to the gas valve blocks are quite long, so there's a bit of latency in the throttle response, not much you can do about that unless you can get the valves individually mounted close the the ports.


Peter
Click to expand...

hi peter..you can get around that...but it means megasquirt or similar..it gives you the option of injection timing in regard to spark..ie on gas you can adjust when injected in relation to rpm and stroke..thus longer the gas run from valve(engine) to valve(lpg) the more advanced you make gas injection time..
i love my megasquirt...lpg works better than petrol, and i run 99 octane, better mpg,better power (due to many degree more advance)and no pinking!!
and you can adjust gas law to take into account lpg temp etc, so even on mulipoint it starts mid winter on gas..the latest king ecu i use (lpg) just switches the injectors etc, all settings are set to 1:1, i let the ms ecu do the maps..
 
I speak through experience on this on .
twin SU at conversion was crap carbs cont out of balance and no poke .
customer came back two months later with a four barrel carb and manifold , i said bit extreame but wtf , it wasnt my money .

A twin choke webber off a three liter capri would have done the job and a modified manifold.

anyway we stuck a mixer on top the carb in the form of a moving plate mixer / air filter and F**k did it go some .

No more imbalance problems or tuning issues .

option two is a stand alone injection system early romanos were self set up and no injector signals (research needed on this one now )
rpi engineering do a moving plate mixer as will mint lpg
 
I was wondering - what air intake are you running?

On my 101, ( running a hc 3.5, with su's and a mixer on each carb) I couldn't get the mix rich enough, and it would run out of puff at higher revs.

Turns out that the air intake system was very efficient, and didn't present enough of a depression to the LPG mixer.
So we introduced a restrictor plate into the air intake behind the massive 101 air filter.

It didn't need much of a restriction at all to bring the fuelling back into line.

I always run with ignition set to LPG settings, and go very lightly on the throttle if running petrol.

Never really run petrol - too expensive!

Oh, and I suppose someone's mentioned that LPG will expose any ignition system weakness.....
 
listerdiesel said:
Probably worth mentioning that the Bosch Motronic does have advance variation built in, it has twin knock detectors to allow it to run high advance where needed.

Peter
Click to expand...

From experience, nearly all petrol ecu's have a hard coded limit set that stops the ignition auto- advancing far enough to make full use of the LPG's octane rating. Yes, it will advance a bit, but in order To make full use of this, the ecu needs to have this limit tweaked.

Some manufacturers ecu's are designed to run Bioethanol, and have two ignition advance curves - one for each fuel. I am trying to exploit this on my Saab 9-5. By wiring the Bioethanol sensor input to the LPG "active" line, and enabling greater ignition advance on LPG... We'll see how it goes...
 
Sorry - just re-read OP.
It's a single point electronic LPG setup on a carb engine?

Never actually comment across one of those!
I was under the impression that you had to have EFI to have a single point LPG...
 
captainbeaky said:
From experience, nearly all petrol ecu's have a hard coded limit set that stops the ignition auto- advancing far enough to make full use of the LPG's octane rating. Yes, it will advance a bit, but in order To make full use of this, the ecu needs to have this limit tweaked.
Click to expand...

It will advance it to the point of knocking when it's cold, that's far enough.

Peter
 
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