308 LPG mileage and tuning LPG

[juls]

Just put the wideband on the patrol. It shows a constant (ie doesnt change with revs) AFR of 15.0 to 15.2. When you back off it fluctuates to 13-14 for 1/2 a second or so.

I was surprised how constant it is, and that it doesnt change with load/revs.

The sensor was mounted in the end of the exhaust. Does anyone know if this offsets the AFR by any amount as apposed to having it mounted directly after the exhaust manifold?

Is 15.0-15.2 what I'm aiming for?

The stoichiometric AFR point of LPG is 15.5 so its a smidgen rich compared to that.

Now im getting 26-28l/100km. Is that normal for a 2 tonne patrol with a 308? Its running a 4 barrel carb with a 300A mixer and X1 regulator.

[known 2]

is that on lpg? what do u get when u run petroll???
my 308 landcruiser returns around the 30l per 100k's running a 600 4 barell carb.
with 35i tyres. so i was looking twards lpg to solve my problem.

[juls]

No petrol sorry, straight gas. 30l/100 is a lot *gulp*.

[PGS 4WD]

15.5:1 is lovely at cruise and light throttle, you want about 13.7: at Wide open throttle, under power requires more fuel or combustion temps go up and engine damage will result. Leaner is not always more economical as mixtures that lean uinder load make less power causing you to have to push the car harder all the time. If you're staright gas you'll benefit from a distributor re graph.
Generally a gas curve on a naturally aspirated engine will be about 10 degrees mechanical and 10 degrees vacuum (in crankshaft degrees) I power time the engine on the dyno normally but would suggest setting the timing around 15 degrees at idle once re-graphed, this will give performance and economy once the mixtures are set right.
Joel

[juls]

I dont have much control over the mixures. Richer or leaner is about all the adjustment there is on a 300a mixer. I would have liked to see richer mixtures under load but for some reason this doesnt happen.

Is this normal with a gas mixer?

Once I fit my electronic dizzy and eventually fit megasquirt ecu to control the ignition I will tune the timing. For now it will have to do with whatever advance I can get out of turning the dizzy. To tell the truth i havnt even put the timing light on it yet.. Ill get round to it one day

[PGS 4WD]

This is the problem with mixers, if it retains the same mixture throughout the range is usually indicates the mixer is sized wrong or the converter springing is wrong. Try richening the full load mixtures to 13.6 or so and see what the cruise mixtures are. if they also go to 13.6 I would try some heavier primary springs, also what 300 A is it a 10-20 or 50-70 series.
Something I should have thought of earlier, do you have a snorkel and if so do you have a balance line? If not you need to drill and tap the converter lid and the air intake tube to accept fittings for 1/2 inch hose, connect the two. Drill the existing atmospheric vent in the convertet. At speed the pressure rise in the intake causes the mixture to lean out.

If you want something that can be tuned properly like a petrol carby buy a Gasresearch carby, they are straight LPG unless you are EFI though.

Joel

[juls]

Cool thanks for the advice.

I dont have a snorkel but do want to fit one soon.

Ill try playing around with it a bit and let you know.

Eventually I want to get an efi setup with both gas and petrol injectors but this is more of a longer term thing, too many thing to fix up immediately before I can get to this.