Timing map for LPG

[andrew_mx83]

So i have got my dirty little mits on a Hand Controller for my jaycar programmable ignition box (thanks heaps to richzx) to run the spark side of things on my straight LPG setup.

i have never done an ignition map before but im told that it is pretty simple for LPG. the box supports 2 maps (11x11) so i will have one for everyday and one for a bit of extra oomph at the expense of engine life.

the engine is a mild 7m-ge running 10.8:1 comp and will be fed by an impco 425 mixer. all toyota electronics & ecu are going. intake cam is retarded 3 deg so the motor comes on cam around 3000-3500 rpm and just keeps pulling. car is 5 speed with a lightened flywheel & button clutch and likes to rev.

i know i need to run low advance at startup to make cranking easier and would also like to have bugger all on overrun so it will keep its nice burble and maybe develop a bit of snap crackle and pop

by what rpm should it be running max advance? from what ive been told on LPG i have to bring the advance on fast and strong and then have the curve fairly flat from there to redline or even drop a little right at the pointy end of the tacho.

edit: a bit easier to read and revised


here are 2 really rough base maps i came up with:

DAILY
0 700 1400 2100 2800 3500 4200 4900 5600 6300 7000 7700
L1 5 5 5 5 5 5 5 5 5 5 5 5
L2 5 5 25 30 35 35 35 35 35 35 33 31
L3 5 5 23 28 33 33 33 33 33 33 31 29
L4 5 5 21 26 31 31 31 31 31 31 29 27
L5 5 5 19 24 29 29 29 29 29 29 27 25
L6 5 5 17 22 27 27 27 27 27 27 25 23
L7 5 5 16 21 26 26 26 26 26 26 24 22
L8 5 5 15 20 25 25 25 25 25 25 23 21
L9 5 5 14 19 24 24 24 24 24 24 22 20
L10 5 5 13 18 23 23 23 23 23 23 21 19
L11 5 5 12 17 22 22 22 22 22 22 20 18

POWER
0 700 1400 2100 2800 3500 4200 4900 5600 6300 7000 7700
L1 5 5 5 5 5 5 5 5 5 5 5 5
L2 5 5 35 40 45 50 50 50 50 50 50 45
L3 5 5 34 39 44 49 49 49 49 49 49 44
L4 5 5 33 38 43 48 48 48 48 48 48 43
L5 5 5 32 37 42 47 47 47 47 47 47 42
L6 5 5 31 36 41 46 46 46 46 46 46 41
L7 5 5 30 35 40 45 45 45 45 45 45 40
L8 5 5 29 34 39 44 44 44 44 44 44 39
L9 5 5 28 33 38 43 43 43 43 43 43 38
L10 5 5 27 32 37 42 42 42 42 42 42 37
L11 5 5 26 31 36 41 41 41 41 41 41 36


how far off being right does that look?? as i said i have never done one of these before

[amichie]

Maybe you can find out the ignition maps used in FORD and HOLDEN factory fitted LPG systems. That would make a good starting point.

[oldcorollas]

http://www.acl.com.au/web/acl00056.n...e?OpenDocument
?

maybe think of it as a timing map for "supagas" or a timing map for "shit gas"

[web]

That's a ten year old article with surprising content : how does LPG know the engine is operating at high speed, making it burn faster? I mean, it's ignited and then it burns at a certain speed... depending on pressure and temperature perhaps, but engine speed?? And enough to require radically different timing too??

Also, in 6 years of driving various LPG vehicles on stock petrol timing maps, I've never ever heard high rpm det... sales pitch for a timing box?

Googling around I can't find any confirmation - every other site in the world suggesting advance only, if anything, except for one copy of said article.

Even a competing timing box sellers tell a different story: http://www.iwemalpg.com/TAP.htm or http://www.v8engines.com/faq-lpg-ign.htm

My understanding is retarding timing will burn your valves very fast on LPG. So I definitely wouldn't follow that advice without further research.

I guess it comes down to dyno tuning being the only proper way, once again.

[andrew_mx83]

i have been trying to find a map from a factory gas ba falcon....i think that would show me exactly what i need....... but not having much luck with the internets.

i will be running Supagas 100% propane all the time its just a matter of not stressing the engine on a daily basis...i dont fang it all that often. its got the option to have a switch so i may as well have the best of both worlds.

the hand controller arrived today (thanks heaps to richzx) so i will probably jsut program in the numbers above and see how it goes. from the reading i have done they dont look too bad.
but then there is a LOT of misinformation out there :S

[oldcorollas]

That's a ten year old article with surprising content : how does LPG know the engine is operating at high speed, making it burn faster? I mean, it's ignited and then it burns at a certain speed... depending on pressure and temperature perhaps, but engine speed?? And enough to require radically different timing too??

Also, in 6 years of driving various LPG vehicles on stock petrol timing maps, I've never ever heard high rpm det... sales pitch for a timing box?

Googling around I can't find any confirmation - every other site in the world suggesting advance only, if anything, except for one copy of said article.

Even a competing timing box sellers tell a different story: http://www.iwemalpg.com/TAP.htm or http://www.v8engines.com/faq-lpg-ign.htm

My understanding is retarding timing will burn your valves very fast on LPG. So I definitely wouldn't follow that advice without further research.

I guess it comes down to dyno tuning being the only proper way, once again.

hmm, a friend of mine who has done a fair bit of development on turbo gas systems (on old clunker ford motors ) iirc thinks the same...
which do think is better.. rich or lean with LPG?

[andrew_mx83]

lean with LPG will usually run hotter and burn valve seats
not sure about if it runs rich......i read somewhere that it will run hotter but cant see how this would work.

do the impco systems have any sort of acceleration enrichment? do you need it on gas?

[web]

My experience with fuel mapping LPG is that it doesn't need nearly as much cold enrichment or power enrichment as petrol. I guess that comes down to it mixing well with air in just about any circumstances, while petrol has a bit more trouble with that. Not 100% sure about accel, it's been a while. I do know many venturi mixer type LPG systems run fine without any form of accel enrichment at all, but that doesn't mean they wouldn't run slightly better still if they did have it. It does suggest LPG would need less accel enrichment, too.

When googling yesterday I also found a page of some Subaru dude running LPG, and finding he could advance 10 degrees across the board without pinging, relative to the old petrol map. But anything over 4 degrees lost power, so he settled on 4 degrees advance. Shame I can't find that link anymore today...

So much misinformation going around however - and many people spreading knowledge as fact that they "read somewhere", only a full dyno tune session will probably tell for sure. Which I'll probably end up doing sooner or later - currently I just lack an LPG car that I can alter the timing of.

Until I see evidence or a good explanation, I'm not yet ready to believe a combustible LPG mixture somehow "knows" engine speed, and decides to burn faster than petrol at high rpm, but slower at low rpm.

[oldcorollas]

maybe it is due to the heating during compression..
LPG temp, being gas, will rise at same rate as the air it is mixed with.
with petrol, if temp of air rises, some of fuel is already vapour, so will increase similar
some of it is liquid still, and will increase temp less? (check Cp for fuel?)
but some will change from liquid to gas = sucking in heat energy and reducing temp.

so.. temp of compressed mixture is higher for LPG.. maybe...
that combined with the petrol still being in droplets which have a slow burn rate, might mean LPG needs less advance than petrol, due to a faster burn rate..

as for more advance at low rpm.... i'm fresh out of ideas and time

edit: i do remember my mate saying LPG was far less picky about the actual AFR than when he was using petrol.... pity he is not online so i can pick his brain more

[web]

LPG not being picky is true...mixture can be way off and still seemingly run fine. That's why very primitive conversions involving ring mixers can work so well, although I wouldn't touch them on a performance car.

Timing... well... a proper dyno session someday should tell.

The problem with LPG is, too many ppl think installing a completely different fuel system is like bolting on a new set of foglights - nobody ever seems to propely map an LPG car on the dyno.

[Grega]

The problem with LPG is, too many ppl think installing a completely different fuel system is like bolting on a new set of foglights - nobody ever seems to propely map an LPG car on the dyno.

how true with LPG
good example of this is look at some of the results with this new ethanol stuff.

OK, i know its not a toyota
I had a 202 running straight LPG thru a gas research S350 mixer and aussie B2 convertor.
my dizzy as it was, was all in by ~2000rpm 32 degrees. we threw tonnes of timing at it ; and ; it went really well. it was effectively the same dizzy re-curve as what they did for the holden 202s running avgas in the HQ series if that helps.

once the GRA S350 was setup with the metering jets for progression the thing flew. it made 88rwkw on BBQ fuel (not bad for a 202 considering the stockies would be lucky to make half that on a good day)

andrew

i will be running Supagas 100% propane all the time

tell me how you do this? PM me if you want. and yes, the LPG fuel we get these days is more butane than propane making it utter shit.

[andrew_mx83]

maybe it is due to the heating during compression..
LPG temp, being gas, will rise at same rate as the air it is mixed with.
with petrol, if temp of air rises, some of fuel is already vapour, so will increase similar
some of it is liquid still, and will increase temp less? (check Cp for fuel?)
but some will change from liquid to gas = sucking in heat energy and reducing temp.

so.. temp of compressed mixture is higher for LPG.. maybe...
that combined with the petrol still being in droplets which have a slow burn rate, might mean LPG needs less advance than petrol, due to a faster burn rate..

as for more advance at low rpm.... i'm fresh out of ideas and time

edit: i do remember my mate saying LPG was far less picky about the actual AFR than when he was using petrol.... pity he is not online so i can pick his brain more

this is correct. the Bosch Automotive Handbook (maybe more "fact" than the internet) shows LPG burns 45% slower @ atmospheric pressure and a certain temp. as temp and pressure rise the mixture will burn quicker so that seems to agree with the idea of bringing all the advance in nice and quick cos it needs it most down low.

im going to program the above values in (maybe 1deg on load 1) and hope to have in running next week to see how it goes. a dyno tune may well be needed down the track but i have to get it running first.

its good to know the mixtures dont have to be perfect though. apparently stoic for LPG is 15.5:1 so i will try and get some numbers off the o2 sensor and see how close i can get it.

GREGA -do you have a Supagas out there in Hoppers?? i know there is a couple out west but cant remember exactly where. some (not all) of the stores have filling stations for cars and you have the choice of "autogas" (50/50) or 100% propane. i used this whenever possible in my hilux and got more power/torque and 10-15% better economy.
the other good thing is they only set their price ONCE A MONTH so no more of this fuel week cycle bullshit. i find the autogas is usually a bit cheaper than servos and they add a couple of cents for the propane but it is well worth it. just remember they are only open business hours.

if this damn kitten walks on my laptop and deletes everything ive written once more im gonna crack it lol

[Grega]

lol @ kitten
they are good like that
i have a full grown cat that does it

yeah - theres a supagas in brooklyn where i get my argon from. i'll ask as i'm due for more welding gas. thanks dude

[oldcorollas]

where do your taxis fill up?

[Grega]

where its cheap stu