I have been of the understanding that a Dual Fuel setup (non-injected) has an ignition timing compromise - to run both fuels, the LPG gets a late spark while petrol gets an early spark. This is because LPG burns slower, so it requires an earlier spark to effectively use the power stroke.

Now, I have read how PULP can utilize advanced timing.

Taking my TS Auto 2.6L EFI engine as an example, it specifies 13 deg +/- 2 deg BTDC, for both ULP and PULP.

Now, I aim to get this baby converted to a venturi-style dual-fuel that will start on petrol by default, then automatically flick itself over to LPG. I can get this for $2,600, then get the $2k back. For $600 out-of-pocket, it wil pay itself off within 6 months at today's fuel prices.

However, I aim to use 98 RON petrol, so the timing can be set a little more advanced toward LPG's optimum, without any pinging probs.

Does anyone happen to know:


What the ideal timing for LPG in this kind of engine?
What timing can one get away with on PULP, if not intending to use ULP?
In a PULP/LPG setup, what would be the best timing? Note: Car does not tow


Eagerly awaiting your thoughts...:)

I keep the falcon about 2 degrees advanced.

I removed what I put before as every one has a different opinion or test results
This guy has some good things to say.

http://holdenpaedia.oldholden.com/index.php/LPG



Timing Advance Processors are what those buggers are called that advance your timing for you LPG and let run on normal for petrol, or get a piggy back.

I removed what I put before as every one has a different opinion or test results
This guy has some good things to say.

http://holdenpaedia.oldholden.com/index.php/LPG



Timing Advance Processors are what those buggers are called that advance your timing for you LPG and let run on normal for petrol, or get a piggy back.
Thanks for the link. Yeah - perhaps a better way to compare LPG combustion would be that it ignites faster and burns longer, so an earlier (more advanced) spark will allow the power stroke to better use its energy. Reading that info shows that for the Holden red engine, optimum LPG timing would be 6 degrees more advanced than optimum petrol timing.

I'll have to check whether the LPG fitter I have pegged would supply & fit one of those TAPs.

Regarding the restrictive nature of the mixer ring, I'm wondering whether this could be compensated for, using a less-lestrictive air filter. If so, would I have to go to the expense of a K&N, or are there other filters worth considering, or layouts eg open-element?

There was a bit about it being harder to ignite, so some have open their plugs up a further 0.1 mm but NGK say reduce it
http://www.ngkspark.com.au/pages/bulletins/T92-1.htm
and some say change the type of plug from platinum to iridium
http://cracker.com.au/cars-bikes-boating-forums-forum/cars-forum/lpg-on-pajero-backfiring/138338/thread.htm?search=1
More support for Iridium
http://www2.pajeroclub.com.au/forum/showthread.php?p=18381

As for the Advance timing, there are some schools of thought that you may need to reduce the amount of vaccuum advance if you do advance the timing. =This sounds like something only a dyno tune could sort out. The Increase RPM to timing advance in our cars was designed for petrol and is not perfectly suited to the characteristics of gas, and every choice you have will have some type of compromise.

Its a very interesting subject though, and I am learning heaps.

I had a quick word with an installer, and brought up the topic of distributor settings and any advantages of using PULP as the ptrol in the duel fuel setup.

He responded that the distributor does not get touched, and the petrol type will make no difference to LPG performance.

Bearing in mind, the conversion is to be for a TS sedan with the 2.6 MPI engine, does this sound correct, anyone?

Its quite true that distributor wont get touched etc, as they keep it running on petrol like normal. However, like you have realised this is not optimal.

I would recommend doing as you said, advancing the timing yourself, and just making sure you always use 95 or even 98 ron. Keep in mind LPG is about 100ron I think. I think I am going to try the same thing on my car, but have no clue on what timing to use. I would probably just keep advancing it slowly until it starts pinging, then retard it back a few degrees.

Considering you will be running on gas most of the time the premium fuel wont matter much. Should give the car a tad more power, and probably make it a bit more responsive etc.

So although the guy is right, petrol type will make no difference to LPG performance, but you can advance the timing yourself to get more out of LPG. And to prevent pinging at this advanced timing, you will need to use a high ron petrol.

Hope that makes sense :doubt:

Good luck! and let us know how you go, my car gets converted with injection on the 9th september :)

Ollie

With all my research i did when building the dedicated 308ci V8 for my HG premier,the conclusion was that LPG requires a heap of intial or "static timing" (dependent on RON and compression etc of course being the limiting factor) and less total at higher revs,We also did away with vacuum advanc eon the dizzy altogether,On my paticular engine,i was running about 20 degrees static and about 10 mechanical for a toal of about 30 degress,Whereas petrol likesl ess inital and more advance higher up,this is where the compromise has to be made,the only advantage would be a few degrees more initial on PULP for a slight gain in botom end

Steve

as for the plugs in gas cars guys, if its so hard to ignite go bac to coppers and stay away from platinums and iridiums for 2 good reasons, without upgrading your ignition system, coppers will always produce the strongest spark to an equivelant iridium or platinum as copper has far less resistance then the other 2 materials causing an easier flash-over between the electrode and prong and 2ndly coppers wont foul as easily since the massive reduction in carbon residue in the exhaust gas when using lpg, things just wont foul and gunk up, you'll actually be able to use a copper plug will it wears out, which is vastly longer then before it fouls on a petrol engine (obviously not like a platinum)

I thought Iridium had less resistance than copper, or is it only less resistance than platinum???

Ollie

less resistance than platinum and better durability than copper (by a long way)

Ive run a high maintenance import before, and switched to copper as i was at the limit of the stock ignition system, but couldnt justify new coil packs.

I just replaced them every 5oookm with each oil and filter change and never ran into any more dramas... i never tried iridiums.

i would only get 50,000 out of a set of platinums, and would have really bad low load hesitation problems and a rough as guts idle

With all my research i did when building the dedicated 308ci V8 for my HG premier,the conclusion was that LPG requires a heap of intial or "static timing" (dependent on RON and compression etc of course being the limiting factor) and less total at higher revs,We also did away with vacuum advanc eon the dizzy altogether,On my paticular engine,i was running about 20 degrees static and about 10 mechanical for a toal of about 30 degress,Whereas petrol likesl ess inital and more advance higher up,this is where the compromise has to be made,the only advantage would be a few degrees more initial on PULP for a slight gain in botom end

Steve
I have been wondering if driving style can help allow for the different timing of LPG. Here's my theory -

When on LPG, accelerate with a heavy throttle at lower RPM so the vacuum advance advances the timing for it.

At higher RPM, the steeper petrol ignition advance curve catches up to LPG's preferred timing and overtakes it, so just taper back to moderate throttle (under normal economy principles). Are there any engineers that happen to know the typical crossover RPM for this?

The only other unknown is the most efficient cruise RPM on LPG. I'd love to know of any tests at suburban speeds comparing consumption with and without overdrive!