manual ignition advance

[100I]

I've been giving some more thought recently to ignition timing.
With dual fuel you can't have it both ways - or can you...

I primarily run on LPG, as you do, but also
(a) regularly run petrol to keep the system up to scratch,
(b) run out of LPG and flick to petrol to get to the next fill,
(c) flick to petrol for more power :twisted:.
On LPG overall it can also lack torque, at idle, off road, and just tends to be plain unresponsive. (This may still just be mixture tuning, still playing with it)

part1 I'm currently running 14deg advance and it is still very happy at that on 98ron, in fact it goes very well. Now maybe I'm expecting too much of an old school low compression engine, but as I said on LPG it still feels a little lacklustre. Although I haven't as yet I will experiment some more with timing aproaching closer to 18 or even 20deg but Mr Magoo can see it will NOT like that on petrol. Also that might give too much total advance anyway so a recurve of the dizzy may also be in order. Has anybody gone to the trouble of recurving their dizzy for LPG and was it worthwhile? If so how has it affected it on petrol? Can you give me specs to get it graphed to?

part 2 The offshoot of all this is I also had the idea of rigging some sort of cable adjuster to adjust the timing, aka vintage cars. I this getting too complicated for my own good? Do you think a mower style wire cable would be strong enough? My base idle will change is the first problem that comes to mind.
Anybody got some specs, tips, ideas or thoughts on this?
Or care to just heckle me?

cheers

[langy]

I can't comment on your LPG settings, but there is a far better way to have two different timing solutions -

Try this kit:
http://www.siliconchip.com.au/cms/A_108521/article.html

There are various professional units around, but they are in the performance class of gear.

[100I]

thanks fellas,
Langy, that's a LOT more civilised that a mower cable:D
That's ultimately what I would have prefered but just did not realise it was possible without resorting to a full aftermarket ECU and coil packs. Brilliant.
PLR, yes my understanding is that LPG likes a lot of intial but not too much total.

I found the below here http://www.centuryperformance.com/timing.asp
"It is our recommendation that when you are using vacuum advance distributors, that you connect the vacuum advance to "full manifold vacuum". There are two schools on where to connect the vacuum advance line. On older applications the connection point was to "ported" vacuum. Ported vacuum means the port is drawing vacuum "above" the throttle blades in the carburetor. This means that as RPM increases, vacuum increases and in turn, vacuum advance increases. This was fine on older applications with high lead fuel and other ancient engine designs. Using this set up today can cause detonation problems, overheating, and other grief.
With our suggestion of using the vacuum connection to full manifold vacuum, the port will be drawing vacuum below the throttle blades. A good running street engine will have a measured vacuum at idle between 14"-20" of manifold vacuum. Now, this will give you a ton of advance at idle, but as load increases (vacuum drops) you will take timing away. This is excellent for the faster burning fuels offered today as well as in the fact that when you put your foot into the throttle and get the RPM building, you DO NOT need or want additional timing. On a RV or tow vehicle, when you put your foot into the throttle and downshift to climb a grade, you DO NOT want added timing that will slow the vehicle and add heat. You want the added timing for subtle throttle response, and low load engine efficiency. So, when you are cruising at freeway speeds or in town traffic, you have the added timing to save fuel, add throttle response, and overall give you a better feel."
Now from my memory (the LR is not here at work to look) the vacuum advance is ported just to the outside of the butterfly. With this in mind I think I'll modify to full manifold vacuum which should achieve what I want for LPG. I'm thinking I could then just quickly remove and plug the vacuum line for extended petrol use if it is too brutal. Although with 98ron and being a low comp engine it seems to be pretty tolerant, whereas the use of low grade petrol would make it impossible to tune for both - this is probably where most people come unstuck, as the cheapskates who put their car on gas also put cheap fuel in them:p

Onboard switchable advance curves would be the ultimate though so I'll keep looking into that.

EDIT. If fiddling the vacuum advance works well I could jerry rig a solenoid in the vacuum line to a switch in the cab.

[100I]

Ok so that's some good numbers to shoot for to start with. Seat of the pants always wins but a base line helps get started. thanks.
I just double checked my RAVE cd and it does say to set dynamic timing at 800rpm max with vacuum disconnected, however I have removed the vacuum hose before at idle and there was not so much as a cough (and the vac advance unit is working perfectly and I have various new vacuum hoses).
My hunch is that as far as petrol goes it'll end up losing top end power but if it's grunty enough I'm a happy short shifter 95% of the time anyway.
So I'll put some of this theory into practice & see how I go.

[Bulldog]

thanks fellas,
Langy, that's a LOT more civilised that a mower cable:D
That's ultimately what I would have prefered but just did not realise it was possible without resorting to a full aftermarket ECU and coil packs. Brilliant.
PLR, yes my understanding is that LPG likes a lot of intial but not too much total.



Hi guys,

Has anyone done a distributorless ignition system? I've got the bits of a Ford EDIS-8, coil packs and a trigger wheel... Not installed yet. You can get the controller from the "megasqirt" (or "megajolt") website, but I'm gonna DIY my own software and sensors for a bit of fun. One of my reasons for doing all this is having a Petrol/Gas setting.

[Blknight.aus]

the jaycar delay kit based on a 555 timer is a good bet but limited in what it can do for you...

Id be looking at rigging up a second vacume unit that holds the dizzy in place as opposed to the bolts that stop it from turning...

apply vacume to it and the advance is adjusted accordingly.

[100I]

:thumbsup:

Well I tee'd off the vacuum hose from the stepper motor's manifold. It is definitely running a lighter throttle on the open road. There's a good big long test hill on the Ippy hwy that I use to compare adjustments. It sailed up tonight at approx 1/2 pedal in 5th, whereas it was almost if not completely flat to floor before. Here's hoping economy improves accordingly but the way I hustled it along tonight I'll have to wait till next tank to find out:rolleyes:

Only a couple of glitches; resetting my idle (geezus I hate that feckin stepper) and I have a small flat spot if you could call it that at about say 1800RPM, not a hiccup or cough, just goes thru a trough where it's fallen off the vacuum advance and the mechanical isn't quite up there yet untill a bit over 2000rpm. It's not bad, it's just there, lighter springs would probably sort it. It doesn't pull like a 14yr old from idle to redline.. yet, but it's reasonably strong from off idle to about 4200, which is fine, and more than it had before, with over-rev left to spare. Seemed happy enough on petrol too.
Going to take a bit more than an hour's work of an evening but it's got promise.
:burnrubber:

[100I]

;) update.
The boss drove it today and she reports that it keeps accidently creeping up to 110. :D

[Frontier1]

This is all well and good, but what do I do since I have electronic ignition and both LPG and Petrol? ( 1993 Disco' V8i )

I have adjusted the timing as far forward as I can for LPG but when I flick over to petrol, she pings like a MF! ( although if I run her with a light foot she goes OK).

I too want to be able to click from one timing to another to suit both and all these chips seem to be for older/carby style motors.

I did look at the Megasquirt option a while back but it didn't appear to be viable at the time.

I have been wondering about a dyno-tune to see whether there is other ways it can be tweaked.

Cheers, Pete'

[100I]

Try this simple mod first

[Frontier1]

Once your happy with what you've done, including any additional little mods, can you post a step by step? I'm sure that there are more than a few that would be very interested in giving this a go.

[Bradtot]

Yeah me I am very interested very very am waiting each minute for updates please
Brad.....have ya done:wasntme: it yet?

[Frontier1]

Yeah, I realised that AFTER I sent my post. One too many wines I guess! :)

[100I]

A brief update; this last tank of LPG returned over 5.1K/L, up from a consistent average 4.7K/L, doesn't sound much but it does add up. The engine does have more HP, and has a much cleaner & healthier note down the exhaust. Just feels stronger all round, in that you feel the engine making a real go of it rather than just winding out. All for the cost of some vacuume hose and a tee, 3mm was all I could get on the day but a 4mm tee would be a snugger fit. Haven't touched anything else yet & can't for the life of me find my timing light anyway, so can't plot the specs for you but I am still at 14BTDC at idle plus whatever the vacuum advance is giving, probably 6-7. This vacuum advance of course has come OFF the total at high RPM so it is much stronger top end as well. First 3 gears it's strong, 4th is improved & although it doesn't accelerate up hills in top cog it holds speeds now (hey it is still only a 3.9). Will put some pics up later when I have some numbers. Cheap simple mod, nana could do it.

[Bulldog]

thanks fellas,
Langy, that's a LOT more civilised that a mower cable:D
That's ultimately what I would have prefered but just did not realise it was possible without resorting to a full aftermarket ECU and coil packs. Brilliant.
PLR, yes my understanding is that LPG likes a lot of intial but not too much total.

I found the below here http://www.centuryperformance.com/timing.asp
"It is our recommendation that when you are using vacuum advance distributors, that you connect the vacuum advance to "full manifold vacuum". There are two schools on where to connect the vacuum advance line. On older applications the connection point was to "ported" vacuum. Ported vacuum means the port is drawing vacuum "above" the throttle blades in the carburetor. This means that as RPM increases, vacuum increases and in turn, vacuum advance increases. This was fine on older applications with high lead fuel and other ancient engine designs. Using this set up today can cause detonation problems, overheating, and other grief.
With our suggestion of using the vacuum connection to full manifold vacuum, the port will be drawing vacuum below the throttle blades. A good running street engine will have a measured vacuum at idle between 14"-20" of manifold vacuum. Now, this will give you a ton of advance at idle, but as load increases (vacuum drops) you will take timing away. This is excellent for the faster burning fuels offered today as well as in the fact that when you put your foot into the throttle and get the RPM building, you DO NOT need or want additional timing. On a RV or tow vehicle, when you put your foot into the throttle and downshift to climb a grade, you DO NOT want added timing that will slow the vehicle and add heat. You want the added timing for subtle throttle response, and low load engine efficiency. So, when you are cruising at freeway speeds or in town traffic, you have the added timing to save fuel, add throttle response, and overall give you a better feel."
Now from my memory (the LR is not here at work to look) the vacuum advance is ported just to the outside of the butterfly. With this in mind I think I'll modify to full manifold vacuum which should achieve what I want for LPG. I'm thinking I could then just quickly remove and plug the vacuum line for extended petrol use if it is too brutal. Although with 98ron and being a low comp engine it seems to be pretty tolerant, whereas the use of low grade petrol would make it impossible to tune for both - this is probably where most people come unstuck, as the cheapskates who put their car on gas also put cheap fuel in them:p

Onboard switchable advance curves would be the ultimate though so I'll keep looking into that.

EDIT. If fiddling the vacuum advance works well I could jerry rig a solenoid in the vacuum line to a switch in the cab.

Ummm, can someone simplify this a bit more for me please. It sounds like your saying to block a vacuum hose to the dizzy on LPG for more power/ecomony... as simple as that? :cool:

[100I]

With the ported (before butterfly) vacuum to the advance unit the more you open her up the more spark advance it gets, beginning at say 5BTDC factory setting.
Trouble is LPG doesn't like that, it prefers the other way round, so you want to start off with plenty of advance but not too much total.
What that article's theory was, and therefore what I did, was to supply full manifold vacuum to the advance unit on the dizzy.
I easily did this by teeing into the vacuum hose from the stepper motor's adaptor plate/manifold (whatever you wish to call it) which runs to the fuel pressure regulator on the injection rail.
It works. At idle and to a limited amount of throttle opening the spark is fully advanced. As you open the throttle, manifold vacuum drops and the spark is allowed to retard.
However, there is a soft spot in the power band around the 1500-1800RPM (NOT a loss, just not improved as well as everywhere else), as the mechanical advance requires modification to alleviate this.

[jasper110]

Ummm, can someone simplify this a bit more for me please. It sounds like your saying to block a vacuum hose to the dizzy on LPG for more power/ecomony... as simple as that? :cool:

i'd second that! how about a twin carb set up? i have strombergs. i tried the vacuum advance hose to a point on the manifold that was blanked (between the 2 carbs) and the idle was terrible. i've curently blanked the vacuum advance and plugged the original take off for it on the L/H carb. it does seem to run and start better, but this could be placebo. more info please (and pics)

[100I]

This might be a silly Q jasper but is your vac advance diaphram intact? Or do you mean it idled high?

[jasper110]

This might be a silly Q jasper but is your vac advance diaphram intact? Or do you mean it idled high?

idle is solid when ported to the carb. when ported to the manifold as mentioned, it's all over the place. the unit itself is sound.

[Utemad]

Hi Dan,

How's this mod going?

I'm going to give it a go this afternoon.

When my LPG was fitted I was told it was set at 10 deg BTDC and I haven't touched it since.

If I get this right then what I have got from this is that with the vaccuum advance connected before the butterfly the vaccuum advance gets more advance at idle and less at higher revs (than standard after butterfly) which is better for LPG.

If it works then I'll fit a 12v solenoid to switch the vaccuum lines when the fuel used is changed.

[Utemad]

I did the change yesterday afternoon. Teed it off the vacuum line for the fuel pressure regulator. Seems to have more go on LPG but will see how it goes over the next few tanks/weeks.

[Bulldog]

i'd second that! how about a twin carb set up? i have strombergs. i tried the vacuum advance hose to a point on the manifold that was blanked (between the 2 carbs) and the idle was terrible. i've curently blanked the vacuum advance and plugged the original take off for it on the L/H carb. it does seem to run and start better, but this could be placebo. more info please (and pics)

I'm glad this thread has resurfaced, i forgot about it ;)

Is this method from jasper110 correct for a twin carb setup (strommies). Exactly which point does it connect to on the manifold? I would be interested to know if the improvement is real or a placebo...