3.5V8 - Dual Fuel Timing

[101RRS]

The troublesome 24v ignition system on my 101 has been ripped out and has been replaced with a holden bosch dissy with an early electronic system fitted. The engine (3.5 carby V8) also runs LPG and when installing the new dissy I set up the static timing at the listed 3 degrees BTDC for petrol as I do not know what to set it up on for dual fuel. It runs OK just a little down on power.

So first question - what is the static timing setting for just LPG and what should it be for dual fuel. If I were to set it up to the 'just LPG' setting what would the impact be if I had to run on petrol?

Second question - ultimately I want to buy a more modern ignition system for the dissy, one that will switch ignition timing settings when switching from petrol to lpg etc. Any suggestions on something that might be suitable would be appreciated - also how hard are they to program or do they come pre-programmed.

Thanks

Garry

[Hardchina]

Mate i don't reckon there will be a perfect dizzy setting for lpg. I muck around with mine a bit. I can set it for WOT power but lose big time with cruise economy, or i can set it for cruise which causes it to bog down when flat to the floor. I'm running a comprimise between the two at the moment - If i can find the timing light i'll get a idle figure for ya - but i have a bit of a cam and different manifold, so may not suit yours:(

The only proper option i reckon is going coilpacks and aftermarket ecu.. search here for megajolt. you could get the dizzy regraphed to suit just lpg but you'll pay and it will still be a sucky dizzy.

[101 Ron]

Lpg requires more advance earlier than petrol , but less overal advance than petrol.
Using a petrol distributor for LPG and a LPG distributor for petrol is always a compromise and a timing light and static settings are useless in the real world for a Petrol distributor on a motor running LPG.
Road timing is the way to go and is a compromise and most people or people who lack experience tend to add to much advance when road timing.
My personal thing is to set the motor up with a petrol distributor on petrol to petrol specs and timing light ect and just run the LPG on those settings.( when required to)
A petrol distributor converted to LPG usually has a weaker advance springs on the fly weights and the fly weight stops brazed up for less overal movement for less advance overall.
To do this correctly you need a dyno to test what the real world ignition requirements are for the pacific motor and fuel.
From the readings and information gained and distributor is then set up and and adjusted in a distributor machine.

[101 Ron]

The only way to have your cake and eat it is some form of ignition mapping and adjustment electronically and there are systems out there that can do this and can have two different ignition maps , one for petrol and one for LPG.
The problem is those ignition maps can be a guess unless the engine has been dynoed and the exact engine mapping requirements are known.
There have been some distributors around in the past that had a dual ignition curve set up in them and would be hard to find today.
The real answer is digtal constant engine management and knock sensors ect as per modern cars where the car adjusts itself to the qualities of the fuel the engine is burning.

[101RRS]

My personal thing is to set the motor up with a petrol distributor on petrol to petrol specs and timing light ect and just run the LPG on those settings.( when required to)


Thanks Ron - that is how I set it up. 3 degrees BTDC. Getting reasonable fuel economy on gas but seems to lack a little power. Was thinking 4 or 5 degrees might have been a little better overall but maybe not.

Cheers

Garry

[101 Ron]

Fitting a Hodlen distributor to a Rover motor is wrong as both the petrol and LPG ignition timing will be out of specs to engine needs instead of just the LPG.
If you want to ditch the 24 volt distributor, fit a early range rover one with the early drive on the end as the petrol advance curve will be set for 3.5 litre rover motor and if it is a points early one , pertronix and a few others make a electronic pointless up grade kits.
Ron

[101 Ron]

The slight lack of torque on LPG is not only ignition timing but compression and valve timing not being totally correct for LPG.
LPG motors should have higher compression and slight different valve events to suit the fuel.
Thats another reason why LPG is a compromise on a motor designed for petrol.
Modern car engines with variable valve timing under electronic instant controll run well on LPG.

[101 Ron]

More base advance on the distributor will tend to improve low to mid torque on LPG , but while the motor may not ping, it will run harsher at higher revs and loads and chew slightly more gas,
Better to run less overall advance with a better top end on LPG as this is where the real power is if you needed it and lose out on torque at lower speeds and power settings , like cruising revs on the flat and the loss of torque matters little.
I if doing a trip with my 101 tend to use the LPG on the flatter and better parts of the road and swap to petrol for the hard work for the hills ect and this tends to save engine valves harden seats or not.( the base timing for LPG can be advanced more if this strategy is used)

[101RRS]

What I currently have came out of a 80s rangie - it works fine and will do at the moment. The 24v system had degraded to the point that it was missing badly even with replacement coils and new points, rotor and condensor. The 101 failed to proceed in the desert 80km east of Tibooburra after backfiring and blowing the muffler apart and had to be trailered into town. Two changes of the coil failed to fix the problem, nor did redoing points etc. Once the system was pulled out and my backup bosch dizzy, coil and amp was fitted the problem was fixed - just not sure what the timing should be.

What I am looking for is a dual map amp etc and if that means a change of dizzy so be it.

Interestingly just changing the coil from the original 24v unit to a bosch GT40R (still with the 24v dizzy) improved my fuel economy on petrol from 10.5mpg to nearly 15mpg - regularly getting less than 19l/100km now. LPG was still giving only 10.5mpg but with the full change over to electronic ignition and the bosch dizzy it is now up to just under 15mpg on gas as well as petrol.

Garry

[101 Ron]

Could be condenser on the 24 volt distributor......it will still throw a spark, but it will be weak (in the combustion chamber)and any slight defect in the ignition system will cause a miss fire and points tend to never be working well and sparking on with a faulty condenser.
The original 24 volt leads would best be served with old fashion copper core HT leads replacing the 35 year old items......suspression is not a issuse because of the outer supression cover.
The 24 volt dist should work as well as a 12 volt versions ect expcept for slightly more fuel burn at cruise power settings as it doesnt have vacuum advance like the other versions.

[101RRS]

The only proper option i reckon is going coilpacks and aftermarket ecu.. search here for megajolt. you could get the dizzy regraphed to suit just lpg but you'll pay and it will still be a sucky dizzy.

Can Megajolt run two separate ignition maps that are switchable when LPG is switched on and vice versa?

Garry

[bee utey]

Having a fair bit of experience of dual fuel I suggest you try the static timing on 6-10 degrees. I imagine your driving would not be often at the high end of the RPM range. The use of premium petrol should be able to cope with this amount of advance without problems, especially if you are running 8.13:1 compression. If there is uneven (jerky) running at light throttle you may be able to run without vacuum advance. As far as switching to petrol for hills work is concerned, I don't think you need to do this as the Rover V8 has always been good on gas, I have not seen one with a burnt valve from lpg.
As far as dual timing is concerned, this is only needed in a high comp engine or with low quality petrol. In your case I don't think there will be a problem just optimising for lpg and running good petrol. The distributor you have is specifically built for a carby 3.5 so should work well in the 101. Most of your economy increase will be from the decent spark fully igniting the mixture for the first time in years.

[Hardchina]

Can Megajolt run two separate ignition maps that are switchable when LPG is switched on and vice versa?


Garry

Pretty sure, ive got the megasquirt which does - its been a few years since i looked at the jolt and they were working on dual tables way back then.

[djam1]

Slight hijack but related
I run a 3.5 9.35:1 but am using the electronic distributor from a 1999 Discovery 3.9.
Was at the point of sending the dissy to Performance Ignition Services to get them to change the advance curve.
As the dissy was originally from a 3.9 injected motor should I change the curve?
FYI I have used this dissy for the last 5 years and have had nothing but perfect running on LPG if I advance the timing on LPG its great but I figure I shouldnt really run 12 degrees all the time particularly on ULP.

[400HPONGAS]

What alot of rooting around, Easy fix , Crane -HI-6 with TRC-2 in dash retarder . will do exactly what you need . Plus or minus 10 degrees of advance / retard adjusted on the Fly . Pick em up Egay for $150 US , wouldnt never run LPG without a Multiple spark Discharge system .

[Hardchina]

What alot of rooting around, Easy fix , Crane -HI-6 with TRC-2 in dash retarder . will do exactly what you need . Plus or minus 10 degrees of advance / retard adjusted on the Fly . Pick em up Egay for $150 US , wouldnt never run LPG without a Multiple spark Discharge system .

the trc retard unit looks like a good setup for a soopped up engine where performance or economy at part throttle aren't issues - but i reckon its way too basic for anything else. Still left with limited range crappy vac advance, springs and weights, sloppy gear driven shafts controlling a pretty important aspect of engine tune. None of that matters though if you drive with the right foot planted to the floor - and with 400hp on gas who wouldn't :p

[101RRS]

Having a fair bit of experience of dual fuel I suggest you try the static timing on 6-10 degrees. I imagine your driving would not be often at the high end of the RPM range. The use of premium petrol should be able to cope with this amount of advance without problems, especially if you are running 8.13:1 compression. If there is uneven (jerky) running at light throttle you may be able to run without vacuum advance. As far as switching to petrol for hills work is concerned, I don't think you need to do this as the Rover V8 has always been good on gas, I have not seen one with a burnt valve from lpg.
As far as dual timing is concerned, this is only needed in a high comp engine or with low quality petrol. In your case I don't think there will be a problem just optimising for lpg and running good petrol. The distributor you have is specifically built for a carby 3.5 so should work well in the 101. Most of your economy increase will be from the decent spark fully igniting the mixture for the first time in years.

Thanks for that - I was amazed at the 30-50% improvement in fuel consumption from just changing to the GT 40R coil. I was surprised that the bosch dizzy did not have an oil O ring on its main shaft housing like the rover one has - as would have let out oil from the engine - silastic around the top of the clean housing fixed that. I will try about 6 degrees BTDC and see how we go.

I am also surprised at the complete lack of waterproofing on the bosch dizzy - will need to work on that one as the 101 will stop with just a little splash of H2O. The ignition amp seems well protected though.

Oh - and my tacho does not work with the electronic ignition. The needle flops around 1500rpm irrespective of engine speed and when the engine is at constant revs it settles back to indicate 1000rpm. Is there a special way to connect the tach or do I need one for electronic ignitions. I have it currently connected to the coil as per the previous arrangement.

Garry

[101RRS]

None of that matters though if you drive with the right foot planted to the floor - and with 400hp on gas who wouldn't :p

Driving a 101 on the highway is with right foot planted to the floor with the massive 90kw V8 nudging 100kph with 2800rpm on the dial. 400hp would be nice though.

Garry

[Hardchina]

Driving a 101 on the highway is with right foot planted to the floor with the massive 90kw V8 nudging 100kph with 2800rpm on the dial. 400hp would be nice though.

Garry


:) I'm just cracking the butterfly at 100kph - 2500rpm (ish) in fifth

why do you want dual fuel? you could mount 10,000L worth of lpg tanks around the 101?

[101RRS]

why do you want dual fuel? you could mount 10,000L worth of lpg tanks around the 101?

It is already fitted with dual fuel - as I had to start playing around with the ignition system I thought I would have my cake and eat it too and try to maximise efficiencies on both petrol and gas by fitting a dual mapped ignition system.

Garry

[400HPONGAS]

garrycool , at the end of the day the optimised advance might gain you say 5% in power , ****all really . The reason Dual fuel setups are crap is the Dynamic compression ratio , unless you can change that from 9:1 to 11:1 (thats the difference in static,overlap will determine final dynamic)then everything else is just a compromise . I build either straight gas engines or staight ULP engines , never dual fuel !!

[Hardchina]

garrycool , at the end of the day the optimised advance might gain you say 5% in power , ****all really . The reason Dual fuel setups are crap is the Dynamic compression ratio , unless you can change that from 9:1 to 11:1 then everything else is just a compromise . I build either straight gas engines or staight ULP engines , never dual fuel !!

Yep, thats why dizzys suck - they're ok for all out power, tuned for either, but can't do the job properly if you're trying to setup for dual fuel.

I reckon it's worth the few hundred bucks and the mucking around with coilpack ignition + the dyno tuning, you'll get it back in fuel saved in no time.

you have to be committed though... do you really love your rover Gary? Show it you care. You'll both feel all warm and fuzzy after.

[400HPONGAS]

Regardless of how many coil packs you put on and how you manage them , they still wont to do as good a job as a proper specced MSD system , especailly for LPG .

[bee utey]

Thanks for that - I was amazed at the 30-50% improvement in fuel consumption from just changing to the GT 40R coil. I was surprised that the bosch dizzy did not have an oil O ring on its main shaft housing like the rover one has - as would have let out oil from the engine - silastic around the top of the clean housing fixed that. I will try about 6 degrees BTDC and see how we go.

I am also surprised at the complete lack of waterproofing on the bosch dizzy - will need to work on that one as the 101 will stop with just a little splash of H2O. The ignition amp seems well protected though.

Oh - and my tacho does not work with the electronic ignition. The needle flops around 1500rpm irrespective of engine speed and when the engine is at constant revs it settles back to indicate 1000rpm. Is there a special way to connect the tach or do I need one for electronic ignitions. I have it currently connected to the coil as per the previous arrangement.

Garry
The dissy is probably sealed as in the Holden with a gasket under the clamp ring. Silastic will be fine.

I have rally driven P76's through quite deep water in the past, so long as the lead boots are tight and waterproof, the only extra protection needed is to stop water lifting the cap and getting under the edge. I found that a circle of electrical tape around the top of the distributor body helped, just carefully push the cap on over the tape. You might also consider a splash shield to protect the cap from direct impact of a load of water.

Sad to hear the tacho doesn't work here. It may be feasible to fit a series resistor in the tacho wire to reduce the pulse size, although I haven't tried this. The issue is that electronic switching is not quite to zreo volts, unlike points which do so. I have seen older VDO tacho's misbehave on electronic ignitions, I seem to remember some had adjustable triggering on a screw on the back.

Oh and I suggest you ignore anyone trying to make you spend $$$ on dual or otherwise fancy ignition systems. As suggested your gain will be minimal on the low comp engine. Talking efficiency and standard 101 in the same sentence isn't sensible.:)

[Hardchina]

Regardless of how many coil packs you put on and how you manage them , they still wont to do as good a job as a proper specced MSD system , especailly for LPG .


The coilpacks don't do the magic, Thats done by the little computer that works out the exact spark timing, based on rpm, air flow, intake air temp, engine temp, fuel type, manifold vacuum, throttle posistion..

for an every day engine that needs to run on dual fuel they run rings around a msd dizzy system. Even set for just one type of juice they would poo all over a dizzy. You bag the rover for been old design then bag new tech ecu ignition because old 1920's based crap is better :confused: It doesn't matter how fat a spark the msd spits out - if it's doing it at the wrong time whats the point? BTW stock coilpack pack a decent punch./