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[joff]

OK, as I'm about to do a bit of work on this 2.6, which are the best plugs to use with a Stag 300+ system fitted as I know you lot have tried them all. Just as well do them now I'm going to do the cam belt and water pump. This car needs some TLC engine wise

[tigers_gonads]

Standard GM twin's imo
Larger flame front works better with lpg then quads 

[Marks DTM Calib]

Its not so much the size of the flame front, its the fact that fewer electrodes cause less shielding of the spark and hence the flame front and ignition is faster. 

[tigers_gonads]

Its not so much the size of the flame front, its the fact that fewer electrodes cause less shielding of the spark and hence the flame front and ignition is faster. 

That's what I meant, clever git 

[chrisgixer]

I use the standards 4 electrode ones personally. I don't buy the shielding theory myself. But each to their own.

What ever you decide, nothing special is required for lpg.

[TheBoy]

Both my LPG Omegas are running GM twins


Which reminds me, I think the Silver Bullet's ones may have done about 50k . Job for later in the summer

[Kevin Wood]

Just to be different, I'm running triples. Delco, IIRC.
The myth of needing harder plugs for LPG probably originates from those who set them up too lean.

[Marks DTM Calib]

Yes, I suspect you are right Kevin.

However, the spark shielding with mutli electrode plugs is a reality Chris (and easy to visualise) and there are even some very fancy 'non/minimal electrode' plugs (check out the likes of the surface discharge ones used on Wankel engines where any protruding item gets wiped out by the rotor tips) available to counter it.

The extra electrodes are only there to in theory lengthen service intervals so a design compromise. 

If going for ideal, you would use single electrode plugs with the open end facing the inlet valves.

And if you still don't believe it, look at the likes of some Hondas where the plugs are indexed form the factory for best combustion and you can buy plugs with an indexed value! 

[chrisgixer]

I don't believe the omega lump is tuned to a point that it will make use of it. Ok, if looking to eek the last bhp out of the thing then fine. But as we know, its tuned for torque not high rpm. A quick combustion seems less important on a low(er) revving engine in a road car. I don't believe that combustion will be incomplete as a result of extra electrodes, put it that way.

But specific to lpg fitted engine bays, and ignoring all aspects of combustion admittedly, the agro of getting the plugs out of 246 bank is only added to with extra lpg plumbing in the way. The longer life is a factor for me on quads.

But then again there's the consideration for the plugs working loose so getting in there to re torque means they may as well be changed.


I think its a greater benefit to owners to look at stopping the plugs coming loose and gaining the best life from the plugs. Rather than issues associated with the number of electrodes.

 If an lpg fitted car is set up correctly there is zero noticeable difference to the driver between petrol and lpg. I also see the difference in combustion qualities between lpg and petrol as a greater issue to combustion. Greater that is than two extra electrodes on a spark plug.

[chrisgixer]

Just to add, I was going to go off to google and look into it. But if talking to the master I'm sure I'll get far more sensible and educational replies direct.

[Marks DTM Calib]

I don't believe the omega lump is tuned to a point that it will make use of it. Ok, if looking to eek the last bhp out of the thing then fine. But as we know, its tuned for torque not high rpm. A quick combustion seems less important on a low(er) revving engine in a road car. I don't believe that combustion will be incomplete as a result of extra electrodes, put it that way.

But specific to lpg fitted engine bays, and ignoring all aspects of combustion admittedly, the agro of getting the plugs out of 246 bank is only added to with extra lpg plumbing in the way. The longer life is a factor for me on quads.

But then again there's the consideration for the plugs working loose so getting in there to re torque means they may as well be changed.


I think its a greater benefit to owners to look at stopping the plugs coming loose and gaining the best life from the plugs. Rather than issues associated with the number of electrodes.

 If an lpg fitted car is set up correctly there is zero noticeable difference to the driver between patrol and lpg. I also see the difference in combustion qualities between lpg and patrol as a greater issue to combustion. Greater that is than two extra electrodes on a spark plug.

Highly tuned is actually not the key here, its all about igniting the fuel at the correct time and burning it as this gives maximum combustion efficiency (and possibly more power but questionable).

Modern cylinder design is such that some swirl is created (hence why you try to keep inlet gas speeds up with multi rams etc.), you want the swirling fuel air mix to be passing over an exposed spark gap.

The more electrodes you add, the more turbulence you get, the more disruption around the spark gap you get.

Hence, as is clear from the theory, multi electrodes give but one thing, extended service life (and often greater cost) at the expense of compromising, on any engine, the ignition of the fuel/air mix.

I hope that gives a bit more insight.