Warning Brisk LPG spark plugs

[classicswede]

I recently had a car come in for service with a very bad misfire while under any load. It was so bad the car was almost undriveable. With all other components changed including new coil packs the only possible cause had to be the special LPG plugs fitted by the owner.

After removing the Brisk silver LPG spark plugs that were almost new (only a couple of thousand miles) and fitting a set of NGK copper core plugs the misfire had almost totaly disapeared, with a bit of remapping solved.

Looking at the plugs you can see they have no hope of working well with LPG. LPG likes a single spark path and the Brisk plugs have 4. You could see on each plug that 1 path was black, the 2 paths to the side had a thin black line and the other path was totaly clean. The sparks were not able to track each path at all with only 1 making a resonable spark 2 intermitant and the other almost not at all.

My advice is to save yourself some money and avoid these plugs especialy with turbo engines.

The best plugs to have are a simple basic single electrode copper core plug.

[Ian Donkin]

Dai's just converted our 3.2 XC90 and the plugs were the original iridium coated OEM Ford parts with 45,000 miles on them... They were playing up within 500 miles of the conversion so we've now gone with some standard NGK's at around £4 each!

I changed them myself whilst chatting on the phone to one of my mates and still did the whole lot in 20 minutes - no running problems since :-)

NGK has a technical support department here in the UK and they are, as you'd expect, very knowledgable and very helpful too. Full marks to NGK (and Dai on our conversion).

[Gareth83]

single prongs should be used on any application to be honest regardless of LPG converted or not.

extra prongs just make them last longer

[classicswede]

The extra prongs are not there to increase life.

The idea is that they should give a stronger and broader spark. The effect of the stronger spark can give a small increase in power upto 2% and improved MPG upto 2%.

The problem is LPG is not conductive like petrol so the ignition system is strained and more power is needed to create a spark. Under these conditions the spark will not travel to each prong as there is not enough power there and the spark will only take the easy path. The end result is uneven sparking and misfiring.

NGK are helpfull and will advise on the best plug for your engine running on LPG.

[Clan]

The idea of multi prong plugs is indeed ONLY long life , basic electronics say the spark will always take the easiest path , it is impossible for the plug to have multi sparks on each prong at the same time unless it is fed with huge amounts of HT energy..
what happens is that the spark takes the path of least resistance which is the prong with the shortest gap , as this wears, the gap gets wider and eventualy the next unused prong is the easiest path and that one starts to get used , and likewise until that wears and the third prong starts to get used etc , that is how volvo plugs last 72000 miles ..
You may choose your particular plugs that work right with your LPG, however if you use it on petrol often you will find the genuine volvo plugs give the best performance of all . Volvo ignition systems are and always have been very powerful and really should cope with lpg , they always did fine in the 1980s-1990's-2000's what's changed ? .. I guess genuine volvo plugs were not tried first on this problematic engine ..

[classicswede]

The issue is purely down to spark plugs. As already said muti prong plugs are problematic and should be avoided with LPG.

Most of the Volvo plugs are still single electrode items but the tip material has been changed to platinum or iridium depending on age/engine. LPG eats platinum spark plugs and they will last from a few hundred to a few thousand miles. Iridium plugs are fine with LPG but last no longer than a basic copper core plug.

[Gareth83]

Originally Posted by classicswede

The extra prongs are not there to increase life.

The idea is that they should give a stronger and broader spark. The effect of the stronger spark can give a small increase in power upto 2% and improved MPG upto 2%.

Originally Posted by Clan

The idea of multi prong plugs is indeed ONLY long life , basic electronics say the spark will always take the easiest path , it is impossible for the plug to have multi sparks on each prong at the same time unless it is fed with huge amounts of HT energy..
what happens is that the spark takes the path of least resistance which is the prong with the shortest gap , as this wears, the gap gets wider and eventualy the next unused prong is the easiest path and that one starts to get used , and likewise until that wears and the third prong starts to get used etc , that is how volvo plugs last 72000 miles ..
You may choose your particular plugs that work right with your LPG, however if you use it on petrol often you will find the genuine volvo plugs give the best performance of all . Volvo ignition systems are and always have been very powerful and really should cope with lpg , they always did fine in the 1980s-1990's-2000's what's changed ? .. I guess genuine volvo plugs were not tried first on this problematic engine ..

This was my point they only extend plug life in reality. In theory 3 or 4 prong sounds great but they run no different in any situation.

Did you know that there can ONLY be ONE ARC at a time when your spark plug fires????
Sorry, but you will NEVER EVER have two, three or four electrodes fire at once.
It's called " Physics". Take out a plug and lay it on your engine block and see for yourself. Just have a friend crank your engine and see. Go ahead.
Thats why a single electrode is the hottest most efficient source of spark.
The double sand quads only have an advantage if the plug becomes "fouled" on an electrode.
Then one of the others will be able to continue in a best case scenario.
My friend is an engineer for NGK. He's the one who told me all the skinny on this.
All of it is Marketing to sell more expensive plugs to people who are not informed.
Now you are informed.
Don't waste your cash.

I have also read on various forums multiple prongs particularly Bosch have snapped a prong and resulted in sticking valves. I'd rather stick to single prong but gap/change them more often