105 series spark plugs

[Willy Hilux]

What spark plugs do you guys use for dual fuel in a 105 series 1fz-fe motor? Run mostly on lpg.

Cheers
Aaron

[geoffro46]

we use the standard plug in them without problems.

[evanstaniland]

I just got some on friday, Gas man got me some Champion C9YC and took 10% out of the clearance in the tip. think it was 1.1mm so we reset them at 1mm

Evan

[RAY185]

I try to avoid champion plugs in favour of NGK or Nippondenso. There must be a NGK catalogue online to look up plugs for your vehicle. They might specify a particular plug for LPG but generally you just use the same as standard but 1 range colder. Eg if they list BP5EY-11 you should use BP6EY-11 (bigger the number, colder the plug). Also as above, often the gap is closed 0.2mm if LPG is going to be used a lot more than petrol.

[Northside 4x4]

Whats the reasoning behind closing the gap up for LPG applications?

[RAY185]

Combustion temps are higher and the charge is more dense in an LPG application which means the spark needs more voltage than it would for petrol to jump the gap. Much easier to reduce the distance it has to jump than to increase the spark voltage.

[Northside 4x4]

Combustion temps are higher and the charge is more dense in an LPG application which means the spark needs more voltage than it would for petrol to jump the gap. Much easier to reduce the distance it has to jump than to increase the spark voltage.

Well the combustion temps dont really play a part in the plug gap?

And why/how is the charge more dense? Same amount of air in, less fuel per part of air and its literally gas instead of incompletely vapourised liquid droplets.
Gas lambda 1 is 15.5:1 as opposed to ULP's 14.7.

So i dont really understand the theory behind it.

[RAY185]

Perhaps my choice of the word "dense" was incorrect. Open any spark plug manufacturer's catalogue and you will find advice about LPG vehicles and spark plug selection. Pretty much every one of them uses the terms "higher temps and higher pressures" as reasoning for choosing a cooler plug and closing the gap to remedy the higher spark voltage required on LPG.

The fact that LPG is a dry fuel and is known to be harder to ignite than petrol is enough for me to buy the argument that it needs more spark. I've never had reason to question it any further. If you have the time, look into it and let me know. I'll happily continue to refer to the catalogue's advice for plug selection until then.

Here's a couple of examples but I'm sure you have some catalogues of your own to check. (NB: Bosch don't talk about gapping as they sell a line of dedicated plugs for LPG use so they are already gapped accordingly).

There are two critical factors that need to be understood when converting a vehicle from petrol to LPG:

LPG burns hotter
LPG increases the voltage requirement at the electrode gap
In an attempt to correct these two factors, as a general rule we suggest to:

Use a spark plug that is one heat range colder than standard to compensate for the increased heat from LPG:

The temperature profile of an engine may vary between vehicles. As such, the effect of LPG on the operating temperature of one vehicle may not be the same for another vehicle.
For example, lets say that LPG increases the average operating temperature by 200°C. If the average operating temperature of a Holden Commodore (which uses a 6 heat range) was 700°C the addition of LPG would exceed the operating range of 870°C. As such a colder plug may be required. However, a Ford Falcon for example (which also uses a 6 heat range) may have an average operating temperature of 500°C, the addition of LPG is still within the 450 – 870°C operating range and a colder plug may not be required. Please note that these values have only been used for illustration purposes.

Reduce the electrode gap by 0.1mm to compensate for the increased voltage:

It is difficult to gauge exactly how much the voltage requirement has changed as other factors such as engine wear, loss in compression and ignition system weakness for example may provide an influence. As such the electrode gap may need to be adjusted several times until the correct gap setting is achieved for that unique vehicle.

Dual-fuel or single-fuel, petrol or LPG; all spark-ignition engines work in the same basic way. This fact allows almost any petrol engine to be easily and economically converted to LPG.

However, there are some significant differences in how an engine functions when it runs on LPG compared to petrol.

Combustion chamber temperature.
When petrol enters the combustion chamber, evaporative cooling occurs. This cools the spark plug and other components (“charge cooling”). Since LPG is not a liquid, it burns dry, so there is no charge cooling effect. That means the combustion chamber and spark plug electrode are hotter.

Higher voltage requirements.
As the internal combustion temperatures and pressures are higher in LPG engines, they need higher spark voltage for ionisation (the spark to jump the
electrode gap) than petrol engines. Where a petrol engine might need 14 kV, the same engine but with LPG would need 16 kV (see figure 1).

Heat range
LPG vehicles require spark plugs with a colder heat range, to prevent pre-ignition.

Life
Higher temperatures in the combustion chamber and high voltage result in accelerating spark plug wear.
Therefore LPG spark plugs need to be changed more often than spark plugs in petrol vehicles.

And also page 12 of the AC Delco catalogue which I can't copy and paste for you. http://www.acdelco.com.au/PDFs/Catalogu ... 0Plugs.pdf" onclick="window.open(this.href);return false;

[geoffro46]

i only only close the gaps if they backfire and i dont trust champions either. i doesnt hurt to go 1 colder in the heat range but it doesnt really matter. closing the gaps only really helps if your ignition system isnt up to the task. cruisers are usually ok but i close up mitsubishis and holdens.

[Northside 4x4]

Good read, thanks for taking the time to post that up.

I think alot of the ignition questions comes down to the fact that gas is a higher octane rating and naturally harder to get burning than ULP.
I didnt see that mentioned in those snippets you provided.
I made a post in another thread regarding ignition timing on gas vehicles last week.

Dont take my posts the wrong way, im just curious to see what peoples opinions are on these things, and its always good to bounce idea's and thoughts off other people.

[Willy Hilux]

Ok, I got around to change my plugs today. Went to Supercheap and the NSK book said for a 105 series 4.5L 1FZ-FE ....... BKR5EKB-11. So I went one cooler and grabbed 6 x BKR66EKB-11. I didn't worry about making the gap any smaller.

The old ones in there were DENSO K16TR11. The old ones were pretty white looking as well. This might be common for gas but I'm new at LPG.

I've only done the one run to work, so I'll see if the miss has gone. If not then I'll fork out for leads.

[geoffro46]

the plugs do stay pretty clean on gas usually a little discoloured at the top of the porcelain its the electrode u need to look at to see if its had it.

[Willy Hilux]

Still have the miss when driving. Guess I'm up for new leads.