Spark Plug Gaps - Necessary?

[EViS]

I have purchased a set or Iridium NGK plugs to install into my V8. Being the first LPG vehicle I have owned, I'm wondering how important it is to actually check and adjust the spark plug gap with a tool? Is it a relatively pointless exercise on modern engines?

If it's worth doing, should the gap be adjusted to the plug manufactures spec, the vehicle manufacturers spec, or a universally recommended gap for LPG?

[Gilbertd]

Leave them as they are. NGK Iridium plugs aren't designed to have the gap altered anyway (although clouting them with a plug spanner will close them up if you hit them hard enough).

[luke123]

I think what Gilbert is trying to say, gapping down the Iridium plugs is not advised.

How ever some cars spark plugs just work better on LPG gapped down and some are fine with the standard plug gap.

If im right the 4.4 v8 Should be alright with the standard plug gap

Luke

[scottyf]

No issues with the Alfa they use Iridium tips. Didn't change from the standard gap even on petrol.
Then again it has two sparks a cylinder which is annoying.

Will the spark plugs take a battering now its on lpg?

[luke123]

No issues with the Alfa they use Iridium tips. Didn't change from the standard gap even on petrol.
Then again it has two sparks a cylinder which is annoying.

Will the spark plugs take a battering now its on lpg?

I have always understood it this way.

LPG is a dry fuel and requires a better spark for it to burn efficiently, of the top of my head IM sure it's got something to do with it having a lower calorific value than other fuels.
And IM sure it burns at higher temps than petrol so the spark plugs often require changing a little earlier.
I have found Japanese vehicles require the spark plug gap lowering alittle as they misfire using the original gap that manufacturers say.


Luke

[scottyf]

I understand about it running hotter on the exhaust side and valves. But always aired on the side of rich. Although not sure if it matters so much using lpg and the cylinders dont really get cooled by petrol.

[Gilbertd]

LPG needs a better spark as it is more difficult to ignite, it also has to be much closer to stoic or it simply won't ignite in the first place. On petrol the mixture can be miles out and the engine will still run, badly but run. On gas it has to be much closer to optimum. LPG does burn hotter but the difference is marginal (I seem to recall petrol burns at 1730 degrees and Propane at 1750 or thereabouts). Normal copper plugs will generally last around 10,000 miles on LPG before they have eroded to the point that the gap gets too big for efficient ignition but Iridium ones, or Iridium NGKs anyway, will last 4 to 5 times that. So on an alloy head it's a good idea to put a bit of graphite grease on the threads when you put them in so you can get them out again in two or three years time......