Clio mk4 RS: Spark Plug gaps

[Fredsta]

Hi all - My Clio has started stuttering on full boost and I'm hoping that new spark plugs will solve the problem. (only had it remapped about 3 weeks ago).

I've ordered NGK (91215) spark plugs which outline the gap as 0.9.

However, I have read that if you run more power you should be considering reducing the gap. For context, I'm on 300hp, so I was wondering if I should reduce the spark gap and if so, to what gap?

Or am I just overthinking this and should I just stick with 0.9?!

 

[R3k1355]

Did you check the gap was actually 0.9 before the plugs went in?

 

[JamesBryan]

Sounds like a big gap considering the increase in power/boost.

Worth gapping down, try in 0.1mm increments and see if that sorts it.

Wouldn't go too far though, 0.65-0.7mm max.

 

[Fredsta]

Sorry, to clarify: I haven't changed the spark plugs yet, still on the old ones. Havent taken the old ones out yet or inspected them, but was going to replace them anyway.
Ngk ones are en route and was going to put them in with 0.9 gap but thought I'd check if any of you would reduce the gap before putting them in.

 

[JamesBryan]

Sorry, to clarify: I haven't changed the spark plugs yet, still on the old ones. Havent taken the old ones out yet or inspected them, but was going to replace them anyway.
Ngk ones are en route and was going to put them in with 0.9 gap but thought I'd check if any of you would reduce the gap before putting them in.

I would.

 

[Fredsta]

Sounds like a big gap considering the increase in power/boost.

Worth gapping down, try in 0.1mm increments and see if that sorts it.

Wouldn't go too far though, 0.65-0.7mm max.

Thanks @JamesBryan
How did you decide on 0.65 to 0.77 max. Is there a calculator or something?

 

[JamesBryan]

Thanks @JamesBryan
How did you decide on 0.65 to 0.77 max. Is there a calculator or something?

No, just a guess.

My Megane is gapped to 0.6mm so just saying it's no point going further than that.

It's worth noting that the electrode will wear away and the gap will open on older plugs, so you may as well check the old ones first.

 

[R3k1355]

You might just find a new set of plugs with a genuine 0.9mm gap is fine.

If not work down in increments of 0.1mm till you are happy. If the gap gets pretty small, you might be looking at a weak spark being produced?

 

[JamesBryan]

You might just find a new set of plugs with a genuine 0.9mm gap is fine.

If not work down in increments of 0.1mm till you are happy. If the gap gets pretty small, you might be looking at a weak spark being produced?

Yeah too much and you'll get poor combustion.

 

[Fredsta]

Thanks both - will try that first once the plugs arrive 👍