Supercharged M20, forged pistons chipped/cracked!!

[Daveaholliday]

Right. Its been 2 hours!

I've been going over my research on plug gaps and I'm still not entirely sure if 0.025 is that bad.

I've not seen anyone, anywhere recommend 1mm yet, many 0.7-0.8mm, 0.022-0.035" depending on set up and even a few of those lower ones don't have the original spark set up.

I found this quote amongst others:

'The 08-10 N54 factory turbo BMW's come with .0275" plug gap and I have read that its recommended to drop to .022" in high boost applications.
I would start at .025" or so.'

Most of the research seems to go with these figures, I know its a different engine but its a BMW and the higher the boost, the lower the gap needed, no?

Would you imagine a VR6 coil pack can deliver enough spark to withstand 18-20psi at a gap on the top of the given brackets and why has my research not led me to the same conclusion as you? What could I be missing?

Yes you would reduce the gap with higher boost but only if required. The more mixture you can light the quicker the burn and overall the safer/more detonation resistant burn. It's all fractions but power gains are all about a fraction here and a fraction there.

On an NA engine with a good COP set up the spark energy should be enough to jump a 1mm gap no trouble, If you look into the COP conversions the yank V8s do and COP conversions for the MX5s etc then you find they are erring towards .035-.45" gaps (0.9-1.15mm).
That much gap would probably blow out at 18psi though, which is why you run less gap.

The stock single coil and dizzy set up is about average for spark energy, yet 0.8mm gaps are fine NA and with a good setup 0.65mm are ok boosted.
There's no way the VR6 coils are worse than the single coil, 2 air gaps and 6+ feet of HT lead.

I have noticed BMW stuff seems to be either very conservative or 10 years behind what other "scenes" are doing.
To me 0.022" (0.55mm) seems ridiculously conservative for a modern ignition system. That's the gap remote control cars run, really it says the ignition system is not up to the job. (wonder if that is due to making the coils light/cheap on the N54?)

Stepping outside the BMW world:
http://www.saabcentral.com/forums/showt ... p?t=177007 (1-1.1mm)
http://www.fordownersclub.com/forums/to ... -plug-gap/ (1-1.3mm)
http://miataturbo.wikidot.com/spark-plugs (.025" stock coil .035-.050" with toyota COP)
http://www.evolutionm.net/forums/evo-ge ... g-cop.html (.028" in similar condition to yours)
http://forum.miata.net/vb/showthread.php?t=319593 (0.05" gap with 15 PSI )

Rule of thumb - more powerful ignition system = more gap possible
More boost = less gap.

I would be gaping to 0.8mm and only brining them down if there's signs of misfire. If the spark blows out you will go rich, in which case gap down.

Thanks for that.

I think what you are saying makes total sense and is my understanding but I just couldn't find any proof of anyone doing larger gaps on forced induction. I was also reading about symptoms like cutting out and I was experiencing this also so felt a smaller gap was ideal. Quite possibly the gap I have used is taken from someone using the standard sparks.

I'll go up to .8 and try it out - when the engine finally fires back into life

Going for bigger gaps too.