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MSD coils tested got 45 , 48, 50 mm so better than the best other coil at 41.5mm, would be interested to see if brand new ones are the same

did you test back to back with the others to exclude atmospheric condition influences? Pretty interesting results so far.

Results are always the same, never found atmosphere to change the results

That's interesting results there, have read for years that the MSD coils are a waste of money and do nothing better than stock.

Yeah, not what I expected either...

im using 2 of these, so the spark is enclosed so conditions would be relatively stable.

http://www.ebay.com.au/itm/272478410025 ... EBIDX%3AIT

working on the link here, Air breaks down at about 30 kV/cm
https://en.wikipedia.org/wiki/Spark_gap

So best N/A coil 41.5mm 124,500v
Best MSD 50.0mm 150,000v

Question is does the extra voltage make much difference. I know VL400 with his LS driver and coils made a difference i dont know what voltage they delivered.

After those results I'll happily leave the MSD coils on the Calais

The1 wrote:So best N/A coil 41.5mm 124,500v
Best MSD 50.0mm 150,000v

Question is does the extra voltage make much difference.

On a bog stock n/a engine with "street" compression (so it could easily run on 91 octane) extra voltage doesn't make a difference. On a modified engine with higher compression or even boosted beyond OEM levels extra voltage does make a difference.
Voltage is just electrical pressure. Spark from low voltage can be snuffed out if an engine has high cylinder pressure, so higher voltage (more spark pressure) is able to withstand higher cylinder pressures.

Yeah, that's spot on.

I'm running MSD coils with a 3.4" pulley, getting about 11psi max in the LIM and I'm fairly damn sure my plugs are gapped at 1.3mm where everybody says you need to use 1.0mm gaps for 10psi or you get an ignition miss.

In theory, if you have lots of spark energy than you should be able to open up your plug gaps, bigger gap, stronger spark. On my old VN I fitted new plugs when I first bought it and lost at least 50km's per tank of fuel. Pulled the new plugs out and they were gapped at 1.3mm which is the recommended gap for that engine, re-gapped to 1.5mm and found that mileage back. Interestingly the old plugs that came out were well worn, gaps were all in excess of 1.6mm and not a hint of a miss-fire, they were original AC Delco plugs from Holden too and must have been in there forever (it was a 1 elderly owner car when we bought it with only 68,000km on it).