On the gap...
Grimes is doing the head work on my engine this week (see Chad's TJ in projects for more information) and I asked about the spark gap and what I got in return was a sinister grin.
My interpretation of the dialogue that followed is this:
1) if it sparks it works
2) if it doesn't spark it doesn't work
3) spark plugs don't add power
4) upgraded ignition system with the same gap as a non-upgraded ignition system will generate a "hotter spark" but a "hotter spark" does not mean more power
5) shorter gap is "easier" to jump than a larger gap so an upgraded ignition system "maybe" more resistant to failures related to lack of spark
In the end I summarized that I had not wasted my money on the ignition system because it is in theory more reliable but that the only way it was going to add power would be if the old system wasn't actually working properly. I still didn't understand what his recommendation on gap really was but I gathered he didn't think it really mattered as long as we were getting spark.
I completely agree.
If the stock system is inadequate, the engine wont run smooth, especially at lower RPM's due to erratic igintion. Running a more powerful coil that sends more energy to the spark plug will often make an engine run better by igniting more consistently.
The spark plug starts the burn, and the flame front spreads through the combustion chamber. Running a hotter spark and larger gap will only ensure there is no misfire, but does nothing to speed up the flame front (which is where the power is made).
The only ignition systems I have seen that actually make a difference in power are the multi-spark-discharge (msd)type. And if you do the research, you will see that these only do msd below 3k rpm. Above 3k, it doesnt seem to make a difference. I dont really have an explanation as to why they make more power.
Engines that run two plugs per cylinder will loose power when one plug is pulled, because you have now cut off one flame front and it is taking the mixture twice as long to burn across the combustion chamber.
As far as plugs go, the platinum and iridium ones are more durable. Try to run standard plugs with a high power coil and you will see the spark eat the electrodes on the plug over a few thousand miles. The platinum and iridium ones prevent this from happening.
I currently run a Summit digital ignition on my 2.5 (MSD below 3k rpm and adjustable rev limiter). I found no noticeable power difference between this one and the stock Ford DUI that was on there. My main reason for this ignition was to have an adjustable rev limiter, and I was hoping it would make more power and better fuel mileage.
Food for thought: some of the highest power-per-displacement production engines on the planet, motorcycle engines, also run some of the weakest coils and no msd.
