Spark Plug Gaps, MSD, smoothness

[jameshtaylor]

I have a very sweet running 2.7 with a few mods and an MSD. For years I've heard that I should open up the spark gap to .045"--.050" (from the .032 I've been using) with NGK 6's. Steve Weiner and others have noted increased power and smoothness at the bigger gaps. Well I finally got around to trying this. Quite amazing. There may be more power, I can't really tell, but the motor is easily 20-30% smoother, at idle and at speed!
Anyone know why? I'm guessing that a wider plug gap means that current is stored a millisecond longer and that perhaps more of it is released when the plug fires, but why would this affect smoothness? Whether or not anyone has the answer, increasing the gap has produced a very noticeable improvement with which I'm delighted.

[Steve@Rennsport]

Hi Jim,

I'm very pleased that you took my advice and tried the big plug gaps,.. I don't offer something that I haven't tried and know to work as claimed,...

The large plug gaps help create a larger flame kernel that burns hotter. This ensures more thorough fuel/air combustion in the small amount of time it has before TDC.

The engine dyno doesn't lie and we see more HP with these larger gaps over the factory-specified ones. One simply must have an ignition system thats sufficiently powerful to strike and sustain the spark.

[CamBiscuit]

Does this also apply to a twin plug system fired by a single MSD?

[orange911]

What does this mean with a 2.4T w/ MFI and Bosch ignition module? Am I to presume that they too require larger gaps? If so, how much?

Olin

[jameshtaylor]

I'm not an expert but my guess is no...probably because the Bosch doesn't send enough volts to jump a bigger spark gap. I think the factory would have gone for more power and smoothness if it could have been achieved so easily.

[orange911]

Volts to the coil:
Bosch CDI - ~400 Volts
MSD - ~500 Volts

So about 25% more volts, which equates to about 10,000 volts to the cylinder using a standard 100:1 coil (40,000 vs 50,000). But you opened the gap by about 40-45% more. Maybe there is some room to open it up with the stock system.

Olin

[jameshtaylor]

I'm doubtful but you have little to lose. If it won't start, or your secondary wiring gives out, you'll know you've gone too far!

[jeff eelkema]

I always thought MSD stood for multiple spark discharge so you have a much better chance of getting a good spark at the plug.

[jameshtaylor]

It does and you do (at least under 3k rpm...the multiple spark feature goes away at higher rpm.)