Hey ya'll. So since i installed my EFI the truck has ran well, but, I am sure that i am not burning as much fuel int he chamber as i could be, the exhaust smells of richness. The AFR ratio is good, depending on throttle position I'm anywhere from 12.5:1 to 14:1 on AFT. Now, i am using NGK V groove plugs gapped @ .035 (stock recommended), however, I'm running a petronix with blaster coil and 8.5mm Moroso Wires, so I'm sure my ignition system can pump out enough spark to accommodate a bigger gap, thus burning more fuel, but I'm not sure where to start. I could bump it up to .045 but i know guys that run that stock just fine, i dont want to over gap either though, i was thinking about setting them @ .050 and going from there.

Thoughts?

 

I'd bump the plugs up to 0.44+ as the Duraspark ll the plugs where set at 0.44.

You could play with your timing a little also. but if it pings you may need to change you vacuum advance some. Take notes so you can go back a little if to much advance or timing. Check spark plugs after a few hundred miles that you burning a good plug color.
Orich

 

Wider plug gaps and such came about because of the difficulty of reliably firing lean fuel mixtures (16-1 or more) The wider plug gaps are generally more abusive esp. to stock (point type) ignition components.

 

IMHO those V plugs are a gimmick and should go away. I would buy some standard Ford ( Motorcraft) part number BSF42C (SP420) copper core spark plugs. Gapped at .044/.045. In the pic above I don't see how one can gap them correctly. If gapped where the spark is shown in the pic above then the gap in the center is much wider. The spark will go where it wants too. Not necessarily the closest point. Usually, yes. But maybe not always. I prefer simplicity myself.

 

Tedster is right, wider gap is to better fire lean mixtures. You can try wider and wider gaps, if you get it too wide, it will miss under load as the richer mixture will "put the fire out". I agreed with the others, see if .044 will work and, if so, I would leave it at that.

 

Some pretty knowledgeable folks in the ignition field will argue that the plug gap is mainly a function of the cylinder head design, and consequently always recommend using the factory gap specification regardless of whether the ignition has been upgraded or not. In this case probably .035"?

I like side-gapping plugs. Indexing plugs doesn't hurt anything either, didn't notice any power difference or anything like that but the exhaust note definitely changed for the better at idle. It is fun to experiment.

 

This seems to say that fuel mixture has nothing to do with it and I cannot go along with that.

 

I don't think that's the case, the fuel mixtures were taken into account at the time of the design, no? The wide gaps really took off when OEM were trying out "lean burn" strategies. I think it was GM who went off the deep end for a little while, and had .060" gaps and were burning up ignition rotors and caps.

The points type distributor cap and rotor diameter is a lot smaller than electronic ignition components and can run into trouble with excessive plug gaps, the voltage required to jump the plug gap goes way up.

 

2X Jas. Not very often I disagree with something Ted mentions. But I have to here. Back in the 60's and early 70's the plug gap was always .035 for American V8's. Ford, Chevy, and Chrysler. No matter what heads. Once electronic ignition hit with it's hotter coils the gaps widened. Except I see the Dodge 318 was .035 all the way up to 1990.
But, maybe what those knowledgeable folks are referencing is some Buick, Olds, and Pontiacs had .030 or .040 back in the day.

 

Right, but I'm not saying that I agree with them necessarily, but I can see their argument. Electronic ignition pretty much debuted right in the middle of the smog era, when they also changed a lot of engine characteristics - lower compression, retarded ignition timing, and lean highway fuel mixtures. Their recommendation seems to be if you're running a pre-smogger engine from the 50s thru 60s, keep the stock gap.

So the question might be did they widen plug gaps later on because they could or, because they had to? It does increase average coil temperature and the likelihood of crossfire in the wires, arcing inside the points style distributor cap.

I don't think any harm can come from running the stock spec gap at any rate, what do dyno pulls indicate? Is there a measurable performance difference?

 

I have always assumed (yeah, I know) they widened the gap to help burn everything in the cylinders. Lower emissions. The hotter coils allowed them to do this.
As far as the cross fire goes, That's prolly why in 1975 with the electronic ignition Ford came out with a Blue Dizzy cap and rotor. Obviously made out of something different. Then in 1977 Ford came out with the 2 piece larger diameter Dizzy cap and rotor. This widened the gap between terminals to cancel out the possibility of crossfire in the cap.
The 1977 and newer 2 piece cap and rotor will fit right on to a points Dizzy BTW.

 

My living comes from tuning large bore lean burn engines. I don't even have to gap the plugs more than .035" because I use a multiple spark ignition system. It fires 4 times instead of once and that increases the amount of time the spark is active in the cylinder. With an 18" bore (no typo) and natural gas coming in at only about 15 psi, it doesn't make a homogenous mixture when I lean an engine out due to emissions limits. So it can be hard to light. The downside to firing four times is that the metal that is transferred from one electrode to the other happens when the arc is started, But I need the increased duration time to be sure to light the lean mixture.


A wider gap will erode the electrodes faster than a narrow gap due to the increase firing voltage (as mentioned above). In a small bore automotive engine .044 is plenty and still not really needed to ignite the mixture. All of the sparks are the same temperature and that is what ignites the mixture.


If the AFR is ranging from 12.5 to 14.1 you can move the fuel mapping a step or two leaner. If you want the most power possible you want to stay around 12.5:1

 

Here is a single ignition duration lasting just a little over 1 millisecond. This ignition is negative firing to save a little bit of wear on the electrodes, automotive systems are positive firing.

 

 

Here is a multi strike lasting about 6 milliseconds.