Logic Behind Spark Plug Gap.

[TheBassist]

Okay, so I've heard all of the different spark plug gaps for both the 420a and 4g63, but what I want to know is why?

I read on here that, generally, the more power you have, the smaller the gap should be. And vice versa. Why is that?

Why is a larger gap better for N/A and a smaller gap for F/I. And, on a related note, what effects would I see (driving my 2gNT) in widening or narrowing the gap?

Thanks!

 

[blackrosenova40]

As you increase cylinder pressure, the resistance across the gap increases. Using the logic electricity takes the shortest path, if you increase your cylinder pressure too much, it may not fire as the resistance across the gap is too high. So what do you do? Decrease the gap of course.

 

[steve]

You actually want a large a gap as you can reliably fire but as pointed out the higher the cylinder pressure the harder it is (more voltage it takes) to reliably get a spark across a gap. That's why the turbo cars run a smaller gap than the NA's.

 

[TheBassist]

Ah, that clears it up! Thank you! And so...people sometimes get upgraded coil packs and such to deliver a stronger spark so they can maintain a fairly wide gap still?

Thanks again.

 

[talontsi1225]

Factory coils can put out 80kv if they really need to but normally only work at 40 -60%. Gas is a conductor, air isnt. So if you try to compact more air and fuel in the cylinder the spark would have a hard time to jump the gap with all the compressed air.

 

[sprmotohooligan]

Side question that is related: Whats the recommended gap for a 4g63t anyway??

 

[RadDsm]

side question that is related: Whats the recommended gap for a 4g63t anyway??

.028

 

[steve]

Gas is a conductor, air isnt.

You sure? If it was you might have some difficulty starting back in the fuel tank where there are live wires immersed in the gasoline to power the fuel pump.

 

[blackrosenova40]

Factory coils can put out 80kv if they really need
to but normally only work at 40 -60%. Gas is a conductor, air isnt. So if you try to compact more air and fuel in the cylinder the spark would have a hard time to jump the gap with all the compressed air.

This makes no sense. If air wasnt a conductor, spark would not be able to occur. Its just not a very good conductor. As cylinder pressure increases, the reisistance increases.

Im not sure if it works this way, but would the resistance across the gap be twice as great at 1 bar versus no boost if the engine ve, engine speed, and intake temps were the same?

 

[PewPew90Laser]

As you put more stuff into the cylinder, resistance increases. Period. Air does not conduct electricity, Gasoline does not conduct electricity but with a high enough voltage electricity can use them as a medium as they are not insulators.

When you decrease the gap, spark resistance DECREASES meaning it takes less energy to cross the gap. On the other side with a decreased resistance there is a stronger flow of current so the spark retains LONGER. The secondary circuit of the coil has more energy to disperse across the field.
When gap is larger, more resistance means the coil has to generate a larger kick to cross that gap and the spark time is shorter.