As everyone already knows minimizing the spark plug gap on a boosted engine is pretty much a must due to the increased cylinder pressure associated with boost. But I've always been curious what the negative effects are to having a small plug gap. I mean whats stopping a preson from just gapping down their plugs more on the excessive side to avoid misfiring when the boost is turned up even higher? I am aware of a slightly rough idle and possible slightly worse gas mileage but what I'm really looking for is an explanation more on the physics side of all this. what is causing the rough idle, what is causing change in combustion characteristics, etc, etc. Please list as much detail as possible. thanks

 

nobody???

 

It's called quench.

The center electrode and the ground strap are so close together (compounded by dende charge ignition issues) they block the flame front's propigation.

 

thanks.

please feel free to elaborate a bit more on this..

 

???

 

i dont so much know what the losses r from reducing the gap on the spark plug but basically like u said its a must on forced induction so what u wanna do get the largest gap without it cutting out during boost.

 

Alright, *** nog, I gave you a two word answer before rushing out to work. There's a bunch of things going on here. Ignoring a LOT of things... inductive resistance plugs meant for CDIs, heat range, desireable electrode material (short of coil on plug it's a nonsense argument), etc etc. I'm just scratching the surface here. Put on your waders:

1) Center electrode design.

To help with max coil charging, you want the hardest to jump air gap possible. From an electrical side of things, sharp edges or points help electricity arc over, and keeps the coil from building power for that extra instant. This is the #1 reason why you do not want a pointy dot center electrode, and why you want a broad faced center electrode.

Also. To help with heat dissipation, and to prevent your plug from turning into a big fat hotspot that induces pre-ignition, you want a broad faced center electrode. None of that pointy ****.

Here:


Gay.



Merely effeminant.



Grizzled and manly.

Common rule of thumb is that platinum or iridium is useless, and leaves men with fast cars questioning if you aren't a closet homo based on your plug selection. There are platinum coated real electrode plugs out there, but they are not common. Copper, steel, silver-nickel; these are the center electrode choice of manly men.


2) Gap.

Another way to control how hard the air gap is to jump, is by adjusting the air gap out to create a stronger spark. However, if you get too dense of an air-fuel mix in the combustion chamber it makes the air gap's resistance go up. Soooooo what we try to do is set the gap at the largest we can run without having a lot of plug problems. In a forced induction setup where we really squeeze in some air, the plug's air gap gets really tiny... eventually this causes the center electrode and ground strap to actually block the flame from spreading.



There are a couple of ways to address this.



You can cut back the ground strap so it doesn't block things.


Angle the ground strap... patience and a pair of needle nose!


NGK V-power causes spark to start at the outside edges of the center electrode, allowing the flame kernel to be exposed to much more air-fuel than otherwise possible. They also maintain a larger center electrode to help with heat dissipation and to avoid the hotspot and extreme conductivity problems associated with pinprick electrodes.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by J. Davis &raquo;</TD></TR><TR><TD CLASS="quote">
</TD></TR></TABLE>

You are the man.

Give me some of those books you have over there.

 

Start with Ricardo. Cut your teeth on that, if you can't get a working mathematical model going at least build a working mental image of the general trends being described. After that, I'll probably cover you up with a bunch of hand selected NACA papers, and some of Mean Gringo Bob's musings (some of which are wrong, or misleading, but he was playing with ideas and not trying to be right).

I'm trying to figure out what happened to my copy of Glassman's Combustion. Glassman is a combustion engineer, literally he studied combustion and not engines, and as such Glassman actually knows what he's talking about. I'd like you, and everyone, to read that before you are exposed to Taylor's two volume pack of lies called the Internal Combustion Engine in Theory and Practice.

At that point... before that point... you'll probably have all sorts of questions I'm not equipped to answer. In my defense, nearly no one is. It's always more complex than you think it is, regardless of what level you're on. Great way to spend the rest of your life... other people think you are educated, but you're really just confused.

 

Thanks J. Davis for that write-up, very imformative.

 

I always enjoy JD's informative and intelligent responses while still keeping it real by using terms like "nignog"

 

Great Writeup J. Davis What line of work are you in btw? I'm assuming engineer? I am currently in my 2nd year of mech. e school and this kind of **** is real interesting

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by J. Davis &raquo;</TD></TR><TR><TD CLASS="quote">Start with Ricardo. Cut your teeth on that, if you can't get a working mathematical model going at least build a working mental image of the general trends being described. After that, I'll probably cover you up with a bunch of hand selected NACA papers, and some of Mean Gringo Bob's musings (some of which are wrong, or misleading, but he was playing with ideas and not trying to be right).

I'm trying to figure out what happened to my copy of Glassman's Combustion. Glassman is a combustion engineer, literally he studied combustion and not engines, and as such Glassman actually knows what he's talking about. I'd like you, and everyone, to read that before you are exposed to Taylor's two volume pack of lies called the Internal Combustion Engine in Theory and Practice.

At that point... before that point... you'll probably have all sorts of questions I'm not equipped to answer. In my defense, nearly no one is. It's always more complex than you think it is, regardless of what level you're on. Great way to spend the rest of your life... other people think you are educated, but you're really just confused. </TD></TR></TABLE>

homey you make my head hurt!


good illustrations, glad im a picture person

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SOHC_MShue &raquo;</TD></TR><TR><TD CLASS="quote">What line of work are you in btw? </TD></TR></TABLE>

I am an alcoholic.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by J. Davis &raquo;</TD></TR><TR><TD CLASS="quote">I am an alcoholic.</TD></TR></TABLE>
nothing wrong with that

 

nice write up

is this why the RM plugs work so well?

 

Great write up JD. I really appreciate the time you took to answer this.....very informative

 

bump for some good info

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Chris22215 &raquo;</TD></TR><TR><TD CLASS="quote">is this why the RM plugs work so well?</TD></TR></TABLE>

No, those work so well because Rocket is what is commonly known as a hardcore ************. I'm pretty sure he has a few tricks with plugs that *I* don't know.