Chris,

I know its probably too late, but you might really want to go to a colder plug with the SC. You're generating a lot more heat and a colder plug will help you keep the plug at a proper operating temperature. Just for reference, I'm now three heat ranges colder than stock on my SC'd CRX.

UL

 

Yes -
On the flip side, setting up to colder on N/A cars - the plugs could foul out. Running the IK24's instead of the 22's on a N/A might not allow the plugs to reach their optimum temp. Platinum plugs require a larger gap than steel. I'm not sure about iridium. U/L, whats the deal on those?

Basically it goes like this {from grassroots m/sprts}

- The size of the gap... arc-over voltage is roughly proportional to the gap size

- The air/fuel ratio within the gap... the richer the air/fuel ratio (more gasoline vs. Air), the lower the required arc-over voltage

- The compression at the moment arc-over is to occur... the higher the compression, the higher the required arc-over voltage

- The composition of the electrode... certain metals for all the same conditions stated above will require less arc-over voltage than other metals. For example, platinum requires less arc-over voltage, all other things equal, than does steel

- The shape of the electrode... the sharper and more jagged the shape, the easier it is for voltage to jump

- The amount of fouling deposits trying to remove the electron flow from the arc... more fouling deposits and lower resistance to ground pulls more energy out of the spark gap.

 

Denso claims that their plugs require about 5 kV less to arc over a given gap (amounts to about a 20% reduction for an average car). If this is true, then you could conceivably run a larger gap. This would create a larger flame kernel and theoretically aid ignition by exposing more mixture to the start of ignition. However, you would diminish the benefits of having a lower arc voltage when it comes to mixture, heat, compression, etc. And at some point a larger kernel doesn't mean much.

I don't know if the lower voltage requirement is due to the conductivity of iridium (I doubt it) or the extremely small size of the electrode (more likely). Because iridium is so hard, and therefore durable, Denso can apparently make the electrode much smaller than a comparable platinum or copper plug. Interestingly, the iridium plugs come pregapped and the gap gets smaller for colder plugs. For my CRX, it was about where I was running the gap anyways, so it wasn't an issue. I don't know about platinum requiring a larger gap than copper plugs though. Platinum actually has worse electrical conductivity, and thus, if the electrodes were the same size, would need a smaller gap.

I agree about fouling out plugs on NA cars, although I find that going one heat range colder usually has no drawbacks. On a higher compression engine or one that sees lots of racetrack or high speed driving (or hot weather) one heat range colder should be mandatory IMO.

UL

 

That's a good point and I don't get it myself - The specs we run on boosted SR motors are .28 f/ steel and .34 for plat. The FSM says pretty much the same.

[/QUOTE]On a higher compression engine or one that sees lots of racetrack or high speed driving (or hot weather) one heat range colder should be mandatory IMO.[/QUOTE]

Without a doubt