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#1 - 03-13-2014, 4:43 PM.

Much to my surprise I found out that the stock SR20DET plugs were NGK PFR6B-9's pre-gapped at 0.9mm or 0.036". These plugs are laser platinum spark plugs which means both ground electrode and center electrode are platinum. Doing a little research on spark plug types by NGK and metal properties, I came up with some interesting information.

NGK Standard Plugs - Despite people calling these "copper plugs" the center and ground electrodes are actually nickel. All plugs have copper cores, as copper is the best conducting metal vs cost.

NGK Platinum Plugs - Platinum tip, nickel ground electrode.

NGK Iridium IX - Iridium tip, nickel ground electrode.

NGK Laser Platinum - Platinum tip and platinum ground electrode.

NGK Laser Iridium - Iridium tip and platinum ground electrode.

Now, once I determined the different types of plugs I could buy for my SR, I started to research the different properties of the metals used for these plugs (Nickel, Platinum and Iridium.)

Iridium > Nickel > Platinum

I found that Iridium is a slightly better conductor than nickel, but platinum isn't so great... Turns out nickel is about 1.52x better conductor than platinum and iridium being 2.0x more conductive than platinum.

Platinum > Nickel > Iridium

Now as we see here, platinum has the most resistance, which isn't good. Again, iridium is slightly better than nickel with the least resistance. And the values are pretty much the same, platinum having 1.52x more resistance than nickel, and 2.0x more resistance than iridium.

Melting point for each of the metals is as follows:
Iridium: 4471 °F
Platinum: 3214.9 °F
Nickel: 2651 °F

Now, personally I've purchased BKR7E's for my SR20DET from day one. Never had a problem with them and I would regularly change them at 5,000 mile intervals. It costs about $2.25 per plug. So, $2.25 x 4 = $9 every 5,000 miles.

Based on the data above, the best plug in theory would be the Iridium IX. Which is an iridium center tip with a nickel ground electrode. You get the same properties of a standard nickel plug but with the durability, longevity and electrical superiority of iridium at the tip.

Price for a Iridium IX plug for the SR20DET is about $8 per plug. NGK claims you can achieve 40,000 miles out of these plugs no problem. If that is true than we may have a winner here... $8 x 4 = $32 every 40,000 miles.

If I spend $9 every 5,000 miles, than means I spend $72 every 40,000 miles. So, by switching to Iridium IX, not only will I receive superior spark plugs, I will save $72-$32=$40 dollars per spark plug change. The only negative I can see is the gapping of iridium plugs has to be done very carefully. You can't apply any pressure to the center tip or it will break off. The BKR7EIX's come pre-gapped at 0.032" so that is well within spec of our SR's.

I have yet to test the Iridium IX's on my SR since my car is down at the moment, but when I go to fire it up again the Iridium IX's will be in there.

If anyone has any input or personal experiences please let me know!

Last edited by KiLLeR2001 on 03-13-2014, 4:45 PM.
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