While for stock or near stock I wouldn't recommend a colder plug, what I do think we need is a NON 100,000 mile plug. Those have proven to missfire with turbo applications after only a few thousand miles of use due to the tip style.I think this is one of those things which can only be answered after people are able to get tuning...heavy tuning may require something colder if a colder plug does exist...here is a broad breakdown of why you would want a colder plug, this is from the NGK website:
Increases in firing-end temperature are proportional to engine speed and load. When traveling at a consistent high rate of speed, or carrying/pushing very heavy loads, a colder heat range spark plug should be installed
Advancing ignition timing by 10° causes tip temperature to increase by approx. 70°-100° C
As air temperature falls, air density/air volume becomes greater, resulting in leaner air/fuel mixtures.
This creates higher cylinder pressures/temperatures and causes an increase in the spark plug's tip temperature. So, fuel delivery should be increased.
Lean air/fuel mixtures cause plug tip and cylinder temperature to increase, resulting in pre-ignition, detonation, and possibly serious spark plug and engine damage
As compression increases, a colder heat range plug, higher fuel octane, and careful attention to ignition timing and air/fuel ratios are necessary. Failure to select a colder spark plug can lead to spark plug/engine damage
As humidity increases, air intake volume decreases
Result is lower combustion pressures and temperatures, causing a decrease in the spark plug's temperature and a reduction in available power.
Air/fuel mixture should be leaner, depending upon ambient temperature
Barometric Pressure/Altitude also affects the spark plug's tip temperature
The higher the altitude, the lower cylinder pressure becomes. As the cylinder temperature decreases, so does the plugs tip temperature
Many mechanics attempt to "chase" tuning by changing spark plug heat ranges
The real answer is to adjust air/fuel mixtures by rejetting in an effort to put more air back into the engine
That may not be every instance to worry about spark plug heat ranges, but I think it covers the question. As for our cars, until a lot more tuning occurs on a dyno, we may not know, with definite certainty if we should change plug heat ranges. Without being able to adjust cam/crank timing, ignition timing and changing the turbo, I'm not sure going to a different plug will really matter...someone can chime in and correct me if I'm wrong of course...
NGK makes an OEM replacement. Slightly pricey. They are about 11 to 12 bucks a plug. They are the NGK Laser Iridiums. Part no. 3811 or full item number is ILTR5A-13Gmakes since. my z was heavily modded. So I've done some searching and ngk doesn't have a replacement that i can find should i stick w/ oem
If those NGKs are TR6s, then we could potentially go with a NGK TR6 copper plug. You can get those for about $1.49 each. I run those in my supercharged Mustang and they work very well.I took my stock plugs out the other day because I thought they were causing my problem of surging at cruising speeds. They looked like NGK plugs, but were labeled with FoMoCo, which I am assuming is Ford Motor Company. To get to the point, the plugs had a TR6 in the model code. Does that mean that the NGK plugs are actually a hotter plug? I thought the TR# was the heat range...if this is the case, I am wondering why they would be selling a plug with a different heat range...
I also noticed in a picture that the threads were very long. Wonder how long until more plugs are available.Yeah i have some TR6's laying around from my mustang as well and after seeing the stock plugs they are definitely not the same. Our plugs are a deep well style plug...meaning the threaded portion goes very deep into the head...so as far as i've found, no copper plugs available yet...