Spark Plug Heat Range

[XfireZ51]

I did a scan of a standing start going thru 3 gears last week. I got Knock retard at top of third gear. So now I’m wondering if that was happening at track at BG. I pulled plugs to see if there were signs of pre-ignition or was it false knock. There were some tiny specks on porcelain but sooty not metallic, and right at the edge of porcelain as it goes horizontal towards center electrode. Also, looking at the ground strap, it changed color at the weld suggesting heat range was hot. Base ring color was black telling me WOT fuel could be leaned out.Plugs were barely torqued so I took care of that. I may do another scan and see if I get same results. If I do, I may go to a slightly colder plug. Right now using AC 41-630 having replaced the NGK Irdiums TR5IX (Came with car, so no idea how long they'd been there) that were there.
Anyone want to chime in on which plugs and heat range they're using?

Here's a very interesting quote from this article

http://www.articlealley.com/article_467790_31.html

"...When an engine is modified for high performance and its power is increased, the stock spark plugs very often result hottest than necessary due to the new power reached at higher RPM and the gasoline would end up pre-igniting or detonating without the need of an electric spark, creating an uncontrolled explosion that would severely damage the engine.

Be aware that never! Never a high performance modified engine, can continue using the stock spark plug, because more power is more energy, and more energy always is more heat.

Unfortunately, even very experienced mechanics have difficulty in detecting the differences in these situations that are very often misunderstood, misleading them to search the origin of the troubles that the spark plugs are showing, in the supposedly wrong air/fuel mixture, cooling systems troubles or other mechanical failures.

It is absolutely clear that is doing lack more information about the true one and transcendental importance of the heat range of the sparkplugs. This exact selection is critical!

Only with the proper Heat Range will spark plugs sustain the perfect combustion process that keeps your engine's top efficiency and functional reliability.

But only a few of the most selected and experienced engine tuners know how to select the spark plug with the proper heat range best suited to match these different conditions, or the specific engine's level of modification, but them reach it only after long hours of expensive and difficult testing by trial and error with different spark plugs sets of different heat ranges.

What you need to find is the spark plug with the heat range, best suited to the combination of your own specific, individual and particular driving habits, traffic, weather, and engine operating conditions, fuel quality, that can be affecting your engine performance; tailoring this selection exactly for you driving habits or life style.

This is the only way that guarantees to achieve the peak power, performance, endurance, better mileage and the lowest emissions."

[flyin ryan]

o.k., i'll bite. i didn't cross the AC number over yet but are you sure the NGK's you had were 5's & not 55's? 55's in our cars is common. the way your reading the plugs sounds like you almost right on the money. i would go one range colder than you are now. i see guys jump to colder heat rangers way too quick most times IMO. it sounds like in your case your on top of the situation & have a good idea what your doing though. i use NGK's in all my stuff, Zee's & the engines i build. 4's are hot & 10's are ice cold. for example the Competition Eliminator engines i do make anywear from 2.35 to 2.5 H.P. per cube & i use 8's & once in a while 9's in then. off coarse that's all naturally asperated stuff. 10's are strictly maximum effort power adder combinations. now there are thousands of factors that make up your plug choice & i don't know 999 of them right now. in a nutshell i think your close.

[-=Jeff=-]

I used 41602 Ac Delco in my car, why did you go with the 41630?

[XfireZ51]

Originally Posted by -=Jeff=-

I used 41602 Ac Delco in my car, why did you go with the 41630?

Your car meaning the 89 or the ZR? That's what Al suggested and I believe they are the equivalent of the NGKs. There must be some other difference between 630's and 602's. If its heat range only, one of us if WAY off.

FR,

The NGKs I had were the TR5IX Iridiums. As the article said, the more power you're making, the more heat your putting in. Therefore the need for colder plug. I don't think I'm that far off either. But its enough to make a difference and worth investigating.

[-=Jeff=-]

Originally Posted by XfireZ51

Your car meaning the 89 or the ZR? That's what Al suggested and I believe they are the equivalent of the NGKs. There must be some other difference between 630's and 602's. If its heat range only, one of us if WAY off.

Sorry the 41602s are in my Z

[XfireZ51]

Originally Posted by -=Jeff=-

Sorry the 41602s are in my Z

Jeff,

Isn't there also an issue about the plug seat on the 90 head being different?

[flyin ryan]

90-92's are flat seat. 93-95 use a taper seat. some guys use a taper seat in 90-92's, it'll work but it's not right.

[Aurora40]

Originally Posted by XfireZ51

The NGKs I had were the TR5IX Iridiums.

The NGK Iridium plug listed for the '93-95 is the TR55IX. I wonder if the TR5IX is just some older identifier? I believe one range colder is the TR65IX, and two is the TR75IX.

This is a tapered seat plug, which is not correct for the early LT5. However, if it's already in there, I wonder if you'll need to use tapered plugs from now on?

[XfireZ51]

Pete,

I'm positive its a 41-630. But I will look again when I get home. One other
possibility is that if I do have heads with tapered seats, it would give more evidence that the motor had in fact been replaced as I was told. Supposedly, original motor had cam seize issue and GM replaced it with a new one. Sepaking with Ron Kreigh at BG, he said that the service engines were all 4 bolt, 93+ motors. Curiouser and curiouser.

[Aurora40]

Originally Posted by XfireZ51

Sepaking with Ron Kreigh at BG, he said that the service engines were all 4 bolt, 93+ motors. Curiouser and curiouser.

Wouldn't it depend on when it was done? If it seized in 1990, I doubt it would be a '93 engine.