NGK 5673-7 or -8?
 

Guys,

Wondering which heat range will be better for me.

454, Dart aluminum heads, 8.8:1, B&M 250, 6-7 pounds of boost. I think most will say go with the 8's but I was wondering if the 7's may be better because of the aluminum heads and cold water (crossover, no-tstat).

Thoughts?

Also, anyone know of chain stores that stock these or something equivalent? Having to wait a few days to get spark plugs is annoying.

Thanks!

If this is a real clean running motor try the 8s if not put the 7s in. There might be some other plug numbers you can run maybe a outboard supply may have something in the heat range and thread you are looking for. Also might consider a resistor plug will help with RF noise.

I ran the 8's in my supercharged 454s with similar combo, as well as autolite AR134's. Never had any issues in all the years I've ran them. .

The motor will tell you what kind of plug it wants.

. FWIW, mercury used the delco MR41T and the NGK 5673-8 plug, which comes in a merc box under part # 33-8134214 in the 525sc and 600sc carb supercharged engines. That 5673-8 plug, is usually inventoried under the "3249" part number at O'reillys auto, autozone, etc.

http://www.oreillyauto.com/site/c/de...2&keyword=3249

In an engine like a supercharged marine one, running at higher rpm's for great lengths of time, esp with a small blower, a decent amount of ign timing, the plugs can get pretty hot! Unless you have a really awful tune on your carb, and a weak ignition system, fouling a -8 NGK, should not be a problem. I've ran them for years, and they've seen some really long idle times, and can't I've ever fouled one unless something went wrong, like a carb needle sticking and flooding the engine. I've always been a fan of starting with a colder plug, and working your way up, rather than a hotter plug, and working your way down. The results of too hot a plug, can be much more costly, than too cold of a plug.

If the spark plug used in an engine is too hot for its application, it could result in:
•Excessive rate of electrode erosion, excessive gap growth
•Center and ground electrode damage (burned or melted)
•Damaged engine valves
•Damaged pistons due to excessive pre-ignition

If the spark plug is too cold for its application, it could lead to:
•Misfires due to fouling

On the dyno we were using -7s and had trouble getting things to heat up, but the blower was weak. I guess I should have added that at the beginning. Anyway, I've ordered a set of -8s, and should have them in the morning (good'ole NAPA).

I do agree that the motor will tell me what it wants... I just don't want it burning up in the process!

Only down fall on the #8 they might not clean them selves well at low power. Start there and see if you have problems fouling them. Think you will be ok with them.