Spark plugs for blown combo

[H.G. Wells]

I searched and read a couple different threads on spark plugs, but did not see this addressed and would like some guidance.

Finally got to make a few passes this weekend with a 496, alky, Merlin iron heads, 8:71, around 6 lbs of boost, SM3 (hopped up by Spud) and built enough heat to read the plugs. (a little lean)
Not sure if I am ahead or behind.

Running a Champion  670 v59c picked up cheap from one of the guys with a similar combo.
Not a fan of Champion and always ran NGK with my inject small block.
Gapped at .016

I do not know enough about heat range to pick what I need, so what heat range do I need? NGK R5674-10 or do I need to go to a hotter -7?
Are the heat range number standardized between brands? bigger# is colder?

[fedonnitro]

I looked at my old cross reference chart and found everything except up to date stocking numbers. I went to a place I use from time to time to find the current stock numbers.  www.sparkplugs.com  Your current Champion plugs are 14mm, taper seat and .460 reach- correct? If so then you can use a NGK-R5673-8, stock #3249 that crosses over very close. If you want to use an NGK I would use a NGK-R5673-9, stock #3442 or better yet maybe a NGK-R5673-10, stock #4050. For NGK's the higher the (-**) dash # the "colder" the plug. For these particular Champions the lower the # the "colder" the plug. If you stay with Champions a V55C, stock #668 might be a better choice.  sparkplugs.com has a heat range chart that helps show the difference between several brands also. I use a NGK-9 in my blown alky small block. Hope this helps.

Carl

[ricardo1967]

IMO, NGK-10 is unnecessarily too cold for 6psi of boost on alky.

[H.G. Wells]

Thanks, that is the kind of info I need.
Yes 14mm and I will have to ck on the reach but that is probably right.

More boost needs colder plug?
Any advantage to longer reach plugs that are indexed vs a short reach?

[dreracecar]

I run a standard NGK b9es plug, since I tune to an index anything just about works and did not notice any change when I  had to bum a plug (dropped it) and the only one was a 10.  The easiest way to read a NGK plug is to count the number of threads that the iridite is burned off, 3 threads is safe 4 is on the edge. Autolight is not plated and Champions are nickle plated which makes reading really difficult and I am too cheap to put egt's on the car

[ricardo1967]

... The easiest way to read a NGK plug is to count the number of threads that the iridite is burned off, 3 threads is safe 4 is on the edge...

Bruce, I've heard about this method before, can you say more? I assume it would work only once? Once the three or four threads are burned off, can you still read thread counts, for example, if you run richer again?

[dreracecar]

Once the plating is gone to 4 its useless to get another reading, but the plug is still good.
Again I tune to an index, Tuning a 6.80 car up/down to a 7.00 leaves me on the fat side so my plugs dont see even 3 threads discolored.

[ricardo1967]

Thanks Bruce! Yes, that what I imagined, the plug is still good, but no longer readable (on the colder side).

[masracingtd1167]

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