Question about spark plug heat range

[cobra 53]

After doing new valve job, intake to head matching, some head porting and carb adjustment, I am looking for the spark plug heating range.
After a 60 miles nice flush ride on mounten and back roads the outcome is:

AC Cobra 289 NAF - YouTube

Left plug is NGK BPR 6 ES (cyl. 6)
Right plug is NGK BPR 8 ES (cyl. 2)
There is nearly no exhaust soot on side pipe end.

Which plug would be better?


Rico

[bobcowan]

Based on strap color, I would use BPR 8.

[Dwight]

maybe this link will help

sparkplugreading

Dwight

[blykins]

I would use the 6's. You want to show some heat on the first 2-3 threads. The pictures aren't very clear on my notebook, but it looks like you need to pull a few degrees timing out as well.

[RICK LAKE]

cobra 53 Rico before you start playing with different heat ranges on plugs, I would want to know what the A/F ratios are. The valves are not 100% seated yet either. With new parts would run the motor a little rich for 500 miles before getting crazy.
Thing I have learned from spark plugs range changing. If you use antiseize on the threads of the plug they will knock the heat range down 1-2 ranges. Don't have a 100% proof on this but this is from Antiseize themselves a few years back at a national event.
Color reading the plugs is also alot harder if running a multi spark module that gives up to 30 degrees of spark during firing. This work only at lower rpms to the 3,000 range on MSD system. Can't answer for others. Hear that the ICE system is better than MSD. Makes more power.
I not tryed Livewires. They have a capasitor in the boot by the spark plug and this helps may great spark and the wires are not cheap either.
From the pictures, at this time and new parts, stay with the 6's for a little while. Breakin and then recheck. A/F meter is really needed. Rick L

[Tommy]

Reading what these very knowledgeable people wrote makes me feel kind of ignorant. When I had my engine built, I asked the builder to recommend a slightly cool plug just to be sure I had no problems with detonation. When those fouled out after less than a thousand miles, I went one range hotter and have been using them ever since. .... BTW, I've long thought that reading plugs only tells you what was happening in the last few seconds before the engine was shut off (i.e., the low speed cruise through my neighborhood and into my driveway). Was I wrong?

[bobcowan]

Originally Posted by Tommy

BTW, I've long thought that reading plugs only tells you what was happening in the last few seconds before the engine was shut off (i.e., the low speed cruise through my neighborhood and into my driveway). Was I wrong?

That is exactly right, you only really know what went on over the last few minutes. Drag racers will shut the engine down at the end of the run, and then get towed back to the pits. But you can get a pretty good idea of heat range by looking at the strap and the threads.

Also, with modern fuels and oils, reading the plugs doesn't tell you nearly as much as it did in the olden days.

[blykins]

X2 on everything bob said.

Race plugs also help in reading.