For the sake of moving things along I’ll share a few bits of information.
1) The heat range of a spark plug rarely has an impact on detonation. For this to happen, the spark plug heat range would have to be so far off that the insulator becomes hot enough to ignite the air/fuel mixture. If this was happening the spark plug insulators would show clear signs of overheating.
2) The heat range of a spark plug has no effect on spark energy given the correct application. You simply select a spark plug hot enough to keep the insulator clean of deposits to prevent the spark plug from fouling. Obviously if the spark plug is fouling out spark energy will be reduced.
3) Spark plugs do not add any heat to the combustion process. A hotter plug will retain more heat in the combustion chamber while a colder plug will transfer that heat faster into the spark plug and the heads.
Could Bboy be on to something in regards to heat transfer into the heads? It’s really far fetched and highly unlikely but I did have to think about it for a second
The hotter the burn the higher the combustion temperatures the higher the HP will be. Remember heat is energy and the less heat you transfer from the combustion process into the spark plugs, heads, and piston the greater the energy available to create power. I believe n2xlr8n was alluding to something along these lines.
As more power is made noise tends to increase as you have everything moving in the engine faster, hitting harder, and with more force. My knock threshold map is significantly different at 400 whp on pump fuel vs. 550 whp on race gas. Unfortunately sometimes knock can happen within the window of normal engine noise if the power is high enough or if the engine is “noisy” enough. The highest level of power comes from riding the cusp on detonation and with a good engine and engine management you can ride this line successfully.
Now, the million dollar question is did you reduce power with the colder spark plugs and therefore engine noise was reduced or did you reduce some low level detonation with a colder spark plug due to controlling the temperature of the insulator? Unfortunately that answer will be in the dyno plot when you put your car on the dyno and test it