My engine is a 512RB with aluminum heads,10.5 compression,RPM intake, Holley 950HP carb and cam is solid flat tappet 578 lift with 250 duration.


Will a colder heat range spark plug help prevent detonation?

If the heat range is to hot & glowing, yes a colder plug MIGHT help, all you can do is try it. your combo sounds like mine, except I went 9.5 on compression for that reason.

At the time I built the engine we had 93 pump gas...but now all I see is lame 91.

A colder heat range plug, especially on pump gas, can and will make the difference in pinging or not
Ignition timing, jetting, compression ratio, camshaft, altitude and fuel quality all play a BIG part in how soon the motor will go into pinging or detonation also
Aluminum heads allow more compression than iron heads do also
Hemi motors with the spark plug located in the center of the combustion chamber make a small difference also A SB Chevy with iron heads at Lake Mead will detonate a lot sooner with every else thing being the same the same as a iron headed hemi motor on the same day with the same fuel
As far as your motor on 92 octane non ethanol pump swill try 34 degrees total timing in Las Vegas to start with using Champion RC9YC or Autolite # 3923 and then go drive it

I have some champion RC12YC in it right now and I think that is too hot of a plug. I havent noticed anything out of the ordinary on the plugs and they are a light shade of tan color at the electrode ends.

Not as good as a shot of 110...

The Edelbrock heads I have came with instructions and I actually read them. They called for a RC12YC. I ran those for years while dealing with detonation. It is a long and boring story but The engine knocks no more since I added thicker head gaskets and colder plugs, a 9 range...

IMO, that plug is one or two steps too hot. Changing to a cooler plug will help, but it may, or may not fix your problem.

What is your cranking cylinder pressure?

A Champion spark plug engineer told me in a telephone conversation about the year 1996 that 9 heat range is about the "correct" Champion heat range for normal street and interstate driving with factory engines in that it is hot enough to prevent most deposits from fouling the gap, but that Chrysler had gone to heat range 12 and sometimes 14 as factory standard installed on non-turbo factory engines because it gave slightly lower HC and CO emissions during the cold start phase of the EPA emissions test.

I later noticed in a Jeep Chiltons manual that spanned many model years that statement to be true - older recommended spark plugs were 9, then they went to 12 on the same NA engines.

On your race engine build 12 Champion heat range would certainly seem too high.

Start with a cold heat range spark plug,
increase it if you get missfires from fouling deposits that do not burn off.
This is safer that starting with a high number "hot" heat range that can cause pre-ignition near wide open throttle and damage a cylinder.

On a V8 not every cylinder needs exactly the same heat range.
Position of neighboring cylinder exhaust valves, coolant passages in block and cylinder head, and intake manifold runner flow balance can affect the optimum heat range.

Running a 160 t stat and overkill on cooling will help also.
A few years back on one of these TV shows a sparkplug engineer was talking about plug heat range controls the cylinder temps.
you might be able to fatten the mixture a step or two and fix the problem.