Since all the spark plug experts seem to be in here, can someone read these plugs for me? It's a built 383 LT1 that makes around 500hp. It runs fine except for some pinging at high coolant temps, ambient air temp is high, low rpm and high gear.




The plugs are AC R42LTS6s. I am thinking I want to try a colder set of plugs to see if the pinging at high temp goes away. Finding a cross reference from AC Delco to say Autolite or NGK was tough, so based on some forum posts I've seen I decided to buy some Autolite 103s expecting them to be colder but check out the pic below and see what you think. Is it me or do they look the same?



I originally tried the R42LTS6 because it was supposed to be equivalent to the stock LT1 heat range but I don't know if that's true or not.

 

I'm not going to go "Guru, I'm spark plug master" on 'ya.

I think you are running pretty evenly. The burn on the straps is about halfway on all but it looks like a gasket leak on one. The ceramic has a coating.

EDIT: I'd suggest a 2 degree timing retard in the 80-100kPa range.

 

The plug that has an oil coating is the plug that's almost impossible to torque down good with the tools I have (headers in the way). It's probably leaking around the threads. I will need to get a shorty socket to fix that. But good call.

As for the timing that was where I was going to start. Actually I am going to start with a colder plug first and see what it does. The color is supposed to change a little bit closer to the tip of the electrode from what I have recently read. So I want try out a colder plug to see what happens.

No ones seems to know for sure what heat range these AC R42LTS6 plugs are compared to say an Autolite/NGK equivalent. So finding a colder plug has been a bit of a challenge.

EDIT: Any idea why I'm not getting the nice tan color like a stock motor does?

 

It's difficult to compare different brands of spark plugs based on heat range, the crossover charts are "close" but not law. Those plugs do appear to have the same heat range based on tip length but I don't believe that's the whole story.

Timing is determined by the blue line on the sidewire. It should be above the bend for a drag race application.

If you want to read the full throttle AFR you will want to look at the interface between the shell and the insulator (that's way down inside the plug).

The only thing you will learn from the tip of the plug is the idle AFR.

The only plugs that "color" based on AFR are NGKs.

You should also be careful as correct plug reading is very specific. And, once the plugs are read they are garbage. You need a new set to further evaluate operating criteria.