I pulled this plug from the #6 cylinder of my 455. I see a lot of images online of what is too lean and what is optimal and sometimes they look the same. This looks lean to me but I am far from knowledgeable at reading plugs. My 455 has 1970 E heads, but the carburator is a numbers correct 73 I bought online which I assume is jetted for a 73. Since the jetting is likely set for smog era J heads, would that potentially lead to a lean mixture if flowing through less restrictive E heads?

 

Your compression ratio is the same, the carb should be close. Did you add headers? That will lean out the mixture.

 

I have headers. The CR isn't 8.5:1. Pistons are v-notch shallow dish 30 over and look like stock replacement 1970 pistons.

 

I would prefer to cut off threads and look at porcelain further down then what is visible here. What it shows here is not really lean to me. Timing looks ok by looking at ground strap. Could have more but its really close.

 

It may be a bit on the lean side. It would be interesting to know what air/fuel ratio it operates at most of the time. Sometime the heat range of the spark plug can also affect their appearance.

 

As long as the engine doesn’t buck, miss or jerk at cruising speed,the engine isn’t too lean. Part throttle, the engine isn’t under enough load to hurt anything. Don’t run a engine lean at full throttle, bad things happen!!