The T/A is running almost perfect but still needs a little tweeking. My ET is down to a 12.78 at 109.49 mph with a 60 foot of 2.02. The 2,8,1,7 plugs look awesome! The 4,6,3,5 plugs look a bit rich. It's a 6 pack set up and I'm thinking the distribution the manifold gives is what's giving the cylinders different amounts of fuel. Or is it one of the carbs doing it? The question is........... I'm running NGK5672A-8 plugs and was thinking about putting a hotter plug in the 4 holes that seem richer. Will this help anything or is mixing plugs tabboo?

When you say the plugs look good on some and fat on others is this based on cruise plug readings or on wide open throttle plug readings? If at cruise try opening the idle air bleed .003 to .006 on the bleed in the center carb. that feeds those cylinders. I would tell you which side but I don't have a 340 six pak intake to look at, sorry. To answer the main question you can run one step hotter plug to mask the problem and probally get away with it, but if the WOT is lean then your taking a chance of causing those four cylinders to go into detonation Let us know what you end up doing to solve that please

I run the coldest plug that don't foul.
like Cab said you can run a hoter plug and mask the problum but it might go into detonation.

Listen to Cab. He knows what he is talking about. He helped me with my spark plug problems.

Ok,,,, I'll play with the carbs some more and see what comes up. And to answer the question of when the plugs are checked,,, It is after a pass.

are these new plugs your trying to read? if not your probably wasting your time. and whats telling you some are rich and some not? how are you reading them?

whats your compression?
-5672a-8 12-13.5 compression
if lower than that go 1 step hotter on your plug.5672a-7 9-11.5 compression

Yes they are new when read, just after a pass. I'm reading them by the color around the porcelin and by the electrode. It's an eddy head 416 stroker with 12:1 compression.