ceramic headers as cyl temp indicators

[miketyler]

I have now accumulated some run time on my 340. My ceramic coated headers are not the shiny chrome-like finish they used to be. They all have turned to a more flat finishes metallic silver. I did however notice that my number 4 cylinder has retained much of the original chrome-like finish. What could this indicate? I pulled the plugs and the plug from that cylinder looks a little darker than the others. I will need to test and confirm that it is firing but I would be surprised if it isnt because the engine seems too smooth to have a missing cylinder. Any other ideas? Bad plug or lower compression? Should I be concerned?         

[67vertman]

I have had the headers on my 67 convertible ceramic coated (sterling silver) for over eight years with no discoloration, they where coated by Jet-Hot coatings in Arizona. 

In my experience if one header tube is a different color than the rest, that cylinder is running cooler.  It could be that spark plug wire is damaged or shorting out, check it with an Ohms meter.   Also, check the gap on that plug or its ceramic insulator. I had a small crack in one and it was shorting out against the block.

[Chryco Psycho]

if the plug is darker on the "good" pipe it is running cooler , you may be jetted to lean & creating excessive heat in most of the cylinders

[miketyler]

you know, thats what I had thought but it didnt make sense. I mean, I am running a dual plane manifold. If it were a lean condition, wouldnt all the cylinders on that side be running hot?

[Chryco Psycho]

not nessisarily , # 4 pipe may have less restriction or the intake could be unevenly distributing the fuel allowing #4 to run slightly cooler

[67Vette427]

Did you use these headers on initial break in? New motors get real hot when new. If they were used you won't get them shiny again.

[dodgetkboy78]

Yeah, what he said.
The little piece of paper that comes with the headers says not to run them on a new engine, but use manifolds or something until it is broke in.
Sounds like you are running lean, or have your timing retarded.

[miketyler]

engine was already broke in, only had a new cam and timing gears installed (and a helluva lot of prettying up). Timing is set stock 2.5 BTDC at idle, with the vacuum advance disconnected. 

[dodgetkboy78]

Well................what is it at full advance?
Initial don't really cut it.

[miketyler]

I dont know - I always thought for stock confguration, you set it at idle, VA unplugged. Once set it was good across the full range of RPM. Was there another timing setting that I missed?

[Grancoupe]

you want to bring the motor up to about 3000 RPM with the timing light on the balancer. Record the timing. That will give you the full advance. Are your valves adjustable? Maybe your exhaust valve  isn't set to open fully?

[miketyler]

its a stock 340 with hydraulic lifters, stock cam. I dont think they are adjustable.