My 383 has about 500-600 miles on it, and now that I have finally (knock on wood) gotten the intake to seal I am hoping to find the time to get the carb jetting closer to optimum. (Using the Lars papers of course)

I just changed the plug the other day so I could see what was going on in the combustion chambers, but I don't really remember much about diagnosing spark plugs.
The color of the electrodes seem pretty good to me, but does the black soot on the outside rim mean that it is running too rich?

2-4-6-8


1-3-5-7

 

Plugs #8 and #3 look to be rich (or just plain cold). Note how the insulator is black on those two where it's tan on others. #2 and #1 look nice -- compare #8 and #3 to them.

I'm not sure if this is an artifact from the photos or what, but it looks like #5 is running lean (or just plain hot). There appear to be blisters on the insulator between 9 o'clock and straight up.

 

Funny this should come up. I just read in my "How to Hot Rod SBC" the correct way to read plugs is immediately after a WOT run with as little idle time as possible. They said the most ideal place is at a drag strip where you can run the quarter and immediately shut it down.

 

If that's when/how you care about how your motor is running, that would be a good idea. When I raced motorcycles that's about how I did it.

 

It looks like you're okay or pretty close on 2,4, 1, and 7. Six is marginal. It looks like your heat range needs to go up by one on 8 and 3. I'd be concerned about 5 as a possible detonation issue based upon the anomaly on the insulator. If it's just a photo issue then I'd say 5 looks good to just a tad hot based upon the ground coloring. It looks like you're dealing only with a fuel issue and not an oil issue. But it's really hard to tell a lot from just photos.

It really depends on what the circumstances are of the relatively brief mileage is though. If these plugs represent the tuning and run-in without much normal road use then you may not be looking at anything worthwhile at this point.

Depending on the cam overlap, carb, and intake, you may not be able to effectively deal with deposits that occur if the engine is spending a lot of time in the idle circuit. As long as your cruise and WOT show a clean burn and you have a good, stable idle and you aren't experiencing detonation, I wouldn't get too concerned about it.

 

I'll (politely) disagree a little on #5. To me it looks like light grey ash deposits indicating a slight oil control problem. Valve seals or intake gasket. It is not enough to really worry about.

As for the other plugs it depends on how the car was driven before the plugs were pulled. If they were pulled after a short trip they are entirely normal. If the car had been driven for atleast 20 minutes and not idled excessively I'd say it is a tad rich. Like 1-2 jet sizes, no more.

All in all, the plugs are certainly passable and indicate no major problems.

 

The #5 cylinder was the one that was sucking the most oil when the intake was leaking (I think I have that problem solved now), so this explaination makes sense.

95% of the miles on this car are stop and go city driving and rural cruising, although I can't control the urge to FLOOR IT whenever possible now but those possibilities are often few and far between because of safety and LEO density reasons.

The engine specs are:
Late (one piece rear seal), 4-bolt main, block
Forged, nitrided crank
Forged I-beam rods
AFR 195 heads (68cc chambers)(10.2-1 CR with my pistons)
Probe forged, flat top pistons
Comp Cams XR-270 hyd roller cam
(Dur @ .050 = In 218, Ex 224, LSA= 110 / Lift= In .495, Ex .502 )
Stock distributor with Pertronix Ignitor II and Flamethrower coil
MSD spiral core wires
Weiand Action plus intake
Weiand Team G water pump
2100 stall torque converter
Turbo 400 tranny with Trans-go shift kit

These plugs were only gapped at .035 . After reading some other recent posts about the Pertronix ignition I figured I could safely go with a wider gap, so I went to .045 on the new set.

So I assume my concern over the black deposits on the outer rim of the plugs is not an issue?

Thanks for the help, you guys are great!

 

With slow speed driving the idle circuit is very influential. Try leaning the idle mixture just a hair and I think you'll see the new plugs stay clean.

0.045" gap is fine. Actually 0.035" is fine also.