Plug read, opinions needed

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TT5.9mag

Two atmospheres are better than one
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Guys, I spent all day on the dyno yesterday. 26 pulls total, lots of carb tuning. Not a mopar so don’t hate me. This is the big block Chevy for my boat, twin turbo, pump gas, low boost, blow through set up. I know how to read a plug, but I’m seeing something I’m not familiar with. On the very tip of the ground strap on 3 plugs I have a color change similar to the timing mark at the base, but at the end. What is the color change an indicator of?
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Which 3 cylinders? Did you test with EGT’s? I can say I’ve never seen that before and wouldn’t want to venture a guess. I probably be dead wrong.

Just because I’m curious what do you have for an ignition and timing???
 
This engine has 31 degrees in it at 7psi. The timing mark is around the bend near the plug base right were it should be. We swept the timing from 22 to 34 degrees. I promise you it does not need more.
 
Rat Bastid said:
Which 3 cylinders? Did you test with EGT’s? I can say I’ve never seen that before and wouldn’t want to venture a guess. I probably be dead wrong.

Just because I’m curious what do you have for an ignition and timing???
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Cylinders 2,7,3
On the dyno Brule uses a digital MSD 7 box and the engine has an MSD pro billet distributor locked out. Final timing was 31 degrees. We did not have individual egt probes on it.
 
I see it on them all, it's just more on the very tip end on the others. I think it needs a hotter plug.
 
Close up of plug #1. Has a slightly dark coloration right at the end but certainly not as pronounced as the 3 mentioned above.
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Were the spark plugs indexed? Maybe the ground strap is in a different part of the chamber in those 3 cylinders.
 
That grey is most likely exhaust gas. Restrictive exhaust or too much overlap?

To be honest in my opinion that second one is very good. What the spark plug tells you is the mixture AFR and quality of the mixture at time of ignition. Just because you give the cylinder a certain AFR doesn't mean that's what it is at the plug at time of ignition. Timing mark is myth.

Good to see people actually reading plugs instead of just an O2 gauge.
 
What do the rest of the plugs look like? Do you care to post some pics of the plugs that are burning the cleanest? It may be temperature range, but if the other cylinders are right on target, then hotter plugs may not be too good in those cylinders. Maybe check resistance on those four plug wires to see if anything’s off compared to the rest of them. If the plugs are on the cold side, it may be showing those cylinders are going a little rich during the pull. I know that’s probably unlikely in a boosted application, but that is pretty odd.
 
TT5.9mag said:
Guys, I spent all day on the dyno yesterday. 26 pulls total, lots of carb tuning. Not a mopar so don’t hate me. This is the big block Chevy for my boat, twin turbo, pump gas, low boost, blow through set up. I know how to read a plug, but I’m seeing something I’m not familiar with. On the very tip of the ground strap on 3 plugs I have a color change similar to the timing mark at the base, but at the end. What is the color change an indicator of?
View attachment 1715978328 View attachment 1715978329 View attachment 1715978330 View attachment 1715978331
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Not looking at the picture but answering your question the total timing will be the Mark or color change that stops closest to the base ring while the Mark just on the other side of the bend of the tab closest to the electro tip will be the initial timing mark. Typically you will read they want those to be right about even on each side of the bend...everything's unique to the build of course... some people like to see it all the way down to the base Circle , as in ..a lot of total timing but you'll realize or find out how much time it really likes that's my advice and what I know.
 
MOPAROFFICIAL said:
Not looking at the picture but answering your question the total timing will be the Mark or color change that stops closest to the base ring while the Mark just on the other side of the bend of the tab closest to the electro tip will be the initial timing mark. Typically you will read they want those to be right about even on each side of the bend...everything's unique to the build of course... some people like to see it all the way down to the base Circle , as in ..a lot of total timing but you'll realize or find out how much time it really likes that's my advice and what I know.
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This distributor is locked out at 31. Initial and total are one and the same.
 
Garrett Ellison said:
What do the rest of the plugs look like? Do you care to post some pics of the plugs that are burning the cleanest? It may be temperature range, but if the other cylinders are right on target, then hotter plugs may not be too good in those cylinders. Maybe check resistance on those four plug wires to see if anything’s off compared to the rest of them. If the plugs are on the cold side, it may be showing those cylinders are going a little rich during the pull. I know that’s probably unlikely in a boosted application, but that is pretty odd.
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I’ll show anything you’d like to see I have nothing to hide or keep secret especially if we can all learn something. The two close up pics above are good a representation of all of the plugs that came out of this engine. 3 of them having a very similar dark tip and 5 of them looking like plug #1.
 
Hysteric said:
That grey is most likely exhaust gas. Restrictive exhaust or too much overlap?

To be honest in my opinion that second one is very good. What the spark plug tells you is the mixture AFR and quality of the mixture at time of ignition. Just because you give the cylinder a certain AFR doesn't mean that's what it is at the plug at time of ignition. Timing mark is myth.

Good to see people actually reading plugs instead of just an O2 gauge.
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This is a marine application and the overlap is about as high as I can run with the exhaust outlets under water. The cam is a comp extreme marine 284 hydraulic roller. 230/236 @050 .557 lift. Your restricted exhaust suggestion has me thinking. They are an old set of Gale banks water cooled log style headers and definitely are more restrictive than a set of headers. But turbos make backpressure so any exhaust with turbos at the end could be considered restrictive.
 
Sterling said:
Were the spark plugs indexed? Maybe the ground strap is in a different part of the chamber in those 3 cylinders.
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Plugs were not indexed. Just screwed right in and run. Good thought.
 
Hysteric said:
That grey is most likely exhaust gas. Restrictive exhaust or too much overlap?

To be honest in my opinion that second one is very good. What the spark plug tells you is the mixture AFR and quality of the mixture at time of ignition. Just because you give the cylinder a certain AFR doesn't mean that's what it is at the plug at time of ignition. Timing mark is myth.

Good to see people actually reading plugs instead of just an O2 gauge.
Click to expand...
The fuel curve was surprisingly flat. After lots of carb changes we were able to get it to cruise (30-50% load 3500rpm) at around 12.9 and wot was flat, varying only a tenth or two afr points, 11.4- 11.6 from 3500-6100 where we shut it off.
 
Only pull I have a picture of the printout on, we actually dialed the afr in a little better than this run on the next few. Power didn’t change much at all.
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HSDemon said:
Check this out:
Tips - Reading Spark Plugs - Ken's Auto Machine Shop
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Thanks. Same article Rusty posted above. I have read that, While it’s certainly a possibility, I don’t agree with some of the points in that article about fueling so it makes me question the validity of the other information in it. I’m open to being wrong, hell it happens a lot, just not what I have been taught over the years. The best plug read article/video is from Steve Morris imo. I’ll find it and post it here.
 
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