Plug read, opinions needed

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If that was my engine the solution wouldn’t be a smaller carburetor. The solution would be a different cam. Especially if (like the motortrend article above) the engine made a bunch more power with the bigger carb.
 
TT5.9mag said:
If that was my engine the solution wouldn’t be a smaller carburetor. The solution would be a different cam. Especially if (like the motortrend article above) the engine made a bunch more power with the bigger carb.
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Our own drag car has had various cams ranging from 269 to 289 intake duration in it, the longer the intake duration the smaller the carbys had to be to get max power out of it.
 
The big carby always brigade misses the simple point that a smaller carb can change numerous things such as distribution [ A/F ratio for each cyl ], droplet size etc such that the smaller carb could make more power. Bigger carb is not absolute on every engine. Look at the old MP mods to intake manifolds with popsicle sticks to try & fix uneven A/F ratios in the runners. Try a different carb, these mods might not work.
 
Bewy said:
The big carby always brigade misses the simple point that a smaller carb can change numerous things such as distribution [ A/F ratio for each cyl ], droplet size etc such that the smaller carb could make more power. Bigger carb is not absolute on every engine. Look at the old MP mods to intake manifolds with popsicle sticks to try & fix uneven A/F ratios in the runners. Try a different carb, these mods might not work.
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I agree given some circumstances the smaller carb “could” make more power. But in the motortrend article posted, there is proof that the bigger carbs DID make more power. The poor running was a result of poor tuning. 14 wheel hp is a fairly significant gain at ~400whp, I don’t know a lot of guys willing to give that up, if they’re serious. Now the same would be true if a guy had an 850 and a 650 picked up 14whp.
 
I sure am thankful for finally utilizing the ignore feature 100%. It's taken some time to not click on the messages anyway, but I got it licked. It sure makes for some peaceful reading. I highly recommend it.
 
TT5.9mag said:
Doesn’t work for me either now. It says something about website crashing.
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Well its working this morning.
But here's a copy as an attachment. (hopefully)
 

Attachments

  • Shrinker Sparkplug_reading.pdf
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Bewy said:
The big carby always brigade misses the simple point that a smaller carb can change numerous things such as distribution [ A/F ratio for each cyl ], droplet size etc such that the smaller carb could make more power. Bigger carb is not absolute on every engine. Look at the old MP mods to intake manifolds with popsicle sticks to try & fix uneven A/F ratios in the runners. Try a different carb, these mods might not work.
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I didn’t miss anything. I pointed out the MT article was about useless and that Shrinker didn’t say the answer to every distribution/vaporization issue is a smaller carb.
 
Ok I had a little time today so I pulled all of the plugs back out, marked them all in relation to the ground strap (photo below for reference) and screwed them back in. Then I made a cute little drawing to illustrate the direction the open end of the plug is facing. Remember it’s plugs 2,3,7 that have the dark marking near the tip of the ground strap. Can anyone make sense of any of this?
424F36D4-1652-47C2-B843-44115EFF1956.jpeg
9014775B-90DD-4FD2-843E-0D1491047E30.jpeg
 
And @Garrett Ellison early on you asked me to measure the resistance of my plug wires. These are MSD 8.5 super conductor wires. MSD says they should measure about 50ohms/ft. Mine are brand new (about 6 hours run time on the dyno) have no tears or burn throughs and all of them measured between 100-216 ohms depending on length. We can rule that out.
7D7F1AB5-A184-4276-A708-162344F97294.jpeg
 
Rat Bastid said:
I read what LM say too. That just does not square with my experience.

As an example, I have a buddy who got into the weeds on his tune up. We are talking on the phone about and he has a heat range that made no sense to me. I asked him how he came up with that plug and he said he was reading the ground strap for heat range.

I said I can show you that it doesn’t work that way. The next week I met him at the track.

We started with his plugs. I backed him timing from 39 total to 30 total. And the heat mark on the ground strap moved right back to the end.

At 39 he was right at the bend. So I put 42 in it and that moved the heat mark almost to the shell. And it went a bit quicker there.

After that, I showed him how the fuel ring moves. I put 10 sizes bigger main jets in it, and the fuel ring was wider. I could see he was fat when I started so I went 6 sizes smaller from his base line. And the fuel ring narrowed up to just about perfect.

After that, we put everything back to his baseline tune up and went 2 ranges colder on plug. The heat mark on the ground strap didn’t move one iota. I didn’t want to go any hotter on plug because he was already too hot IMO.

I had him look at the plug he was running and the plug two ranges colder. What changed was the burn down the threads on the shell. The colder plug had about 2 threads showing heat. The plug he was using was a bit over 4 threads.

By then we were out of time, but a week later we went back and started out with his baseline tune up and made two passes. Then we went to the colder plugs, pulled fuel out of it and set the timing to 42 and the car picked up .15.

After all that, he stopped looking at the ground wire to set his heat range. He moved quite a ways away so I don’t see him too often any more. I talk to him a couple times a month. He gets paid to do at the track tuning.
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Rat, you are dead on with your heat range explanation.
4 years ago I was out on the salt flats was honored to witness old ISKY himself tuning a fresh 500 cid blown Keith Black Hemi in a fuel roadster. He walked me through his tuning process and he spent most of his time on heat range versus how many threads were burnt on the plug. On that engine he wanted to see 4 threads burnt.
 
TT5.9mag said:
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.
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Provided the cap looks good then you’ve got the ignition covered.
I’m afraid we might be overthinking this whole deal. It’s a big block Chevy. Then I looked at the pictures, because isn’t this an asymmetrical intake port engine with the long and short intake ports that require weird intake tracts like calliope injection? Aren’t these engines known for needing the carburetor jetting staggered to get consistent plug readings?
 
Garrett Ellison said:
Provided the cap looks good then you’ve got the ignition covered.
I’m afraid we might be overthinking this whole deal. It’s a big block Chevy. Then I looked at the pictures, because isn’t this an asymmetrical intake port engine with the long and short intake ports that require weird intake tracts like calliope injection? Aren’t these engines known for needing the carburetor jetting staggered to get consistent plug readings?
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The cap and the rotor look excellent. There was zero misfires. At one point we had it so rich (9:1) that it fuel misfired but that was very early on, like pull number 2. We moved the O2s all over watching afr throughout the day. There was no staggered jetting needed. The boost tends to make the fuel curve very nice and has the same effect on the distribution. Overthinking makes it seem like I am worried about it. I should have explained earlier that I am absolutely thrilled with how this engine performed. It’s just a weird anomaly that I’ve not experienced yet, and I walk around the pits asking guys if I can look at their plugs. It intrigues me. I was seriously hoping (and still am) that someone comes in here and says “hey I’ve seen that and this is what I think it is”.
 
512Stroker said:
Rat, you are dead on with your heat range explanation.
4 years ago I was out on the salt flats was honored to witness old ISKY himself tuning a fresh 500 cid blown Keith Black Hemi in a fuel roadster. He walked me through his tuning process and he spent most of his time on heat range versus how many threads were burnt on the plug. On that engine he wanted to see 4 threads burnt.
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I have always used the two thread rule for heat range. I like to see color in the two top threads of a plug. On all the forced induction stuff I do I try to use as cold of a plug as I can without fouling to add a little margin of saftey.
 
That's excellent that you didn't need to stagger the jetting and everything works as well as it does. But most definitely intriguing though. Do any of the folks who frequent that facility have any input on it?
The only thing that comes to mind right now is that a member here was using very cold marine iridium plugs in what was described as a boosted application that had problems with exhaust charge contamination. Their quote was that the plugs would self clean better and stay clean longer than conventional copper core plugs. It was running an MSD system. If you can find guidance for a safe point of which plug to start with it may be worth it to see if they read any differently.
 
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See Post #87. Which he’s also got a map showing the direction of orientation that the plug gaps face. Im curious if it would make a difference if he were to index the gap so that it faces the roof of the chamber.
 
The amount of knowledge and brainpower in this thread is overwhelming for a peasant like me that's new to plug reading. Pretty incredible.
 
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Garret, I’m lucky to live so close to a world class dyno room. Steve Brule, IMO, is the industry standard when it comes to running a dyno and tuning this junk. I’ve said it before, when he talks I listen. That being said I didn’t want to wear out my welcome, he is extremely busy and had a free day and snuck me on to
the dyno last minute (I was there Saturday night right as they finished shooting engine masters setting up my junk). Throughout the session I asked as many questions as I could, Steve shared his knowledge every single time, he’s a great Dude. I will cut the shells off the plugs and take a few of them down there for him to look at and get his opinion on. But I’ll have my ducks in a row before I do.
 
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