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Help reading spark plugs

417 Views 10 Replies 4 Participants Last post by  joeedso
New build bbc 496
I need a little help reading the plugs.
I’m using ngk fr5 plugs gapped to .35
Hei distributor. 22 initial and I curved the distributor for 14 mechanical. Total timing 36
It runs real good now but I wasn’t sure if the heat range is optimal. I originally had in a colder plug auto lite ar3933 and it was not great.
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Overall looks good. Total timing looks great. Heat range looks good. Idle circuit could use a little fuel. Hard to see mid range but it does look like it gets a little darker so probably good there. Wide open throttle you need to take a pic down inside at the base of the porcelain.
 

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Discussion Starter · #4 ·
Overall looks good. Total timing looks great. Heat range looks good. Idle circuit could use a little fuel. Hard to see mid range but it does look like it gets a little darker so probably good there. Wide open throttle you need to take a pic down inside at the base of the porcelain.
 

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Discussion Starter · #5 · (Edited)
Thank you guys for the feedback.
I wasn’t sure if I should try the next hotter plug…
Ngk fr4
I’m guessing maybe I’ll order a new fr5 plug in the meantime and cut it open to check the porcelain inside. It’s hard to see down there
 

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Discussion Starter · #6 ·
Overall looks good. Total timing looks great. Heat range looks good. Idle circuit could use a little fuel. Hard to see mid range but it does look like it gets a little darker so probably good there. Wide open throttle you need to take a pic down inside at the base of the porcelain.
Where exactly do you read the midrange and idle circuit on the plug? I'm trying to learn as much as I can. thank you
 

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Where exactly do you read the midrange and idle circuit on the plug? I'm trying to learn as much as I can. thank you
Think of the porcelain from top to bottom in thirds. The top third including the tip is idle circuit. (This area of the porcelain at the top will also show signs of detonation via little “black pepper flakes”. If you seen anything like that, back the timing off and/or add fuel). The middle third is midrange/cruising. The bottom third down to where the porcelain meets metal is wide open throttle.

Now, each of those thirds will have a corresponding fuel ring (or shading). The darker the ring or shading the richer that area of the fuel curve is. That’s why it’s handy to keep a magnifying glass and flashlight in the car at the track. That way you can look down inside the plug after a pass and see what the car did at wide open throttle going down track.

On your plug, the idle portion of the porcelain is very white so i’d richen it up a bit. That will also help with coolant temps at idle.

Side note of fuel rings… A plug with the right temp will self clean the porcelain. And with the ethonal content in the fuel now-a-days and no lead, sometimes the fuel rings dont show up very well so dont go making drastic changes to get the plug to darken up. Just make small changes and see what the car likes.

You’re heat range on the plugs look good. It has a full turn of color but is not showing down the threads.

The total timing is the mark on the strap. You can see the line on the strap right towards the bottom where the strap meets the plug. The more total timing the farther that line is down the strap. A good starting point for timing is to see that line about half way down in the middle of the bend. From there as you add timing the line will get closer and closer to the base of the strap. This is where you’ll find your max timing. All cars are different and some might like it closer to the base than others. This is also why you start shy on timing and work your way up. Once the cadmium is gone off the strap its gone… When you start shy on timing you can watch the line move farther back as the heat eats the cadmium.

Also, the small discoloration at the end of the strap (right above the electrode) is the idle timing mark. Yours looks good. If that area looks really discolored or burnt than you have too much idle timing.

These are just the basics. I’m sure there’s more people with way more info than this.
 

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Discussion Starter · #8 ·
Think of the porcelain from top to bottom in thirds. The top third including the tip is idle circuit. (This area of the porcelain at the top will also show signs of detonation via little “black pepper flakes”. If you seen anything like that, back the timing off and/or add fuel). The middle third is midrange/cruising. The bottom third down to where the porcelain meets metal is wide open throttle.

Now, each of those thirds will have a corresponding fuel ring (or shading). The darker the ring or shading the richer that area of the fuel curve is. That’s why it’s handy to keep a magnifying glass and flashlight in the car at the track. That way you can look down inside the plug after a pass and see what the car did at wide open throttle going down track.

On your plug, the idle portion of the porcelain is very white so i’d richen it up a bit. That will also help with coolant temps at idle.

Side note of fuel rings… A plug with the right temp will self clean the porcelain. And with the ethonal content in the fuel now-a-days and no lead, sometimes the fuel rings dont show up very well so dont go making drastic changes to get the plug to darken up. Just make small changes and see what the car likes.

You’re heat range on the plugs look good. It has a full turn of color but is not showing down the threads.

The total timing is the mark on the strap. You can see the line on the strap right towards the bottom where the strap meets the plug. The more total timing the farther that line is down the strap. A good starting point for timing is to see that line about half way down in the middle of the bend. From there as you add timing the line will get closer and closer to the base of the strap. This is where you’ll find your max timing. All cars are different and some might like it closer to the base than others. This is also why you start shy on timing and work your way up. Once the cadmium is gone off the strap its gone… When you start shy on timing you can watch the line move farther back as the heat eats the cadmium.

Also, the small discoloration at the end of the strap (right above the electrode) is the idle timing mark. Yours looks good. If that area looks really discolored or burnt than you have too much idle timing.

These are just the basics. I’m sure there’s more people with way more info than this.
Thank you very much!
I appreciate all the advice. I’ll report back as soon as I can cut the plug open
 

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Discussion Starter · #10 · (Edited)
here’s pictures of the plug cut open. It deceiving…
It looks pretty white until you cut it open.
I’m guessing it’s running rich at midrange and wide open throttle. I have a BG race demon 1000 cfm 4150 carb. Jetting is 87 primary and 95 secondary
Should I try dropping those to 85/93?

Thank you
 
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