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Discussion Starter #1
Alright so I've been ALL OVER the internet trying to find a good answer to this and I really haven't come up with much. How do you find your secondary jet size (with max HP in mind) on a traditional Vacuum Secondary Holley 4 Barrel without an AFR gauge or a drag strip to evaluate E.T.'s and MPH?

I've read about basically throwing in a fresh plug on a cylinder of your choice, hammering it through the gears, then killing the engine immediately and coasting to a spot to pull the plug so you can hack off the threaded portion and read the "mixture ring" (ideally about 1/8 to 3/16 wide) at the base of the porcelain for your WOT jetting.. this is the ONLY method I could find.

I'm wondering if anyone on here has any suggestions or if they can elaborate more on the "mixture ring" (darkness of ring, color, width, etc.) and the best way to run a motor to get this "mixture ring".

I have pulled one of the plugs that has roughly 50 miles on it and hacked off the threaded portion just to evaluate the porcelain for main jetting and cruise which looks pretty good, but the mixture ring at the base of the porcelain is THICK and very dark. Like covering the bottom 2/3 of the porcelain thick and dark brown on the verge of black/sooty.

Now I know it probably doesn't matter because this plug was pulled from an engine that is driven around town, and it was pulled from a motor that had to cruise around 2000 to 3000 rpm until I idled it into the garage and killed it.

Is this normal for the "mixture ring" to look like this when pulled from a motor after cruising and in town driving?

More importantly though, I'm mainly concerned on how to check the plug porcelain for SECONDARY JETTING for MAX HP and what's the best method to go about this without the AFR gauge or a drag strip??


Thanks in advance guys and I can't wait to see what y'all have to say.
 

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You have pretty much answered your own question, without either wideband readouts, drag strip testing, or chassis dyno testing, all you can do is get close....there are no other ways that I know of.

Engine dyno testing can also be used, but best jetting on the dyno is frequently not the best jetting once the engine is actually installed and running in a vehicle. Plug reading, done correctly with no idle or cruise time, still won't get you as close at strip MPH or chassis dyno.
 

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You really need a place you can run at full throttle and shut off the ignition and coast to a stop do not idle or drive the car !!! Pull the plugs and put them in your pocket for later readings and install new plugs and drive your car !, when you get to a spot maybe the pits or home take the plugs you pulled after your run and cut and read them. The deepest point in the threaded area of the porcelain is what you read not the tip! It may take a special plug flashlight with a magnifying glass to see your ring color its very hard with just your eyes to see it!!! On a normally aspirated engine light gray to tan color ring depending on your fuel used will be a good indication your jetted close or even a lite brown (again depending on fuel) may be good.

Jester
 

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Discussion Starter #4
You really need a place you can run at full throttle and shut off the ignition and coast to a stop do not idle or drive the car !!! Pull the plugs and put them in your pocket for later readings and install new plugs and drive your car !, when you get to a spot maybe the pits or home take the plugs you pulled after your run and cut and read them. The deepest point in the threaded area of the porcelain is what you read not the tip! It may take a special plug flashlight with a magnifying glass to see your ring color its very hard with just your eyes to see it!!! On a normally aspirated engine light gray to tan color ring depending on your fuel used will be a good indication your jetted close or even a lite brown (again depending on fuel) may be good.

Jester


Thanks jester!!


That's what I've been reading about but it seems a little fuzzy to me.


So you're just looking for the color of the base ring not the thickness??


I've read that you want a nice chocolate brown ring about 1/8" thick.. is that just a different method or does the width not madder?


I have a nice empty stretch of road where I was going to take 3 fresh plugs, and a range of 3 jet sizes for the secondary's so I can get a nice WOT pull on all three plugs (with a different jet) so I could bring them back to the garage later and check for the base ring and determine which is the best secondary jet.
 

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Discussion Starter #5
You have pretty much answered your own question, without either wideband readouts, drag strip testing, or chassis dyno testing, all you can do is get close....there are no other ways that I know of.

Engine dyno testing can also be used, but best jetting on the dyno is frequently not the best jetting once the engine is actually installed and running in a vehicle. Plug reading, done correctly with no idle or cruise time, still won't get you as close at strip MPH or chassis dyno.


Lol damn! You know I really wish I had a chance to tune it at the strip, but the closest track is over an hour away and I'm not quite confident in my cars mechanical ability to run it at the track just yet. I don't want to go out there and embarrass myself.. so until then I'm gonna screw around with my tuning on the streets and in the garage so when I FINALLY get to the strip I have a good baseline.
 

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to expand on what Chris pointed out,sorry, but you will need to retune all over again when close if thr plugs were not indexed,,, That alone is a couple horse power,,,
 

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Discussion Starter #8
to expand on what Chris pointed out,sorry, but you will need to retune all over again when close if thr plugs were not indexed,,, That alone is a couple horse power,,,


What exactly do you mean by "indexed"?


Do you mean by using indexing washers to get the spark plug gap facing directly into the combustion chamber?
 

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"So you're just looking for the color of the base ring not the thickness??"

Yes:thumbup:

Question:
"I've read that you want a nice chocolate brown ring about 1/8" thick.. is that just a different method or does the width not madder?"
Answer:
The old fuels (like high octane leaded) would leave a thicker ring but the new fuels non leaded and others sometimes will not leave any ring!

You can pull your headers and get an idea from the first 8 inches into the primary tubes if the jetting is good with the rest of the exhaust disconnected! If the pipe is clean your too lean if black your too rich a nice gray to brown is about right but that is not an exact science its what we did at the track as temperatures fluctuated from a hot day to a cool evening!!

EDIT:And we had room to pull the headers LOL and you can look into the head exhaust port for a gray to tan color!

Jester
 

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Wow that is some good info posted above for tuning and looking at spark plugs. I have not to some degree been that detailed on my secondary side of things but I will be trying some of the things mentioned above. I need to get one of those magnifying glasses so I can really check things. I to am in the boat of getting close but that is been good for me all these years as I don't race mine and never take to the track and pretty much just tune for overall performance and good cruising manners and as clean as an idle I can get. Seems like your coming along pretty good.
 

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You need to check all plugs not just a few especially on a drag car!! if flow through the intake is not exactly the same in all ports depending on intake design and slight cylinder differences or poor designed primary exhaust scavanging you may have a lean or over rich condition on 1 or 2 cylinders !! And that would be disaster! Its better to have a few cylinders running a little rich at full throttle then 1 or 2 running lean! On 360 open plenum intakes or tunnel rams , or tri power or dual quad or any multy carb intake for drag you may even need to stagger jet the carb or carbs because the carbs feed specific ports directly!
On 8 cylinder 180 plenum intakes its like running 2 4 cylinder engines and stagger jetting is sometimes needed! this is not for stock street engines its for drag cars and sustained full throttle running its really nothing for a novice to worry about and most builders never heard of that, somtimes one side of a carb will be jetted different then the other or even 1 jet different in the metering block!

Jester
 

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Discussion Starter #13
You need to check all plugs not just a few especially on a drag car!! if flow through the intake is not exactly the same in all ports depending on intake design and slight cylinder differences or poor designed primary exhaust scavanging you may have a lean or over rich condition on 1 or 2 cylinders !! And that would be disaster! Its better to have a few cylinders running a little rich at full throttle then 1 or 2 running lean! On 360 open plenum intakes or tunnel rams , or tri power or dual quad or any multy carb intake for drag you may even need to stagger jet the carb or carbs because the carbs feed specific ports directly!
On 8 cylinder 180 plenum intakes its like running 2 4 cylinder engines and stagger jetting is sometimes needed! this is not for stock street engines its for drag cars and sustained full throttle running its really nothing for a novice to worry about and most builders never heard of that, somtimes one side of a carb will be jetted different then the other or even 1 jet different in the metering block!

Jester


Hahaha If I had the room and patience to pull my headers and check I would!


I think I'll go with the plug reading method you have expanded on, as that's the most reasonable.


I do plan on checking ALL plugs, after I get a good baseline on one cylinder :)


I'm not good at leaving **** alone anyway lol.
 

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. You want the car running/driving/cruising perfectly on the primaries first with the insulator staying a light tan, before worrying about the secondaries...
 
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