Help picking spark plugs.

[Dutch Rutter]

Looks wicked lean to me but i'm just a schlub on the innerwebs.

I forward the motion that you are also wicked under-carbed. 1405 is a 500. That's not enough
Maybe for a stock 305...


Think 670 Street Avenger and be like word up.

I was also thinking lean but I admittedly dont know enough to say 100% positively. I do like the idea of going to a street avenger, have also been eyeballing those quick fuel carbs pretty hard. I'll start by trying to fatten this thing up and see what that does for it. The pressure regulator is working right and holding at 4.5 psi at idle so that's well and good for the eddy. Guess I'll be ordering one of their "calibration" kits and start changing some needles and what nots.

Thanks for the insight rusty I really appreciate your expertise

Edit: double checked, the 1405 is a 600cfm still might be a little on the undercarbed side tho.

 

[Rusty Nail]

hay dude youre right. i thought a 1405 was 500...1406 us a 650?
those plugs are freaking beautiful man what are we missing?

I'm looking at what appears to be ash deposit on the threads...?

 

[Dutch Rutter]

Both 1405 and 1406 are 600 cfms but the 1405 is their "performance" jetted with a manual choke while the 1406 is their more fuel conservative jetting and an electric choke.

I opted for the 1405 thinking it would perform better with the mild build and added the electric choke to it. Probably should have just jumped ship and got a holley.

The dark on the threads I'm thinking is more oil or unburnt fuel from running those wrong plugs before. I'm more used to seeing a crispy toast color to things but these have what looks like a grey soot on them. Granted they only have 180 miles on them, but I thought for sure I would be able to get some color on them. My other thought is that I might be at too cool of a plug these being a 7 out of 11 and I should go up to a 6 or even a 5.

It is also very possible this carb is too lean, the calibration kit would be able to fix that up. It'll be here the 31st.

edit: Could also be that I'm overlooking something right in front of my face. I did check for intake leaks a while back and didn't find anything but I will check again tomorrow morning just to be sure there isn't something leaning it out. I am running premium pump gas maybe I need to try regular but I figured better off with premium for better spark knock protection.

 

[Paladin]

Probably should have just jumped ship and got a holley.

Amen!

 

[gotyourgoat]

Update on this. Still have 600 miles until oil change time but I went ahead and checked the spark plugs anyway. Here is number 2, 4 and 6. All of the others looked the same. I'm not sure about the white soot look so I'm thinking I need more miles on them before making a decision. The new plugs cleaned up the down low pull and all but removed an annoying off idle stumble I was chasing.

As for the engine itself it's pretty mild. 355, with stock like pistons, a mild torquey cam, and 64cc chamber pro comp heads with 190cc intake runners that have been fully gone over with new studs, valve seats, valves etc. An performer RPM intake and an edelbrock 1405 performer carb more details here if needed.
Https://www.gmsquarebody.com/threads/working-over-a-motor.25526/

For the big picture people the last two photos are why I started looking at my plugs. Only saw this on #6 and #7 I did a compression test, fearing the worst, and found all cylinders to be 168-171 without any leaking down quickly. So I chalked it up to misfiring or maybe my rings gaping got lined up? I really have no idea. Probably nothing to worry about since it's running great.

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These are what you consider dirty plugs?

Wow. I drive garbage.

 

[Rusty Nail]

^lmao.

I woke up with a new attitude today.

Perhaps you secretly long to be impressed. Although you want to give as good as you get, we can act impulsively if we perceive that we're handing out more than we're receiving.
talkin about 30-40 year old trucks, it's easy to do...

Too much measuring leads to competition don't you agree? This analytical approach may be how your passion does you a disservice.
I believe it happens to me,,

Only a thought.

It'll go faster if you put a bigger carburetor on it though lmao..

President Theodore Roosevelt said, “Comparison is the thief of joy.”

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[Dutch Rutter]

I'd be happy to move up to a bigger carb except for then I would be starting over with tuning. Plus spending the cash for a nice new bigger air and gas mixer.

My ole man says these plugs look good. He's an old shade tree mechanic and has taught me alot however, alot of times we don't see eye to eye 100%. My instinct tells me these are on the lean side.

But I agree I always over analyze everything mainly because I worry about screwing this poor thing up. But I'm tracking, I'll get more miles on it and see what I get. Sheet I might even experiment some with that damned jetting kit. We'll see.

 

[SirRobyn0]

I'd be happy to move up to a bigger carb except for then I would be starting over with tuning. Plus spending the cash for a nice new bigger air and gas mixer.

My ole man says these plugs look good. He's an old shade tree mechanic and has taught me alot however, alot of times we don't see eye to eye 100%. My instinct tells me these are on the lean side.

But I agree I always over analyze everything mainly because I worry about screwing this poor thing up. But I'm tracking, I'll get more miles on it and see what I get. Sheet I might even experiment some with that damned jetting kit. We'll see.

I kind of have trouble with over analyzing to, so don't worry about it. As for the carb, I'd be like you, want to stay with what you have because it is tuned. For me I'm Johnny anal about how my vehicles run, this includes cold starts. So on my square and other carbureted rigs I have to have them start cold with one pump of gas, and be able drive right away without any hesitation or stumbling. So I spent quite a bit of time (a few weeks worth of cold starts) tuning the choke settings, and fast idle speed. Also had to get the heat riser working.

Enough of me rattling on about me. Your plugs. So back in the day the ideal look was a light tan, now todays fuels burn much cleaner so a white plug, with minimal tan is perfectly fine where as that might have been a little lean. I would say your plugs are a little dirty and you could probably up the heat range one step, but if these your current ones don't foul I don't see a problem with continuing to use them.

 

[MikeB]

my thought was:

Ngk is for Honda
Autolite is for Ford
Champion is for Chrysler

That's sorta like using only GM oil and GM windshield wiper fluid in Chevrolets!

Engines don't know what brand plugs are in them, assuming they are the proper length and heat range. I mean it's not like Chevy engines require some magic AC plugs with a patented heat range. Not only that, but the OP's heads are aftermarket. And below the combustion chamber there's nothing but a piston going up and down.

On another note, platinum plugs are a step above the old school plugs because the precious metal electrodes will hold their gap longer. And that's the only advantage.

 

[bucket]

That's sorta like using only GM oil and GM windshield wiper fluid in Chevrolets!

Engines don't know what brand plugs are in them, assuming they are the proper length and heat range. I mean it's not like Chevy engines require some magic AC plugs with a patented heat range. Not only that, but the OP's heads are aftermarket. And below the combustion chamber there's nothing but a piston going up and down.

On another note, platinum plugs are a step above the old school plugs because the precious metal electrodes will hold their gap longer. And that's the only advantage.

I don't know the science behind it, but Bosch Platinum plugs do not last very long when paired with GM ignition systems. I've seen the results many many times.

 

[SirRobyn0]

my thought was:

Ngk is for Honda
Autolite is for Ford
Champion is for Chrysler

That's sorta like using only GM oil and GM windshield wiper fluid in Chevrolets!

On another note, platinum plugs are a step above the old school plugs because the precious metal electrodes will hold their gap longer. And that's the only advantage.

That is an old school theory that a lot of folks have subscribed to, it comes from the days that autolite made motorcraft plugs, and Chrysler products rolled out of the factory with champion plugs, and gm with ac delco. Because of that I do like to run ac delco in my gms, but yes I'm sure other plugs would work just as well. On a side note platinum plugs will foul out easier than a resistor plug.

I don't know the science behind it, but Bosch Platinum plugs do not last very long when paired with GM ignition systems. I've seen the results many many times.

I have seen this to at the shop. Honestly I can't think of an American car that like Bosch platinum. It's to bad because I really like thier wiper blades!

 

[idahovette]

Old school theory or not, I have always run ACs in everything I have. Never let me down. Of course I only have Chevys so that makes it easier!!

 

[Rusty Nail]

That's sorta like using only GM oil and GM windshield wiper fluid in Chevrolets!

Engines don't know what brand plugs are in them, assuming they are the proper length and heat range. I mean it's not like Chevy engines require some magic AC plugs with a patented heat range. Not only that, but the OP's heads are aftermarket. And below the combustion chamber there's nothing but a piston going up and down.

On another note, platinum plugs are a step above the old school plugs because the precious metal electrodes will hold their gap longer. And that's the only advantage.

Hey the less an engine knows, the better off it is where I come from. That's kind of how I got HERE, one could say.
Thirty, forty years later sure somebody made "improved" trucks - if you wanna call it that you can but I don't feel that way.
They aint broke and dont need fixin if ya ask me, no different than the spark plugs.
Ya know, there used to be a thing called brand loyalty where I come from and some of my friends share a strange sense of pride that only grows more rare, like our trucks But hay, whatever. If you want to spend time and money chasing whatever is newest and latest or improved, i'll help defend your right to do so if you think it will make you happy...we're still only splitting hairs.

More power to ya .

Where I come from @MikeB , they call that the pursuit of happiness - Sounds like they call it something else over there...

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[Poppy 87]

I use AC Delco or NGK exclusively. I wouldn't put autolite into any engine I own, including my lawn mower

 

[MikeB]

For those who have problems with plugs lasting a long time: How do they fail? Eroded electrodes, oil-fouled?

In my experience, Bosch platinum plugs (single electrode) last a long time with GM HEI distributors --either stock or with MSD module & coil. I have no idea why they wouldn't work for any Chevy ignition. I'm currently running basic NGK plugs in a 355 with GM Vortec heads, and they also work fine. And their plated bodies don't rust like AC and Autolite.

Also, it's worth mentioning again that there are different "reach" plugs, which is the length of the threaded portion. Also, either tapered or gaskets seats. Not a problem when using the exact AC plug specified for a stock engine, but can be a problem with aftermarket heads.