Appreciate some input on spark plug reading

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Demonx2

Demonx2

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The plugs are on my avatar Demon - 408, 10.5 CR, 251/[email protected] SFT, 850 DP, Super Victor, MSD 6, Autolite 3924 plugs, 5000 stall conv, 4.10 axle, footbrake car. Engine runs ~34 degrees total timing and given the flash stall of 5000 rpm, it's certainly all in when the car leaves! Best so far is 11.10 @ 119+. Hopefully that covers the basics.

New to Florida and running at the Gainesville track. Haven't really jetted it any differently than back in Michigan but thought I'd ask for some experienced plug readers input. To me, the car can feel a bit sluggish pulling on the big end and I'm wondering if a couple degrees more timing might be worth a try as jetting (at least in Michigan) did not impact the mph at all. Note this "sluggish" feeling on the big end has not changed since moving south.

Pulled the plugs and they all look basically the same. The ground strap is clean until about 1/8" from where it connects to the body. I cannot really see any coloring on the insulator but I have not had a plug cut (but I doubt that would change the reading). This is all consistent from my experiences back in Michigan.

Here's some shots of the plugs. Tried to show the ground strap coloring but photos are a bit tricky. To me, they look just about right but thought I'd ask.
#1:
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#3:
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I could post others but they look identical - no difference from front to back or LH versus RH side of engine.

Thx for any pearls of wisdom!! (And nope... not moving back north!! Lol)
 
Several questions:

Can you cut the threads off and show us the porcelain?

What is the gap you're running on these plugs?

Was it breaking up at all the big end or did it just lose steam?

What fuel pressure are you running and what pump do you have?

Edit: Lastly, where are your floats set at?
 
Are you running pump gas? Pump gas is really sooty so that might explain the sooty color. If you're running race gas then I'd say you're too rich. You kind of need to know the fuel is in order to read the plugs. In the same engine gas will look different than pump gas which looks different from race gas.
 
One of the pics looks like there is peppering on the porcelain. Might just be the pic. What fuel do you run? Definitely cut the shell off a plug and look at the fuel ring. Should be about .100-.110 up from the base. And your timing looks 2-3 degrees soft for what I would consider optimal. You want the ground strap tanned almost all the way to the thread if you’re running it on the edge. Most don’t like doing that though.
 
I would first try an NGK plug and a 750 DP and see if it picks up the top end.
 
Just Send It said:
Several questions:

Can you cut the threads off and show us the porcelain?

What is the gap you're running on these plugs?

Was it breaking up at all the big end or did it just lose steam?

What fuel pressure are you running and what pump do you have?

Edit: Lastly, where are your floats set at?
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Answers to your and the other questions:

1. Short of a hacksaw, I don't have a lathe or anything to cut off threads. I can say the porcelain is pretty much uncovered but will further inspect.

2. I run 0.035" gap and they all measured consistent at that.

3. It does not break up - I just think it could pull harder as it feels a bit flat to me. It runs 7.01 @ 96 in the 1/8 and 11.1x in the quarter with typical 60' times of 1.52 (best of 1.49).

4. The floats are set so fuel is dribbling out with the bowl plugs pulled. I run a constant 6 psi the entire length of the track (has a fuel pressure gauge).

⛽️ The car runs 93 octane pump fuel. When driven on the street (which it does see more than most would think) it does soot up the plugs from putt-putting around. But pulling the plugs after 1 pass and they immediately look like this i.e. they clean right up.

I looked hard to see about peppering which is why I pulled the plugs before I added any spark. I am familiar with that but do not see any evidence looking very closely. One of the pics does make it look like it though (but it is just the pic).

My initial thought is I think there's another 1-2 degrees I could throw at it just to see if the mph picks up. With no peppering and the ground strap coloring, I think it still looks like that nay be OK.

Thx to all for your input and responses!!
 
Here is what i see your tune looks fairly good it's hard to tell idle with pump fuel it nearly always looks rich . Maybe a tad rich on idle , cruise looks good i can't see wide open thottle fuel ring , timing looks good . the heat range could be 1 or 2 numbers cooler maybe . i'm no pro tuner just love learning .
 
He is another piece- take it or leave it.

Not sure of the temps in FLA (lucky b you) but because they don’t deal with snow like we do- tracks run year round. But temps are cooler and air is more dense. My cars here in CT are still dealing with much cooler air than in summer. I leave alone and as they seem to be adjusted for summer air. I hope that make sense. I’d not want to melt down a piston top due to lack of fuel. A larger carb (more jet) will help your issue. See is their are any other transplants where your racing and ask them. They have already been thru this.
Good luck and keep us posted!
Syleng1
 
On pump gas that plug looks very good for what I can see.

As AndyF said above, pump gas looks sooty like that. You might be able to clean up the spot on the shell a little more but that’s probably going to take an emulsion change. And at that you probably won’t see .001 for all the work.

You can cut the shell off with a hack saw. It’s worth it to get a good look at the base of the plug.
 
Do you have a 4” angle grinder? With a cutoff wheel cut the crimp. Red line and pull the porcelain out. This is what you’ll be left with. Don’t compare yours to this though.

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7BF1A9DE-2BC2-4ACE-B1F2-ADCA687D4413.jpeg
 
Fuel pressure does not mean fuel in the bowl. Don’t think fuel is your problem though. An issue I ran into is the rotor being too high in relation to the cap terminal. So the arc marks were up not out towards the terminal face. It would flutter a bit at higher rpm’s. Very subtle. Filed the bottom of the rotor and no more flutter. “Soft at the top” could just be air quality. In air flow restricted engines, (which almost all stroked LA’s are) air quality really hurts. I can see 3-4 tenths change just due to air quality and I have chased my tail trying to get it back by tuning…..never been successful. What heads?
 
5/8" hole saw with the drill bit removed. Takes about 10 seconds to cleanly remove the threads.

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If you're running at Gainesville it will get very humid during the summer months. You'll need to adjust accordingly. I ran there back in the '78-81 time frame when I stationed in Jacksonville with the Navy.
 
furrystump said:
Fuel pressure does not mean fuel in the bowl. Don’t think fuel is your problem though. An issue I ran into is the rotor being too high in relation to the cap terminal. So the arc marks were up not out towards the terminal face. It would flutter a bit at higher rpm’s. Very subtle. Filed the bottom of the rotor and no more flutter. “Soft at the top” could just be air quality. In air flow restricted engines, (which almost all stroked LA’s are) air quality really hurts. I can see 3-4 tenths change just due to air quality and I have chased my tail trying to get it back by tuning…..never been successful. What heads?
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I should have listed the heads right up front - my bad. They are simple Eddie RPM with somewhat mild bowl porting. So I believe these to be the limiting factor for my combo.
It's not that I'm not happy with it. But like everyone, I want to get all there is out of what I've got!
 
Les Gibson said:
If you're running at Gainesville it will get very humid during the summer months. You'll need to adjust accordingly. I ran there back in the '78-81 time frame when I stationed in Jacksonville with the Navy.
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Yes - I figure it will need jetted down as temps rise. But this past Sunday was 87 deg so not exactly great air. I didn't catch the water grains but the DA was just under 2000.

And Gainesville actually does not schedule bracket racing in July and August due to the heat!
 
Newbomb Turk said:
As AndyF said above, pump gas looks sooty like that.
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There is no difference between street fuel and race fuels when it comes to colouring plugs. It takes more heat to gas the street fuel that's why you get white plugs because its LEAN at time off ignition.

The OP should try some Avgas and see how that performs. Or try a smaller carb to increase the vacuum to vaporize more fuel.
 
Hysteric said:
There is no difference between street fuel and race fuels when it comes to colouring plugs. It takes more heat to gas the street fuel that's why you get white plugs because its LEAN at time off ignition.

The OP should try some Avgas and see how that performs. Or try a smaller carb to increase the vacuum to vaporize more fuel.
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lol dude, you are dead wrong.
 
the coloring will be different pump gas to race gas. The VP blue I run is…..well…. blue. The dye and the lead effect what the plugs look like. C12 is green. The cut plug I posted is more than likely VP blue.
 
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Hysteric said:
They all colour plugs.......
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Still wrong. Doubling down won’t make you correct.

If the OP puts color on the plugs it WILL lose power.

Edit: I just got off the phone with VP and the dude said most VP fuel sold down under is blended down there (or close to it) using crude from different sources than we have here.

He said outside of the stupid cost to blend, package and ship fuel from here to Australia you have laws to deal with.

Again, you’ve been told you are wrong but you double down on it.

Anyone can pick up the phone and call VP. Then they’ll know you are talking out of your hat. Again and still.
 
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Didn't want anyone thinking I wasn't following up. Got some travel in front of me for the next few weeks. Starts with about a 45 mile round trip in the avatar on the streets tomorrow so I'll pull/save a plug or 2 before I do that so I can cut them open. Stay tuned. And thx!!
 
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Well I just had to go pull the rest of the plugs and then cut one open. All 8 of the ground straps look the same - they are clean from the tip down to around 0.090-0.100 from the thread body (pics don't show it too well hence my measurements).

Here's a pic of the one I cut open (happens to be #6). Remember this is on pump 93 fuel.
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It looks like the dark ring is a tad over 1/8" up from the insulator step. Also know this plug was not pulled at the end of the track but was essentially pulled after driving back to the pits and sticking the car in the trailer.

It should also be mentioned that all the plugs have roughly the bottom 2-3 threads showing darker/sooty.

So there we have it. Perhaps a tad in the rich side? Temps did climb throughout the day from 63 upon arrival to 87 when the last pass was made. And I didn't change any jets as I didn't need another variable! (The car ran 11.140 off the trailer at 63F (455 DA) and 11.162 on the last pass at 87F (1980 DA).
 
Demonx2 said:
I should have listed the heads right up front - my bad. They are simple Eddie RPM with somewhat mild bowl porting. So I believe these to be the limiting factor for my combo.
It's not that I'm not happy with it. But like everyone, I want to get all there is out of what I've got!
Click to expand...

If I had to guess, the limiting factor is the heads. Even fully ported, they are small on a 4 inch motor. I have had many a 4 inch motor wheeze the last couple hundred feet with such heads.
To me, the cam is a good 10 degrees too small as well. My cam in my stroker is 260@50, and I know it’s a big limiting factor.
I swapped it out of my previous stock stroke 360 and used it in this new motor merely because I had it..lol
It ran 11.22 at almost 119 at 3360 at 10 to 1 in that 360. Maybe a touch big, but definately a good bit small now. Excellerator, 950, 1 5/8 Doug’s headers.
 
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