Does this look like detonation?

[JMD]

Hi all, the engine in question is a 454 with a mild cam, aluminum heads, and a 9:1 compression ratio on 91 octane gas. It’s controlled by Holley’s sniper EFI.
So I’ve been messing around with my new Holley Hyperspark electronic ignition and it’s definitely made the truck more responsive. I’ve been slowly bumping up the WOT timing, but I’m worried I might have gone too far advance. I currently have the controller set at 40* advanced. I know, that’s way too much. However, I’m pretty sure the cheap timing pointer and harmonic balancer combo I have does not give an accurate TDC reading whatsoever. This means that my 40* of advance could be way less.
I haven’t heard any detonation, but that doesn’t mean it’s not there. I pulled a few spark plugs and for the most part they looked great (a nice brown color) except for #6 which is pictured below. Is this what detonation looks like or do I have a different problem?

[71cadc10]

generally detonation would show itself as 'black pepper' looking specs down inside on the white porcelain.
you would want a magnifying glass and good light to look down in there better, or sacrifice the plug by cutting away the threaded steel to expose the porcelain fully.

[toolboxchev]

Not to me, I have yet to see a diagram showing exactly what detonation looks like.

Its burning something in there. Maybe running lean or rich on that cylinder. AF ratios can be very different from a standard intake manifold.

White ash is a hot situation if I remember correctly. Could be leaky valve, excessive piston ring blow by, If you can put a sensor on that cylinder it would tell you more.

[garyd1961]

The first thing I would do is double check my timing mark.

[maynardogle]

An insulator that white seem awful lean. Shouldn’t there be a little mocha tinge?

[Portland68]

It’s hard to tell from the picture but is that plug gapped correctly? It looks small from this angle

[72LB]

Looks like crappy gas and a bit lean.

[HO455]

As 71cadC10 said you need to cut the plug or get a Ophthalmoscope or equivalent magnifier to see what is in at the base of the porcelain.
Remember you have to pull the plug immediately after your WOT run. Driving the vehicle back to the pits or idling around the neighborhood causes the tell tales you are looking for to be covered or removed by running the engine at other than WOT. Go to the link and click on Nerdletter #3 for some enlightening on plug reading.
To start I highly recommend you get the balancer pointer issue solved. Then make sure your valve adjustment is correct. Then start again with your timing.
As a second recommendation I suggest getting an wide band O2 guage and you will never need to try and interpret spark plugs.


https://www.cherylyoungonline.com/Pat Usher/index.html
Then read Nerdletter #3.

[JMD]

Thanks for the suggestions guys, I’ll have some time this weekend to mess with it and I’ll report back with what I find. I also bought a piston stop tool so I should be able to nail down true TDC.
I pullEd the #4 plug spark plug and it looked perfect. Since the Holley sniper is a throttle body setup and all the cylinders are getting the same fuel mixture, wouldn’t that rule out a lean condition?
The sniper also comes with a handheld lcd screen that gives me more information than I know what to do with, including a/f ratio. When cruising it’s right around 13.9, and it drops to 12.5ish with WOT. I did have an issue a couple weeks ago with the fuel pump failing, so I know it was leaning out for for a few miles before I could shut it off. However, I’ve driven over 100 trouble free miles since then, so I would think any evidence of running lean would be gone.

[JMD]

Timing mark was fairly close. True TDC was at 2-3* advance according to the marks on my balancer so the 40* of advance is really only 37ish. I cut the plug apart and everything looked fine farther down on the porcelain. Plug gap was a little smaller than all the other ones, .035” instead of .040. To me, it looks like a lean condition...I have yet to check the valve lash for that cylinder, could a leaky valve cause the cylinder to run a little lean?

[mr48chev]

My plug reading skills from the 60's and 70's got tossed out the window when this crappy gas came along and again when the extra crappy gas to make Iowa corn farmers rich came along.

In the 60's you could pull a plug, hold it up in front of the perfectly colored plug chart and be real confident that you knew what the issue was if you had one. Now all bets are off.

I've always seen signs of detonatin as erosion of the material though.