What caused this?

[Mike S]

I've got an 86 SVO with a Rapido aluminum head, stage 3 ported by Boport with his 2.1 stick. It also has one of his gutted ported upper and lower intakes. After a recent upgrade to the Siemens 60 lb/min injector to use with my pimp, I ran the auto tune to get the VE table back in shape. I thought I had done enough runs to get it close and wanted to do some 15 psi runs, so to be on the safe side, I raised all the VE values in the boost range by 10 before taking a run. Apparently, 10 was not enough and it started sputtering and running like I had blown the head gasket between 2 and 3, so I limped it home, ~10 miles.

Unfortunately, it was not a head gasket. I started to pull the plugs to conduct a compression test and found that detonation blew off the electrode on #2 cylinder E3 spark plug and insulator.
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So I got a bore scope to inspect the damage and it was enough that the engine had to come apart to get all the shrapnel out and inspect the cylinder wall. Here are photos of what i found:

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#2 Piston

Strangely, I had some damage on cylinder #1 as well. I'm not sure how this happened:

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#1 Piston

Notice the difference in the amount of carbon build up? You can see it plainly in this photo comparing all four pots. The photos are before any cleaning.

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So my question is, what could cause the one clean piston top? Too lean? A bad new injector?, More air flow to #2 runner due to the gutted port job on the intake? The excess gas washed it clean on my trip home beacuse the plug wasn't firing properly? What do you think?

[MikeFleming]

The excess gas washed it clean on my trip home because the plug wasn't firing properly? This.

IMHO - stop using those multi-ground electrode plugs. I've never seen anything to be gained from them.

In boosted applications that have a tendency to detonate I much prefer the [single] ground electrodes that completely cover the end of the center electrode - so when the center ceramic does fracture, it will fall down and close of the gap without falling into the cylinder. and if it breaks apart, only small pieces get embedded into the piston tops/lower cylinder head area (mostly on aluminum heads).

The dents on the other piston are curious. What intake are you running? Could that be from a previous failure that went undetected? Although they do look fresh.

[Raven855]

So my question is, what could cause the one clean piston top? Too lean? A bad new injector?, More air flow to #2 runner due to the gutted port job on the intake? The excess gas washed it clean on my trip home beacuse the plug wasn't firing properly? What do you think?

Most likely it was detonation that cleaned the top. Mike brings up some good points. What caused the pitting on the other Pistons? And get rid of those fancy plugs. A nice plug to use is the platinum NGKs. Along with your A/F setting I would check the plug heat range, it looks off. I would check the timing also, it doesn't look right.

[Mike S]

I would check the timing also, it doesn't look right.

What leads you to this conclusion? Base timing is 10* BTDC and the rest is from the base PIMP tune.

Do you recommend colder or hotter plugs?

[Mike S]

This.

IMHO - stop using those multi-ground electrode plugs. I've never seen anything to be gained from them.

In boosted applications that have a tendency to detonate I much prefer the [single] ground electrodes that completely cover the end of the center electrode - so when the center ceramic does fracture, it will fall down and close of the gap without falling into the cylinder. and if it breaks apart, only small pieces get embedded into the piston tops/lower cylinder head area (mostly on aluminum heads).

The dents on the other piston are curious. What intake are you running? Could that be from a previous failure that went undetected? Although they do look fresh.

This is the first problem I have had with the E3 plugs and it wasn't their fault. These have two seasons of track time and tuning on them without issue. The intake as stated is a gutted and ported Boport intake. I'm guessing the insulator parts got transported to cylinder 1 during decel.

[MikeFleming]

This is the first problem I have had with the E3 plugs and it wasn't their fault.

Doesn't matter whose fault it was - the result is that the whole broken insulator fell into the cylinder in one piece, to get pulverized by repeated impacts between the piston and head. Single-ground-electrode plugs don't do this.

Other than the marketing claims from E3, I've never seen anything to be gained from their "technology" especially without a thin wire, precious metal center electrode. Similar to gap-less piston rings. While gap-less rings do give great leakdown numbers, initially, none of them have made more power on a dyno nor gone down the dragstrip any quicker.



The intake as stated is a gutted and ported Boport intake. I'm guessing the insulator parts got transported to cylinder 1 during decel. Difficult to say. That's still 8+ inches to travel upstream. Something large got into the other cylinder though and broke into smaller pieces after some impact(s). I would've expected to see more impact damage n #2 though.

Luck of the Irish, I suppose.

[brsvo]

When I have blown head gaskets coolant has caused the piston to be cleaned or so I assumed.

[Mike S]

I guess the lack of color on cylinder #2 hides the amount of damage. There is actually more damage on #2 than #1 when you feel it with your hand and look close.

Thanks for the feedback.

[MikeFleming]

I guess the lack of color on cylinder #2 hides the amount of damage. There is actually more damage on #2 than #1 when you feel it with your hand and look close.. If your camera has a macro/close-up setting, that will help show the details. Add some light to help it focus.

[Raven855]

A generalization of plug reading is done by looking at the porcelain, the ground strap and the first few threads of the plug. The E3 plugs can mislead you at times and so you need to take some extra care in reading them. Everything I have read about the E3s agrees with Mike. Save your money.

You asked about the timing. I mention the timing based on what I am seeing on the ground strap. A better picture would help as would a picture of the porcelain base and knowing more about the engine and fuel but to avoid any misreading a tradional plug with fewer miles would be more helpful. I don't know what the heatrange is on your E3s so it is difficult to recommend a heat range. I included a picture from a recent discussion on plugs. It shows the heat line on the plug threads. Compare it to yours. Can you see the line. Look at the ground strap, see the coloring. From a write up on plug reading "Ignition timing is directly responsible for the heat in the combustion chamber and therefore the color of the plug’s ground strap and the color of the first few threads on the outside of the plug. The ignition timing can be checked by looking at the color of the plug’s ground strap and the position of the "blue line" on the strap. The blue line really indicates the point at which the strap has reached annealing temperature of the metal. To help to understand this think of a bar of steel (ground strap) on a table that is being super heated with a acetylene torch at one of the tip ends. As the end heats up and the heat starts moving down the bar you will see a blue line across the bar at some point down the bar away from tip with the torch. This blue line reflects the temperature that is the annealing point of the metal. As the temperature increases the blue line moves further down the bar away from the torch. Similarly, the blue line moves down the spark plug ground strap as you put more heat in the engine." That's from here and for more reading http://www.dragstuff.com/techarticles/reading-spark-plugs.html. It's a good primer and start.
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[TurboRay]

The dents on the other piston are curious.

What caused the pitting on the other Pistons?
"Trash Swapping" between cyls is very common on blown-up engines, even with extremely-convoluted intake manifolds/runners. I've seen it many times, due to the almost-inconceivable pulsing forces therein. If you should ever overhaul a motor with divots &/or trash on or embedded in the piston tops......ABSOLUTELY clean out the intake plenum/runners with solvent and compressed air prior to reassembly. Don't ask how I learned that lesson! :(

QUESTION: Would detonation/preignition have occurred with no spark?

[Under Pressure]

QUESTION: Would detonation/preignition have occurred with no spark? Yes I had the same pitting marks on my #1 piston when #1 had a meltdown.