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Location: Sweden
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The icepick
Hello!
A gentleman on another forum uploaded picture of his JE piston that has been living in 924 Turbo with slightly bad fuel injector. I tought it would be a nice picture to share, as many people ask how knock influence pistons. This is a JE piston and it survived the treatment quite well (no edge erosion, yet) but the hacks are interesting to see. It's like someone took a icepick and wen't loose on it... 
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11-25-2007, 04:47 AM
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Forced Induction Junkie
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Thanks Goran.
Looks like the piston is suffering from frost bite!  Interesting detonation effect. Did the spark plug electrode(s) suffer damage? It almost looks like there was a small object floating in the combustion chamber.
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Dave '85 930 Factory Special Wishes Flachbau Werk I Zuffenhausen 3.3l/330BHP Engine with Sonderwunsch Cams, FabSpeed Headers, Kokeln IC, Twin Plugged Electromotive Crankfire, Tial Wastegate(0.8 Bar), K27 Hybrid Turbo, Ruf Twin-tip Muffler, Fikse FM-5's 8&10x17, 8:41 R&P |
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11-25-2007, 05:22 AM
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Wo ist die Rennstrecke?
Join Date: Mar 2004
Location: St Johns, FL
Posts: 1,210
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Good pic - thanks.
This was caused by a bad (lean?) injector? The rest of the engine specs would be interesting, if you have them (timing, CR, etc). |
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11-25-2007, 06:34 AM
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Alrighty now.. since we're on the topic, guess I'll share some pics from a spare motor I purchased off a frustrated individual a couple years back.
Seems this guy thought he was up shifting and insted was down shifting at speed. I bought the grenaded motor for what was salvageable from it, and was able to scrounge some other pieces to use for my EFI build down the road. Anyway these are photos of up shifting gone bad!     
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RGruppe #180 So many cars.. so little time!! |
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11-25-2007, 08:04 AM
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Quote:
As far as I know, engine is stock 931 engine borde to 87mm and fitted with custom JE pistons. CR is unknown to me but only one cylinder suffered.
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11-25-2007, 11:58 PM
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Location: Ballston Spa, NY
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I can say I have NEVER seen that happen from detonation or even pre-ignition. That to me looks like foreign object impact.....scratches in the dome of a piston from detonation????
That piston looks exactly like the JE pistons that were in a mazda miata motor that ingested a speed loaders worth of toy bb gun ammo apon startup (speedloader fell into aircleaner and was not noticed). Search the mazda forums and you'll find that old post...... That to me looks like the piston dome was "shot peened" with nails............
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Adam Hennessy |
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11-26-2007, 10:55 AM
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+ lurking - contributing
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I tend to side with Adam, though further investigation is needed. The depth and total coverage of the marks look like something rattling around in the chamber. Not much carbon crust either. I wonder how the valves and cylinder dome looked?
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87 930 96 BMW M3 Coupe 89 951 08 Astra H Peugeot moped |
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11-26-2007, 11:16 AM
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Quote:
Exactly. The bad injector causing the lean condition may have lead to part of the piston breaking off and causing that damage, but no way did the actual detonation shock wave do that. Preignition results in holes melted into the dome and ringland transitions. Detonation results in chunks/cracks/particles that can do the damaged pictured above....either that or some part of a(burnt) valve or plug electrode/ceramic, or foreign object ingestion.
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Adam Hennessy |
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11-26-2007, 11:26 AM
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Me like track days
Join Date: Sep 2003
Location: Kirkland, WA
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Looks to me like a bit of ring or valve -
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- Craig 3.4L, SC heads, 964 cams, B&B headers, K27 HF ZC turbo, Ruf IC. WUR & RPM switch, IA fuel head, Zork, G50/50 5 speed. 438 RWHP / 413 RWTQ - "930 is the wild slut you sleep with who tries to kill you every time you "get it on" - Quote by Gabe Movie: 930 on the dyno |
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11-27-2007, 01:23 PM
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beepbeep
I have seen that type damage before in both Porsches and other makes. The impingement on the top of the piston is not caused by detonation....it might have been precipitated by detonation....but that damage is caused by something that came loose, I would guess a piece of spark plug porcelain that just bounced of f the piston and the head until it finally broke appart. Or, something came through the intake manifold and got past the intake valve.....is the head off the engine? What does it look like? If it looks the same, I rest my case.
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Al Morales 77 911 S (930 steel conversion) 88 BMW M3 79 Honda CBX |
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11-28-2007, 12:11 PM
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Just asked the owner what happened. He said that the piston knocked horribly and that damage was probably made by piece of piston itself that dislodged and bounced around in combustion chamber. He found molten aluminium in the headers and turbo as well...
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11-28-2007, 12:18 PM
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Wo ist die Rennstrecke?
Join Date: Mar 2004
Location: St Johns, FL
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Quote:
Interesting. |
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11-28-2007, 04:42 PM
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1985 Porsche 930 Fac. Slantnose 3.3l
