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Pulled the head off...
https://slantsix.org/forum/viewtopic.php?t=37602		 Page 1 of 1
Author:  Shaker223 [ Thu Oct 22, 2009 8:48 am ]
Post subject:  Pulled the head off...
As you may or may not have know my slant finally succumbed to all the pounding!! Below are some pics that I took of the head gasket and piston/block. It got me home fine but had some really mean internal blow-by.

Until I get the piston out of the block I may not know what caused the problem. I don't know if it was detonation or the piston cracked with 29psi of boost. I can get a dental pick in there but can't move the ring. I can see around 75% of the bore and the ring is still intact with no cracks which might be an indication of no detonation. The other cylinders are similar in that I can see the top ring and they are not broken.

Initially, I don't think it was detonation because I had a pretty healthy mix of 110 octane in the tank (in addition to the 9gph meth jet), timing was at 22* and the AFR on the last pass was around 11.9:1. We will see.

The ARP 7/16 head studs are not strong enough with 4 bolts per cylinder. As you can see, there are witness marks on the copper headgasket of it lifting.

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Author:  slantzilla [ Thu Oct 22, 2009 2:34 pm ]
Post subject: 
I can tell you from experience that it looks like that piston and gasket got plenty warm. :shock:
Author:  Joshie225 [ Thu Oct 22, 2009 3:01 pm ]
Post subject: 
I'm reminded of a song. Under Pressure

I agree, that piston and gasket got hot. I'd bet you collapsed the top ring land and pinched the top ring. 11.9:1 may have been the overall A/F ratio, but I'm sure it varied from cylinder to cylinder. With that much boost and heat (got intake temp data logging?) you were really pushing your luck. You may not have heard any rattling, but it's still possible to get preignition and run the combustion chamber temps way up. Without knowing the intake temps, or assuming that they were not way too high, I think you've hit the pressure limit and need to spin the engine faster to make more power.
Author:  Shaker223 [ Thu Oct 22, 2009 3:10 pm ]
Post subject: 
Other than the overall AFR, I don't have the individual cyl AFR. I certainly didn't hear anything rattle which is normally the case. Outside air temps were 46*f. In the past, when I measured air temp after the meth jet it has been 10*f less than ambient.

Some of the previous runs to this one were definately lean (12.5:1) so I jetted the secondaries up 4 sizes to 89's. The damage may have been done prior to this run and this final run is where it happened to let go.

Good news is the little missing piece did not damage the turbo.
Author:  Shaker223 [ Thu Oct 22, 2009 6:59 pm ]
Post subject: 
Quote:
I can tell you from experience that it looks like that piston and gasket got plenty warm. :shock:
Not so sure on the gasket. It has been pushing out water since I put the copper gasket and studs on. No runs leaks or drips were ever visible but after every track session or hard driving I had to top off the rad.
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