Re: Auto engin question.
 

That kind of damage sounds like detonation. However, by your description of the color of the top of the pistons, it doesnt seem likely. How many miles on the engine? Is there a ridge in the bore above the pistons? Maybe the pistons hit the ridge? I would be curious to see what the other 3 pistons look like. I am baffled at how all 3 pistons can have the exact same damage. That tells me that the problem is not specific to one cylinder but rather at least that half or possibly the enitre engine. If you want, I have a few hooks at GM. I can try to reach out and ask if they have seen this before. As I said, I have never worked on a supercharged version of this engine.
I just had a thought... I have changed numerous cat converters on these engines. They go bad and clog up all the time. So badly, that they can blow a hole in the plastic plenum directly above the egr port, just behind the throttle body. I wonder if it is possible that can cause enough backpressure to heat up the intake charge and snap off the top of the pistons?? Especially with a supercharger.

Re: Auto engin question.
 

Do any of the intake valves have damaged seats or bent valves? If something "came into" the combustion chamber, it would likely leave chicken tracks in the intake seat. I'm not sure what the blower intake on that motor looks like, but if the pistons were on the rear side of the motor, it could be a piece of debris that rattled back and forth between those jugs. Intake manifold design would either allow this (open plenum) or not (long runners).

How does the piston wash on the slugs in that bank compare to the ones on the other side? Do they all look to be running the same?

Exhaust restriction on one bank is possible, but I would think that a computer code of an O2 out of range error would be stored.

Re: Auto engin question.
 

Theres no ridge, just normal surface scraches "very fine the engin looks brand new other wise.it has 60k miles ,I bought it new @ 15k i installed smaller sc pully and K&N air filter and houseing, when it happened she had drove it the day before and said it ran fine,next day she starts it up and its missing and tapping,she didnt even drive it.

It must be detonation I just don't see how with knock senser and rev limiter, engin light did not even come on.

Re: Auto engin question.
 

Sorry I've been typeing with 1 finger for the last ten min. plus I'am on dial up,I did'nt read your post til after my post.

Re: Auto engin question.
 

All the pistons are solid black, "in color only" no carbon build up, I pulled 1 intake valve and no sighn of nicks or tracks, the intake runners look like brand new "no carbon" the ex are black and sootie,I see 1 shinny nick in blower vaines, but it looks and feels smooth turnning, I looked at it close for any thing that could have broken off.

Re: Auto engin question.
 

I havn't pulled the other side off, the engins in there sideways.

Re: Auto engin question.
 

Yeah, that back cylinder head is not easy to get off. I wouldnt bother. You have to pull the engine out to make these repairs.

Re: Auto engin question.
 

I bet it was detonation,the color of the piston does not rule it out.you can still detonate on a rich mixture

Re: Auto engin question.
 

Maybe the timing belt was off? If the 3.8 is a so called "interference" engine, a bad or mistimed belt could be the culprit.

Re: Auto engin question.
 

In my shop,I have seen a couple 3.8's hang the intake valves during a severe redline episode( kids drivings mom or dad's car) :) make sure ya check the heads out.