aaronc7

Just thought I would share my experience and what I've discovered so far. Doing all the reading/researching I can to help avoid this in the future.

2003 C5 Z06, LS6 with 226/230 .600/.600 cam, LT headers, standard bolt ons. ~47k miles on the car. I was on a road course when it happened, but I didn't really know it at the time. This was back in september, so it was pretty hot out, 90 or so. Coolant temp stayed below 210, oil temps around 260 max. LIttle high but nothing out of control.

Came off the track after the first session, noticed a tapping noise at idle before I shut the car off. I started it up a little later and to try and figure out what was going on. It sounded like it was coming more from the top end of the engine, not rod knock, but was still loud enough to alarm me. I also discovered that above 1500 rpm in neutral the tapping went away completely. I played it safe and had the car towed home.

At first I was thinking valvetrain, so I took valve covers off, checked out what I could, but everything looked normal. I noticed the oil color looked off though and suspected there was some water in it. Did a leakdown test and cylinder 7 showed 80% leaking or something like that.

Pulled the heads off, cylinder 7 piston top missing one corner (looks just like every other pic I've seen on here) and starting to crack in a different side. Head gasket looked fine (how was water and oil mixing?). Discovered a crack in the liner....which also seems fairly typical for this failure. The heads/valves were fine thankfully. Some scratch marks from the piston material exiting presumably, but very minor.

I was not datalogging at the time on the track, but I did not hear or feel any knock and historically with this tune (I had several tracks days on exact same setup) I had no knock. Didn't really see any evidence of knock I don't think in that cylinder either, just looked nice and steam cleaned.

Here's some pics of the damage. I also noticed that on cylinder 7, the piston/rod wrist pin connection is very stiff. You can move the piston on the rod, but it takes quite a bit of effort. All bearings looked fine, bummer the block is basically toast from a small little crack.

Car is back up and running now with a forged rod/pistons LS1/5.7. So far my plan includes having a more conservative tune for the track... Looking for any other ways to increase cooling/coolant flow to the rear cylinders.

slogo

Just curious, do the rear steam ports on the heads flow or are they blocked off?

aaronc7

They were blocked off. From my understanding the LS6 and the LS1 when it got the LS6 intake manifold they switched over to the fronts only. I actually already bought a 4 corner and planning to run that for good measure.

slogo

Yeah, I don't have personal knowledge if it is related or not, was just curious.
Personally I use them because they are there, and I think they are a good idea.
Good luck on the next one.

ddnspider

iTrader: (26)

I've read enough on here and elsewhere that I will ALWAYS use the ls1 crossover and not the ls6. Even with an ls6 intake I grind down the ribs on the bottom of the intake to make it fit. I remember reading and article where they flipped the intake around and 7 and 8 still were the leanest and prone to detonation so it's not the intake manifold design.

aaronc7

https://ls1tech.com/forums/forced-in...ml#post6180624

Is a pretty interesting post on the topic.

RockinWs6

I lost number 7 same thing WITH 4 corners cooling.

99 Black Bird T/A

iTrader: (4)

Pantera EFI makes some interesting comments in this thread about #7 failures.
Its post #8 and focused on spark advance.

https://ls1tech.com/forums/generatio...l#post19496576

pantera_efi

iTrader: (1)

Hi Guys, those "high paid" MODDERS should move this thread.

I too am concerned.

ONCE, I stated to the FORD 4.6 Engineer, " The cam tension guide, with piston, was INCORRECTLY placed, on the THRUST side!"

HIS answer, "impossible".

Later that day I got my answer.

Lance