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.

 

what is your steam line/hose setup ??? I have all four corners hooked up so that no air can be trapped in the system !!

 

LS6 has the rear 2 ports blocked off. Post failure I've come across some stuff on this.. I already have a 4 corner to put on the engine. I'm kinda doubting it's related or will help much, but it certainly can't hurt.

 

I feel as though that can trap air in the rear corners or not have enough circulation. Just my common sense opinion !! I never have any trouble filling my coolant system with a four corner setup !!

 

There doesn't seem to be a smoking gun.... so just any little thing I can do, I might as well do it/try it out.

This post is one of the more interesting ones I came across in my search on the topic:

http://ls1tech.com/forums/forced-ind...ml#post6180624

 

just seems like common sense to me !!

 

Do you know what your dyno AFR was set to? I know my tuner keeps it quite rich even if it means losing a few hp.

 

12.5 or slightly richer. I have a wide band installed in my X pipe.

 

So what pistons/rods did you go with? Anything else upgraded?

I suffered the #7 cylinder failure at the track in Nov, but haven't pulled anything apart yet. I've done a compression test and that cylinder is very low. I picked up a leak down tester last week so I'll do that for kicks and giggles. I've been reading and learning, trying to decide what I should upgrade when I put it back together. Going to be on a limited budget though.

 

5.3 alum block punched out to 5.7 (what most builders do these days). Scat I beam rods w/ ARP rod bolts. Mahle 4032 stock compression/bore pistons. Builder recommended teflon coated bearings and one of the higher flow DOD oil pumps (which i know is a controversial topic, but I went with their recommendations). Nothing crazy... I wanted to address weak area #1 pistons and I've read the rod bolts are another weak area. The scat rods were not much more vs stock replacements and included ARP bolts, seemed like a no brainer to me.

I already had AI ported 226cc heads (glad those survived) and mild 226/230 cam. Reused all top end stuff.

Let me know if you have any questions! I dug deep into about everything when I was doing my research.

 

Pounders posts are right on..if you search many post in here talking about opening the rear steam vents cause of exactly what happened here.

 

After reading your post, you misinterpreted my reply, I said to have steam lines (hoses) to all four corners. Now I have just looked it up and depending on HP you don't want to do it that way ?? The article said you don't want flow, but pressure to cool the rear cylinders. Maybe someone else will add their two cents ??

 

After reading and knowing how hard it is to refill the coolant system, when I installed my LS 6 intake common sense told me that the way the system is stock I could see how easy it would be to trap air in the rear of the engine. My feeling was if there was air trapped in the rear of the engine, it would cause problems !! I have a 180 stat and a tune to turn the fans on earlier and my car runs at 192 most of the time.

 

Yeah, I reread my post and I can see where I confused anyone who read it (including myself).

Back when I added all my boltons I also opened up the rear steam ports (because of the cylinder 7 issues).

I removed the caps and added the same steam crossover pipe as on the front. It fit perfectly (I was afraid the stem would be in the firewall). I ran a hose around with the heater hoses and tee'd it into the front steam line going to the radiator. Burping the coolant system is easier and after the car cranks and runs for five minutes you can feel the heat in the hose from the coolant.

Most of the issues you see like the OP's is from an air pocket around the back cylinders. People forget to burp the coolant system to get rid of the air pocket(s), steam builds up (not allowing the coolant to move around the cylinder) and eventually cracks the cylinder wall from pressure.

I don't believe detonation had anything to do with it as the top of the piston is too clean. Of course that's my opinion and you know what that means.

Sucks OP to be a statistic of cylinder 7. Glad you got it back on the road.

 

Not sure if this is helpful but I use an airlift pump religiously when refilling the system.....especially tricky ones that that have inverted air pockets.

By all means, follow the published procedures, but I've found the airlift gets the pockets every time.

http://www.tooltopia.com/uview-550000.aspx

 

I want to know were is the missing piece?

 

It appears to have broken off in small pieces and made it's way out the exhaust. I didn't really find anything significant in the intake manifold. minor nicks on the piston top and cylinder head, but thankfully it didn't take out the heads or valve or anything.

 

Any benefits to punching out the 5.3L aluminum block vs finding an LS6 block?

 

I have an 02 ZO6 that I did a heads, cam, ported fast 90 package on. One of my worries was just what the OP experienced.

SO,,, I did the rear steam cross over conversion. Here are some pictures of it pre installed and installed. Worked out nice.

OEM caps:




OEM 2001+ Front steam pipe crossover flipped around on rear vents:

 

Quick question guys. I'm an old fart with lots of small block Chevy eexperience but am new to LS engines. I've seen this #7 cylinder failure many times online. I'm about to super charge my C5 LS1 with all standard bolt-on stuff.

These post leave me a little confused. Is it generally accepted that the rear coolant lines mod is desirable? In all cases? Or not?

And, can this mod be done in car with intake and heads removed?

Thanks