[Z06] Another exploding LS7
04-27-2016, 04:09 PM
#82
Premium Supporting Vendor
I am waiting to see if any of these builds from Katech or Lingenfelter etc. come back showing signs of wear, now that some of them must be getting some mileage on them. I have a hard time believing with Katechs experience with these motors that they can't get this thing right. This just can't be that complex a problem to solve, and I can't believe it has gone on this long with no answers yet.
No answers yet? You mean from GM? They're never going to do anything beyond warranty broken engines that are in warranty and unmodified. If you mean answers on how to fix it we've had it for years.
04-27-2016, 04:10 PM
#83
Premium Supporting Vendor
Well, add me to the list of the LS7 owners who blew up a 427
I had checked the posts about the valve guide issue and had surmised (incorrectly) a couple years ago when I bought my 07 with 9k miles on it. It currently has 23k miles and I almost completed my 16 track day at Watkins Glen since 2012 when I bought the car. I trailered the car there for the first time - fortunately - and no one was injured from the resulting oil slick on the track between turns 2 and 3 in the Esses. I was running about 4k-4500 RPM, I'm guessing and I lost power, heard a loud pop and saw some debris and white smoke coming out of both sides of the hood. I would say we could call this a catastrophic failure as the preliminary investigation has revealed the front left corner of the block is gone. Here's a view from below. The first suspect is the valve guides, but I'll be looking deeper this weekend. I was 2-1/2 laps into the last session of the 2 day event and feel bad for the rest of the drivers in the group who lost the last 15-20 mins of the session and the M3 driver caught in the slick who crunched the wall with his rear bumper. Of course up until then, I was having a great time and the car was flawless. I had no indications prior. I'll be digging up the old posts on the valve guide issues and planning my next steps...anyone who tracks these beasts needs to check those valve guides! 
I had checked the posts about the valve guide issue and had surmised (incorrectly) a couple years ago when I bought my 07 with 9k miles on it. It currently has 23k miles and I almost completed my 16 track day at Watkins Glen since 2012 when I bought the car. I trailered the car there for the first time - fortunately - and no one was injured from the resulting oil slick on the track between turns 2 and 3 in the Esses. I was running about 4k-4500 RPM, I'm guessing and I lost power, heard a loud pop and saw some debris and white smoke coming out of both sides of the hood. I would say we could call this a catastrophic failure as the preliminary investigation has revealed the front left corner of the block is gone. Here's a view from below. The first suspect is the valve guides, but I'll be looking deeper this weekend. I was 2-1/2 laps into the last session of the 2 day event and feel bad for the rest of the drivers in the group who lost the last 15-20 mins of the session and the M3 driver caught in the slick who crunched the wall with his rear bumper. Of course up until then, I was having a great time and the car was flawless. I had no indications prior. I'll be digging up the old posts on the valve guide issues and planning my next steps...anyone who tracks these beasts needs to check those valve guides! How many hours are you on track at your average track day? Did it have any hours on it before you bought it?
04-27-2016, 07:34 PM
#84
Advanced
What the H! I'd still like to know what the closed loop issue is...Anyone
Just received an email from Kohle over at AHP letting me know my Zo6 is ready to go.
Now if I can just figure out how to get back up there. Rick
Just received an email from Kohle over at AHP letting me know my Zo6 is ready to go.
Now if I can just figure out how to get back up there. Rick
04-29-2016, 12:46 PM
#85
Melting Slicks
They have come back. Ask Painrace on this forum. He had his engine back for rebuild and the guides looked great after our fix.
No answers yet? You mean from GM? They're never going to do anything beyond warranty broken engines that are in warranty and unmodified. If you mean answers on how to fix it we've had it for years.
No answers yet? You mean from GM? They're never going to do anything beyond warranty broken engines that are in warranty and unmodified. If you mean answers on how to fix it we've had it for years.
I could ask the same question of another customer of yours named Jim who has had his engine/heads in your shop for complete rework twice. But, IIRC when I did ask you about that Jim's heads, your response was that prior to the first rework the stock heads were simple sent out for rebuild/fix as part of your standard operating procedures without determining if indeed there was a problem with the guides to begin with.
Cheers, Paul.
04-29-2016, 03:35 PM
#86
Le Mans Master
SOME have speculated that additional / excessive heat is generated while operating in CL mode, as that is a bit learner AFR than say under WOT conditions (which with the factory tune drops into the 11.8:1 range). The theory is this additional heat from the leaner mixture might contribute to coking (cooking) the oil on the exhaust valves, causing issues with lubricity, build-up on the valve stem and potentially resulting in the valve hanging in the guide, causing piston to valve contact, etc.
The issue with this theory is when the engine is running in CL, it is (for the most part) running at low load and throttle positions. In general, high-load / large throttle positions equate to moderate to high cylinder combustion temps and switching to Open Loop with lower AFR's, low-load / small throttle positions equate to low cylinder combustion temps.
In my opinion, and slowly being proven out by good long-term valve guide clearance reports from re-worked heads, this theory doesn't hold a lot of water as a significant contributor to the LS7 valve guide issue.
Last edited by Dan_the_C5_Man; 04-29-2016 at 03:41 PM.
04-29-2016, 03:38 PM
#87
Team Owner
Member Since: Feb 2005
Location: FL
Posts: 40,971
Received 320 Likes
on
152 Posts
CI-7-8-9-10 Veteran
Cruise-In IX AutoX Winner
St. Jude Donor '05-'06-'07-'08-'09-'10-'11,'19,'22
St. Jude/CI Name Tag Designer
I feel your pain brother. Mine went with 16,750 miles, albeit EXTREMELY hard miles. Been full-time autocross car from week 1 after the museum delivery. Mine's a 2008 delivered in October 2007. The only rub here is I had valvetrain issues and metal in the pan, and shipped heads off to be rebuilt with all the best stuff. Still dropped a valve and blew up cylinder 1.
Hoping to fire up the new engine this weekend. Texas Speed & Performance built LS7 - Heads/Cam/Fast LSXR 102 Intake and 102 throttle body/Tune/Long tube catless headers. Car will be down to 2,900 pounds shortly too.
Hoping for about 580 at the wheels. 
Mine went with 16,750 miles, albeit EXTREMELY hard miles. Been full-time autocross car from week 1 after the museum delivery. Mine's a 2008 delivered in October 2007. The only rub here is I had valvetrain issues and metal in the pan, and shipped heads off to be rebuilt with all the best stuff. Still dropped a valve and blew up cylinder 1. Hoping to fire up the new engine this weekend. Texas Speed & Performance built LS7 - Heads/Cam/Fast LSXR 102 Intake and 102 throttle body/Tune/Long tube catless headers. Car will be down to 2,900 pounds shortly too.
Hoping for about 580 at the wheels.
Last edited by Datawiz; 04-29-2016 at 03:49 PM.
04-29-2016, 06:13 PM
#88
Burning Brakes
@Datawiz
Nice pics. 1 7/8 ceramic coated headers I assume?
You had your heads reworked and you still dropped a valve and blew up cylinder 1. How do you think that happen?
Nice pics. 1 7/8 ceramic coated headers I assume?
You had your heads reworked and you still dropped a valve and blew up cylinder 1. How do you think that happen?
Last edited by starchedup; 04-29-2016 at 06:14 PM.
