outhouse

Darin Morgan


I received the heads in question yesterday, tore them down and measured the guides. When they where brought in years ago they where almost new. They had .0015 clearance with about .0005 taper. They now have .0016-.0018 with .0015 taper on the worst guide and the rest have about .001. Yes, they are wore but they are not totally "wear out". I will note that the end exhaust ports are always the worst because of lack of water circulation in that part of the head. #2 #8 exhaust ports always wear more than the rest.

These are stock guides and at the time of rebuild many years ago I did not replace the guides because the guide issue was not a proven fact at that that time and the guides where great. These heads came from 21st century and they did a great job on them! I just freshened them up and sent them down the road. Now days when it come to guide wear on the ls7, we know better and we understand that the exhaust guides can have accelerated wear especially in conjunction with high lift cams. I now replace ALL guides on LS7 heads. I use the CHE high Nickle bronze which is more than sufficient for street use. All bronze guides are not the same!!!!!!! There are over 70 different formulations of bronze guide material! If you buy the cheapest Chinese Bronze ****, its going to wear FASTER than a stock guide! I can buy bronze guides for 1.02 each or pay for the ones that will hold up and pay 5.50 to as much as 8.00 each. If its cheap, its cheap for a reason! When someone complains about how fast there bronze guides wore out, ask them if they even know what type or manufacture they used because if you use CHE and give them adequate oil flow, you wont see that ****. I dont see my heads coming back with guide wear using CHE guides as should be the case!

On another note:
How many of you guys take a razor and slice the seal on the exhaust guides? If you do this they will get the oil they need but WILL NOT contaminate the cylinder. It will also cut your guide wear in HALF no matter what material you use. I also take off the springs at the top of the seal because its a joke to run that tight a seal on a "High Performance" engine. The ONLY reason the factory cut the oil flow to the guide down to a minimum is to pass EPA standards. If the guide is wearing thats a LACK OF LUBRICATION! Get some oil to it and it will stop. We NEVER run seals on high end race engines. The more friction you have, the more oil you need. It could not be any more simple.

The_Raging_Bull

I wont assume the worst of Chevy's behavior. I dont want to get flamed here, but too often the the reason that there were so many long CF threads on dropped valves was everyone and their cousin had an opinion; and seldom was the discussion dispassionate. Also too many folks would post, I would argue to some extent to state an opinion - based on what they read of the issue.(Not fully data based/facts ) I understand how you feel, but too many threads get jacked by folks venting; as I said I hope we can discuss it w/o wrecking the thread.

I too understand the issue. Personally I think Chevy reacted poorly to the Z06 fiasco..but that doesn't mean that in the background there weren't changes made in the Z/28 LS7. Certainly in the 1700 to 1800 Z/28's (between the S/N produced and the captured test fleet cars) the number of issues with dropped valves has been nearly non-existent, and there are cars with 15,000 to 20,000 miles on them; which as I recall was the sweet spot for failure in some of the Z06's that dropped valves. Based on the lower frequency of dropped valves I would say that Chevy did something... Hib published his results in 2013, and a year later as Chevy released the '14 and '15 LS7's for the Z/28 fleet they had a chance to quietly address the issue .

If you haven't ever ridden in a Z/28; you should appreciate its like a (C6)Z06 Camaro..its one bad aZZ car. The C6Z06 engine, tranny and drivetrain were dropped in, along with the Brembo CF brakes; and its a complete package with an engine tune that is clearly competitive with my '09...it just weighs more. If the opportunity presents itself..be sure to take a ride in one; it is a complete analog track car...old school and nothing but fun. I get way more comments on it than any corvette I ever owned...nearly every time I'm out or at gas stations; as people say they've only seen them in a magazine.

Again, I walked into my purchase eyes wide open. I wanted a 427 in my Z06, then last year the opportunity presented itself to own a Z/28 (due to an idiot totalling my wife's 2011 2SSRS - yahhoooo!). I'm sending the Z06 to Katech this year; and I have a 7yr 70000 mile warranty on the Z/28 >> insurance taken out as a "just in case" because of the Z06 dropped valve issue. In 2022, I'll send the Z to Katech to address any issues as it reaches warranty's end.

sublime1996525

Unreal

Z06 drivetrain was not dropped into a z28. One is a transaxle design, one is not. Only thing they share is the motor, but tranny, drivetrain, rear end, etc etc are all different.

outhouse

Doesn't mean they made any changes, and since some have dropped valves it looks like they didn't do squat.


To understand the issue you have to understand the dynamic problem here.


#1 Out of spec guides
#2 Softer powdered metal guides.
#3 lack of water circulation near #2 #8 exhaust ports


There is no evidence either has changed.


There is no debate anymore on this and it is really settled based on the three facts above with #1 being primary and #2 #3 being secondary.


MOST important, worn out of spec guides does not mean failure is imminent. BUT it factually increases the odds.


Once the Z28 community starts checking for guide wear, you will see many out of spec heads. It was the same when this engine was new to the C6 platform.

Unreal

CPR just did heads/cam on a z28. Would be interesting to see if it showed wear. Was fairly low mileage though.

MTPZ06

There's a guy on here that states he's pulled a few sets of heads from the z28, and that GM used the COPO head castings. Only time I've ever heard that, but it seems plausible at least.

outhouse

COPO 7.L are 425hp. So I'm skeptical.


from what ive read and I could be wrong, its the same head.

The_Raging_Bull

On the tranny, i'm pretty sure a Tremec TR6060 in a vette= Tremec TR6060 in the Z/28..
and the Z/28 .391 rear end, is better at coming out of the hole than the Z06 0.342 I own in my '09..

outhouse

But you were wrong in stating



That was his point and he was correct in calling you out on it because the drivetrain factually was not dropped in.


Just a few words on your part no big deal

MTPZ06

If that ring and pinion could be swapped into the diff of a C6Z...they'd sell a ton of those.

MTPZ06

I think the "425hp" figure was severely under-rated. My understanding is that they make much more than that. But again, we're just talking about the head castings used from the COPO motor bolted onto the LS7 that we run...which may just mean a different CNC program for all I know?

Unreal

6060 is used in a viper, in mustangs, in all base vettes, in all base camaros. So saying it is some special pull out of z06 is a stretch. Same 6 speed manual tranny just about everyone uses.

The_Raging_Bull

Partner,
I NEVER said it was special pull...
I said both cars had the same transmission, and the same engine, and that the Z/28 was an LS7 powered, a Tremec TR-6060 driven, a six-piston front and four-piston rear cylinder Brembo CF brake stopped Chevrolet Performance badged track car.....Capiche??
Oh and I'lll go a little further, its a corvette coupe killer too. My brothers in the Tulsa Vette Sette love it when I tell them don't hesitate too long, or you'll be looking up the wrong *** end of the car as it disappears in front of you (up it's tail pipes). It'll take the C7coupe, a C6 Coupe gets destroyed...and it corners as hard , if not harder than a C6Z06 or C6ZR1. The Trofeo-R's it wears will hang it in a corner.

Folks on CF like to argue..which is why I hang around Camaro5 on their Z/28 section these days...sheesh!!

The_Raging_Bull

No ****....RPM will sell you a Z06 $3745 stage 4 differential....I too wish my Z06 had .391's....at the price of new gears....not a whole new differential .

Unreal

Its not that we like to argue, its we don't put up with misinformation. Camaro 5 people love to spread BS. Its worse than here.

The_Raging_Bull

I misspoke ..you're right really no big deal.... I do own both cars and can tell you the LS7 in my Z/28 feels stronger than the same tranny and engine setup in the Z06...I'm sure no doubt due to the differential and the added torque. The Z/28 torque is 481 ft-lb; and the exhaust goes snap crackle pop ..just a great note..better than any Gen6 Z06 of any year I've heard, and there are several in the Vette Sette. The biggest difference is the weights; where the Z/28's 3800 lb is a disadvantage.

The_Raging_Bull

I've owned a Z06 before I owned a Gen 5 Camaro, unless you count the 79 Z/28 I had that never met a vette it didn't own... with a 530hp forged engine and a 200 HP NOS shot...

It was called.."The Raging Bull". like a bull in a china closet...I had a guy blow up his vettes engine racing it in my mis-spent days in college..and the name hung-on all these years.

And.....we all love to spread BS...we wouldn't be car guys if we didn't. However don't mistake a misspoke for being a purveyor of BS and a dumbass; you might be reading too much in a quick comment on a forum.

RamAir972003

AH had never done my heads my heads were done by someone else the pm guides back in 2012 were installed on heads after 20k miles were taken apart and showed some wear on them...now I'm rebuilding my motor and doing a bronze guide che......lets see how this will last.....but yes guides are a wearable item but the question is 20k they should not have any play on them at all, ls3 heads dont do that not saying that they will never but why ls7 heads....

MTPZ06

Cam profile and 1.7 versus 1.8 rockers are probably a good part of that. Throw a hot cam and some SLP 1.85 rockers (or another) on an LS3, and I'd be interested to see the long-term effects. Certainly more variables at play, but I think those are two of the biggest contributors of wear.