[Z06] Stage II LS7 cylinder heads - A visual guide to valve guide wear and CNC upgrades
#1
Former Vendor
Thread Starter
Stage II LS7 cylinder heads - A visual guide to valve guide wear and CNC upgrades
We see a lot of LS7 cylinder heads here at Vengeance Racing and in our experience the valve guide issue is quite real and very problematic. Now, we're not here to sell anyone a set of heads (although we would be happy to ) but mainly to offer a place to ask questions and get answers.
If you are not famiiar with the LS7 valve guide issue, it is essentially a factory machining/installation error that causes excessive valve guide wear, which eventually allows a valve to drop or hang, which can be catastrophic. You can see what happens when a valve drops below...
GM attempted to ignore the situation at first, but after enough complaints they finally issued the following statement:
Hello all,
LS7 Valve guide issue summary:
• Affects a small, number of '08, 09 ’10 and ’11 Z06’s
• GM discovered the condition through our cylinder head warranty data involving a very small percentage of our vehicles.
• Through inspection of returned heads, it was determined that a machining error in the valve guide had occurred at our head supplier.
• The quality issue has been contained as of Feb 2011 with 100% inspection of all heads.
• The most common customer complaint has been excessive valve train noise.
However if the condition is not addressed, it could result in engine failure. To date, where this condition has been observed, it has occurred early in the vehicle life.
What customers need to know: They should drive and enjoy their vehicles without fear. If their car demonstrates this condition, they are likely to hear unusual valvetrain noise first....
LS7 Valve guide issue summary:
• Affects a small, number of '08, 09 ’10 and ’11 Z06’s
• GM discovered the condition through our cylinder head warranty data involving a very small percentage of our vehicles.
• Through inspection of returned heads, it was determined that a machining error in the valve guide had occurred at our head supplier.
• The quality issue has been contained as of Feb 2011 with 100% inspection of all heads.
• The most common customer complaint has been excessive valve train noise.
However if the condition is not addressed, it could result in engine failure. To date, where this condition has been observed, it has occurred early in the vehicle life.
What customers need to know: They should drive and enjoy their vehicles without fear. If their car demonstrates this condition, they are likely to hear unusual valvetrain noise first....
With a dial gauge attached directly to the cylinder head, it easy to get a quick and dirty feel regarding valve guide wear. This is our starting (zero) point...
...and here we have the valve pushed all the way up. 0.019-inches of play.
Here is a head with new bronze valve guides installed:
0.006-inches of play. Much better!
Again, that's quick and dirty. We recommend having a professional check every guide with a valve guide bore gauge (which we do) before and after the installation of new bronze valve guides. Or don't check them and just change them out, you won't regret it!
Besides correcting the valve guide issues, let's check out the rest of the VR/WCCH Stage II LS7 Cylinder Heads.
The stock combustion chamber prior to hot tanking and blast cleaning:
After hot tanking and blast cleaning:
With the valve removed, we can compare the stock valve job:
To the new VR/WCCH competition valve job:
And here are the two heads side by side, to show the before and after:
In addition to installing new valve guides, every stage II LS7 head features CNC-ported intake and exhaust runners for maximum power output.
The exhaust port features CNC-porting as well:
Each VR/WCCH Stage II LS7 cylinder head comes with a new set of one-piece stainless steel exhaust valves and tumble polished Titanium intake valves. The stainless steel valves are brand new, while the Ti valves are inspected, cleaned, and polished OE units.
Here you can see the stock valves out of a factory cylinder head:
And here are the a new set of valves. Stock diameter, although the exhaust valve has been upgraded to a one-piece stainless steel unit, and the intake valve has been polished to reduce valve guide wear.
The heads are gorgeous and safe but besides that, they flat out make power!
Exhaust port flow at at .600 is up 18.5cfm thanks to the CNC port work, from 226.3cfm to 244.8cfm. At .700-inches, the ported LS7 flows 250.6 compared to just 228.8 from the stocker.
The intake runner CNC work shows even bigger gains (using the stock valve!) with .650-inch flow up to 395.4cfm from a chocked 333.1 - That's a gain of 62.3 cfm
Of course, the real question is, what will this do on an LS7 engine? In our experience a Stage II cylinder head swap is worth 30-40rwhp in back-to-back testing.
On a well appointed C6Z with a VR camshaft plus kit, a set of quality long-tube headers, and the correct bolt-on parts, these heads are good for ~600rwhp and 520 ft-lbs of torque.
At any time, Vengeance Racing has 4 sets of Stage II LS7 cylinder heads in rotation, heading out (excuse the pun) to customers all over the world. Of course, we will be happy to answer any questions regarding this process and we welcome any discussion involved with LS7 cylinder heads in general.
#2
Burning Brakes
Great, informative post guys... That dyno graph looks familiar
She was stout at the track, ran great all weekend long - but in this GA weather and frequency, I think I see a Ron Davis in the near future. Will keep you posted!
She was stout at the track, ran great all weekend long - but in this GA weather and frequency, I think I see a Ron Davis in the near future. Will keep you posted!
#5
Safety Car
Informative write up ... thanks for sharing....
#8
Melting Slicks
#10
Former Vendor
Glad to hear your track outing went well!!! Ga heat is brutal Let me know when you are ready for that Ron Davis/Spal fan combo.
#12
Team Owner
Well this is a very nice presentation
And an open offer to discuss/answer the valve train/head issues is outsatnding.
So here is my question: Should I rip my WCCH off and yank the SS exhaust valves out of them based on your competitors recent spintron tests ????
DH
And an open offer to discuss/answer the valve train/head issues is outsatnding.
So here is my question: Should I rip my WCCH off and yank the SS exhaust valves out of them based on your competitors recent spintron tests ????
DH
#18
Burning Brakes
Member Since: Jul 2008
Location: Houston TX
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I too would like to know why not just do bronze guides, polished intakes, and new OEM exhaust valves? The valves arent defective, just the guides correct? the bad guides damage the valves, valves break. that's the prevailing theory.
#19
Ron would you agree that the stock exhaust valve isn't dealing with the heat the way it should? great post by the way well done Wcch gets it done those flow numbers are crazy
Last edited by z0sicktanner; 06-26-2013 at 05:22 AM.
#20
Melting Slicks
Member Since: Apr 2009
Location: Virginia Beach VA
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C2 of the Year Finalist - Modified 2020
C2 of Year Finalist (performance mods) 2019
I had my car done by Vengeance in February with the Stage 2 heads and tune. I also did the Halltech 103 cai. I dropped the car off Monday morning and picked it up Tuesday afternoon. The price was the same as the quote with no surprises. They have a very professional staff and they even washed my car for the ride back to Virginia Beach. 100 percent satisfied. Why go to stainless values, because they are stronger than the sodium filled, cheap and they work. BTW, my buddy Andy dropped his car off at the same time and the did both cars together. I doubt some dealerships could do that.