Stage II LS7 cylinder heads - A visual guide to valve guide wear and CNC upgrades

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06-25-2013, 10:34 AM

David@Vengeance

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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:

Quote:

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....

Many enthusiasts have been looking a proactive approach to fixing the issue, which always results in removing the cylinder heads. Here at Vengeance, we see this as a perfect time to upgrade the already awesome LS7 units and the majority of our customers agree. But first, let's look at a quick and dirty way to determine irregular valve guide wear. This is NOT the best way to preform this work and we have every guide checked by our cylinder head machinist using a specific valve guide bore gauge, but most people don't have one of those. So, for the do-it-yourself mechanic, this is an easy way to check heads on the bench.

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.

Stage II LS7 cylinder heads - A visual guide to valve guide wear and CNC upgrades

Stage II LS7 cylinder heads - A visual guide to valve guide wear and CNC upgrades

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