Fixing Oil Sucking on LS1 Engines with Holley Valve Covers: The LS6 Valley Cover Solution

If you’ve installed a set of Holley valve covers on an LS1 (such as in a 2000 Camaro SS) and noticed oil being pulled into the intake or heavy oil and fuel collecting in your catch can, you’re dealing with a very common issue. The Holley covers look great and often provide better clearance or coil mounting, but many aftermarket valve covers lack the effective internal baffling and PCV integration that the factory design uses. This allows more oil mist to be drawn into the intake under vacuum.

Chevrolet improved this on the LS6 (and later engines) with a redesigned valley cover that does a much better job separating oil from crankcase vapors before they reach the intake. Upgrading to an LS6-style valley cover is one of the most effective and affordable fixes for this problem

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LS6 valley cover (shown with gasket and hardware). Note the dedicated PCV tube outlet and improved internal design.

Why the LS6 Valley Cover Works Better

The PCV (Positive Crankcase Ventilation) system vents pressure and oily vapors from the crankcase back into the intake so they can be burned instead of building up pressure or venting to the atmosphere. On early LS1 engines, the valley cover is a critical part of this system. The LS6 version has better baffling and routing, which significantly reduces the amount of oil that gets pulled through.

You can find these covers on Amazon, eBay, or performance parts sites (common GM reference around part 12577927 or compatible aftermarket versions). Many builders pair it with an external oil separator / catch can in the PCV line for even better protection.

The Required Modification: Grinding the Block Boss

On 1997–early 2000 LS1 blocks, there’s a small, non-functional casting boss (a raised aluminum protrusion) in the lifter valley that prevents the LS6 valley cover from sitting flat and sealing properly. This boss serves no purpose on the LS1 and is easily removed.

ls1tech.com

LS6 Valley Cover Swap - LS1TECH - Camaro and Firebird Forum Discussion

The area to modify — arrow points to the casting boss that must be ground flush for LS6 valley cover clearance.

Safe grinding procedure:

1. Remove the intake manifold for full access to the valley.

2. Cover and protect every opening — intake ports, lifter valley passages, cam area, etc. — with rags, tape, plugs, or plastic sheeting. Aluminum debris can cause major damage if it gets inside the engine.

3. Use a Dremel, cutoff wheel, or die grinder to carefully grind the boss flush (typically removing material to about ¾" depth or until the cover seats properly). Work slowly — aluminum cuts quickly.

4. Thoroughly vacuum the area, then clean multiple times with brake cleaner, compressed air, and lint-free cloths. Inspect carefully before reassembly.

This is a permanent but straightforward modification that thousands of LS builders have done successfully.

High Compression and Remaining Catch Can Contents

Even after this upgrade, you may still see oil and gasoline collecting in your catch can — especially at 12.5:1 compression. This is normal and expected.

Here’s why: Higher compression creates much greater peak cylinder pressures. Even when compression and leak-down tests show excellent ring and valve sealing at rest, some combustion gases still slip past the rings into the crankcase during actual operation. This is called blow-by. These gases carry oil mist and unburned fuel vapors. The PCV system pulls them out, and a good catch can traps the liquids before they reach the intake.

Your catch can is doing exactly what it should. High-compression performance builds simply produce more of this mixture, particularly under load or during spirited driving. Empty the can regularly (more often after hard runs), and consider a larger or multi-stage baffled separator if it fills quickly.

Summary of Benefits

• Dramatically reduces or eliminates oil being sucked into the intake.

• Improves overall crankcase ventilation and reduces sludge risk.

• The LS6 valley cover + catch can combo is a proven, cost-effective upgrade used across the LS community.

• Your existing Holley valve covers can stay on — you’re just improving the critical valley/PCV portion of the system.

This modification brings the PCV system closer to the more refined design Chevrolet used on the LS6 and later engines. It’s one of the best “bang-for-buck” improvements you can make on an LS1 for cleaner, more reliable operation.

If you’re running Holley (or similar aftermarket) valve covers and fighting oil issues, the LS6 valley cover with the minor block modification is a reliable, well-documented solution.

Ready to publish. Just copy everything above (including the image placements). For your own site or posts, download the images or use clear photos of the LS6 valley cover and the block boss area — they make the guide much more helpful. Let me know if you need a shorter version, first-person tweaks, or anything else adjusted.