GM's replacement PCV valve for low manifold vacuum 12572717 is also made by other companies such as BWD

GM’s replacement PCV valve for low manifold vacuum part number 12572717 is also made by other companies such as BWD

Recently I replaced my tired old Inline 6 cylinder in my 1963 C10 with a used 350 crate motor. The previous owner has put a fairly ‘large’ cam in it, and it has that aggresive ‘lopy’ idle that we all want. While it sounds great, cams like this create very low vacuum at idle, which introduce other problems.

Chances are that if you are reading this post, it is because you are having a hard time finding a PCV valve that will operate correctly with low manifold vacuum. Try using a standard PCV valve with low vacuum, and you can hear an annoying clicking or ticking noise. This is caused by the valve not fully opening as there is not enough vacuum to do so. This may create other problems as you may not be extracting all the crank case gasses building up in the engine, which the PCV was designed to do. While there are a few options out there to solve this problem, I was surprised I was never able to find a specific ‘high performance’ or aftermarket PCV valve for low manifold vacuum motors. Most people recommend getting a PCV valve from an early to mid 60’s high performance car, such as the corvette which came from the factory with low manifold vacuum.

Upon further research, I discovered that not many years ago, GM released a PCV valve … which isn’t really really a valve at all. It’s just the PCV housing, with all the guts removed and is hollow in side. The bottom side has a pin hole, much smaller than standard PCV valves. The GM part number for this PCV is 12572717, and you’ve probably seen this referenced all over the internet while doing your search. I went to my local Advanced Auto Parts store, and while they didn’t have the GM brand, they did have the exact same part made by a company called BWD, and it is part number PCV484. It cost me just under $8, and made a huge difference in my motor. Because the inlet hole is so small, it actually helped bump up my manifold vacuum, and now I feel safe that the crank case gas build up is being removed safely with out me having to worry about. It fits right into my Chevy Small Block 350 as any PCV would do.

Here are a couple more photos of this PCV valve

BWD PCV484 is a replacement for GM 12572717 and is available at Advanced Auto

BWD PCV484 is a replacement for GM 12572717 and is available at Advanced Auto

As you can see, the inside is completely hollow. The valve part of the PCV has been removed, and air flow is restricted by the pin hole inlet at the bottom

As you can see, the inside is completely hollow. The valve part of the PCV has been removed, and air flow is restricted by the pin hole inlet at the bottom

Here you can see how small the PCV inlet hole is. This restricts the air flow, helping boost your manifold vacuum, but still allowing the intake vacuum to suck up crank case gasses.

Here you can see how small the PCV inlet hole is. This restricts the air flow, helping boost your manifold vacuum, but still allowing the intake vacuum to suck up crank case gasses.