Crankcase evac. Question?

There SHOULD be a one way check valve at the collector.

Also, the angle of the tube that goes into the collector is important, as is how far that tube goes into the collector.

I've seen as high as 8 inches of vacuum on a 632 Chevy at 7200.

Most I've seen on a small block was mine at 6 at 8800.

I haven't had one back up yet. But...when using alcohol I changed the check valve ever 75 runs or so. They would get a build up on them and not shut. I learned that the hard way.