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breather box, valve cover vent, and hose routing observations
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esde
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Joined: October 20, 2007
Posts: 5927
Location: central rust belt
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PostPosted: Mon Aug 21, 2017 7:45 pm    Post subject: breather box, valve cover vent, and hose routing observations Reply with quote

Wanted to take a few minutes to share some observations I've made over the past few months. After not driving my car for several months, I dusted it off and took it for a spin. 2 liter, efi, both valve covers vented to the bottom of a CB oil fill mounted box like this one
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I have the vent lines run to the very bottom of the breather box, and the box cavity packed with stuff to collect the oil vapor before it blows out the little filter on top. Generally, it worked well, or so I thought. With the EFI the car runs so strong, that I've been flogging it in the upper rpm range a good bit more because it's a blast. And the breather is not up too the task, the top filter gets soaked with oil, and it drips and makes a mess. At mid rpm, there is a pff-pff-pff at the top vent on the box.
A few weeks ago, I had one of the valve cover lines come undone, and melt on the header. Lotsa smoke, and some panic. Then, with not enough hose to connect both covers to the breather, I blocked one and left the other connected. The pulses out of the breather were stronger than with both connected. Tried switching which valve cover was connected, same thing. Neither cover (one disconnected, the other pinched off) and it was maybe better, but still pfff-pfff-pfff at mid rpm and a wet breather after some fun driving.
Here's when I found the right combo for this engine, I connected both valve covers together with a tee fitting, and ran the other leg of the tee to the breather at my distributor plug.
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no more pfff-pfff-pfff, and no more oil puking breather box. I have only the fuel pump stand connected to the CB breather, and am going to try disconnecting it. My theory is that the without a valve cover vent, the oil doesn't drain as easily from the rocker box, much like pouring a can with only one hole punched. But, venting the cover to the breather sent too much oil up. Just connecting each cover back to the top of the crankcase seems to have let the pressure stabilize, or however you'd describe it. Anyway, it's working for me, and thought I'd share it.
SD
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bugguy1967
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Joined: January 16, 2008
Posts: 4338
Location: Los Angeles, CA 90016
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PostPosted: Mon Aug 21, 2017 8:21 pm    Post subject: Re: breather box, valve cover vent, and hose routing observations Reply with quote

I see what you did, but I find that the oil drainage isn't a concern unless you don't have a sump. Let the oil fill in the covers, and vent from various points on the crankcase. If you're a circuit racer or drag racer, this may not apply, but for street engines that see periodic higher rpm, it shouldn't be a concern.

A faster way to get oil out of the rocker box is to add a big -10 drain straight from the head to the sump.
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