Originally Posted by lakeroadster
I had the same set-up you are describing on my Model A when I first built it. 1972 era 355 sbc (no road draft tube), intake mounted oil filler with breather, no breathers in the valve covers (corvette aluminum finned covers). I ended up using a cotton filter on the breather due to blow by, to keep oil drops from splattering on the body.
Worked great until after about 300 miles, the first time I ran the rpm's up to about 6,000. It blew the seals out of the fuel pump and puked oil all over the header. I thought for sure I blew up the engine, based on all the smoke I saw in the rear view mirror.
I rebuilt the fuel pump (Holley) and then installed a moon breather in the driver's side valve cover. I then installed a '67 Corvette oil filler tube (with a pvc valve port) in the manifold, installed a pcv valve, and used a cap instead of a breather on the filler tube.
I haven't had any issues since, no more drippy oil blow by issues, no more blown fuel pump gaskets.... it's been troubble free for the last 9 years.
Hope my experience is helpfull to ya!
My '56 Chevrolet had Corvette valve covers and a aftermarket breather arrangement as shown in the photo. The aftermarket breathers were mounted in the sides of the valve covers so the rocker arms would not flood the breathers with oil. I had a 1965 Chevrolet FI 30-30 solid lifter camshaft and the lifters would shoot oil over the fenders when I was adjusting the valves. I finally stopped the excessive rocker arm oiling by using 1965 Chevrolet edge-orifice solid lifters that restricted oil flow to the rocker arms. The GM edge-orifice lifters also saved my rod bearings!
The 1962-1866 Pontiac engines had problems with oil blowing out the valve cover breathers. The Pontiac 421 HO and SD engines had baffled valve cover stacks in each valve cover that were about 4" high. That was a fruitless attempt to prevent oil from blowing out the breathers at high RPM. The passenger side breather stack was in the middle of the valve cover, between the rocker arms and it did not throw oil. The other breather was in the front of the driver's side valve cover, directly above a rocker arm. That was the breather that blew oil all over the firewall. I reduced oil blowing out of that breather stack by pushing a piece of foam rubber down the stack and eliminated oil blowing by pushing a piece of rag down the breather stack. . I have even seen Pontiac owners at the drag strip wrap their breather stacks with a rag to prevent oil blowing. .
Where you put those valve cover breathers makes a difference. Do not put them over a rocker arm. The oil blowing problem was finally solved when GM went to the closed PCV system in 1968.