I had my 454 professionally rebuilt a few months ago, and went with all new heads, carb, etc. I'm getting oil leaks at both the front and rear main seals. Nothing dramatic, but more of a leak than is justifiable on a brand new motor. When I called the shop about it, they said leaks there are almost always the result of inadequate crankcase venting, which then causes too much pressure in the crankcase. When I reassembled with all new parts, I ran a vent on one valve cover, and a PCV valve on the other valve cover. I ran the hose from the PCV to the base of the carb, thinking that would give me constant vacuum. The shop says I should run the hose into the air cleaner instead. They say that running into the carb base effectively creates a "closed loop", and doesn't provide enough venting. Any opinions? How are the hoses for the PCV routed on stock motors? Any help will be greatly appreciated.

The oil leak may well be from too much crankcase pressure, an indicator of no PCV or a plugged PCV. Get the biggest PCV you can find and try it, should be connected to the large port at rear base of carb.

I've never seen it on the air cleaner, always at the base of the carb. Not that it hasn't been done - I've just never seen it there. Stock location is at base of carb - otherwise your air cleaner will quickly get a thin oil coating.

Even at WOT, when manifold vacuum is near zero, you would still get a siphon effect from the base of the carb.

While I'm no expert, I think the "Closed loop" thing is a bunch of crap. The air going into the air cleaner is the same air going through the carb and into the engine.

The "close loop" thing would be a connection from the air cleaner to the valve cover instead of a separate breather in the valve cover. Typically, there would be a little filter element inside a small plastic holder inside the air cleaner. The PVC would still be in the other valve cover connected to the carburetor base as you have it. This became the factory set up in the 70's and remained up through the era of throttle body injection in the late 80's. Changing to this arrangement won't solve the problem you have, using a larger PVC as suggested is the thing to do.

More people out here should look into the "Offenhauser" valve cover
breathers. They have one of the best setups out there. They're a little on the expensive side and a little involved to mount, but they do work. The part number for the top mounts is 5409 and the side mounts is 5410. We use many of the 5409's. If there's no major problems (internally) with the engine, these breathers will totally eliminate the need for any PCV system, which in turn prevents pulling oil or oil fumes into the plenum. And the "bigger" the motor, the better they work. They are available with or without any "name" on the top in case there is an issue with the brand. Thanks, Gary in N.Y.
P.S. They measure about 6.000" long and 2.000" wide and have "washable" inserts. They also actually add to the engine appearance, having a polished finish. I think it's been about 20 years or so since we built an engine that used a PCV system, maybe longer.

My '65 has a "fixed orifice" crankcase ventilation stock. The fresh air to the crankcase is a tube from filtered air in the air cleaner to the oil filler which is a metal tube projecting from the intake manifold. The blowby and other gases and vapors are extracted through a tube which runs from a fitting at the back of the block to a fitting at the base of the carburetor which has the fixed orifice. Its early PCV before "PCV valve".

Seems to me that what the shop told you is nonsense...But just my $0.02

p.s. I think its against the law to disable PCV. Also kinda dumb. Again one man's opinion.

Are you getting leaks at the main seals or at the front and rear of the oil pan?

Eric,
I can't see any leaking at the sides of the pan, just at the front and rear. I'm not sure if it's actually the main seals or not. The front appears the be leaking at the bottom of the curve in the pan, but I can't see the rear very well. Would that lead you to assume something different than the mains? Thanks.

Gosfast: Thanks for the idea. Are two required, or would one be enough? I'm planning to re-install my A/C. Is there room for A/C and one of these, or would one be enough to vent the motor? Thanks

Gosfast: Thanks for the idea. Are two required, or would one be enough? I'm planning to re-install my A/C. Is there room for A/C and one of these, or would one be enough to vent the motor? Thanks
One in each side is recommended and I'm sure there would be no "room" problem. They really do work excellent. If you like you can place a call out to Offenhauser (323-225-1307) and ask for Tay or Vince, they'll be glad to help. Thanks, Gary in N.Y.

Rick;

So it sounds like it may not be leaking from the mains, but possibly the front and rear of the oil pan? If the oil is coming from the area between the pan and the block it is possible that 1) you installed the pan without properly sealing it, or 2) you installed a thick gasket pan with a thin oil pan gasket. There are actually two different kinds of pans. One uses a thick gasket and the other a thin gasket. If you got an aftermarket pan or mix-matched pans it is possible that this it the cause of your leak.

I am not sure of the exact dimensions at the front and rear of the pan...or the change-over year ect., but I am sure someone will chime in.