PCV Valve 347 Stroker Plumbing

[Jeff10]

Hi Everyone,

I've read a few threads that are close to what I am needing help with. There are a couple of differences that I should explain.

The motor in question is a 347 stroker. It has a Holley Truck Avenger carb setup.

The previous owner installed a PCV valve toward the back of the passenger valve cover without connecting it to anything.

I purchased an aftermarket Holley air cleaner assembly complete with knock-outs in the base.

I believe that what I have been reading is that the PCV valve should be plumbed to the base of the carburetor or intake. Or, should it be plumbed to the base of the air cleaner?

If plumbed to the carburetor I'm assuming the tube ID connecting the two should be 3/8" ID to match the connector on the PCV valve. If attaching to the air cleaner the choice isn't so clear as the elbow provided with the air cleaner is .70".

And maybe while I'm asking for help, it might be good to confirm the correct PCV valve. The valve that I pulled from the valve cover is a 3133216. I don't really come up with anything when I Google that number, though. I'm not sure if it is sized for the 347 or the 302, or if it even makes any difference.

Thanks to anyone who has been through this same thing.

Jeff

 

[BOBS 2 68S]

My PCV is connected to the large port on the back of the carb.

 

[Jeff10]

Hi Bob,

Thanks for the reply. I probably should have done my homework better before posting.

I found a Holley Truck Avenger 670 manual online and found the port they identify as the PCV port. Just as you said.

The next step is going to be understanding if anything needs to be connected to the base of the air cleaner. Breather cap for the valve cover on the driver side? Or, no connection necessary.

Thanks for your reply.

Jeff

 

[EPB72]

It depends if you have emissions testing and requirement of your state ,,, a closed system breather to filtered side of air cleaner ,, or open system has a filtered cap just on the valve cover…. Plus on one valve cover and breather on opposite valve cover..

 

[DirtDonk]

The point of the ports on the bottom of the air cleaner OR the filtered breather cap is to allow clean, filtered air back into the engine as the PCV valve sucks out the bad air.
When "dirty" air is pulled out, something else has to go in and take it's place. Since we don't want dirty crap getting inside the engine, a filter is used. The factories used the easiest, cheapest (and likely the best) source available, which is from inside the air filter.
Filtered caps were designed to take the place for those that either did not want to plumb it to their nice new air cleaner setup, or could not figure out a clean way to do it. Some filters just don't lend themselves well to that.

If everything is working as expected, then either the main air filter or a filtered cap on the valve cover will work just fine. In the real world the filtered caps often get oily and make a bit of a mess on the valve cover.
But they're easy enough to clean or replace, so it's not a deal breaker.

For the vacuum side, yes the valve matters, but I don't know how to best determine what's best for what engine. Typically you end up putting in what was originally called for in a performance version of your engine. Say a Mustang 351W of about '70-'71 vintage maybe?
That question is why a company finally came out with a PCV valve that you tune you your individual engine's characteristics. Instead of $10 bucks, it's more like $100 bucks, but it's the cat's meow of PCV valves.
I'm sure someone will have a link to the manufacturer. It was posted up again just a few weeks ago and I forgot their name. Again!

The 3/8" hose is usually correct for aftermarket carbs and the typical PCV valve. For most (if not all?) year Broncos Ford used a vertically oriented valve with a molded rubber hose to mate it to the carb spacer. Molded to make sharp curves and molded to fit the larger opening on the spacer. With the Holley carb you can fit 3/8" hose to the carb and valve, but a new valve with a 90° fitting on it makes it a bit cleaner with fewer sharp bends. So when you can find one of those with the proper rating, you can save yourself some hassle.
Looking for one to fit my '71 was how I discovered the wide discrepancies between valves. One for a '73 Granada with 302 and one for a '70 Corvette with 350 looked identical, but only the one for the Corvette would work with my 302. The one for the Granada acted like one huge vacuum leak and the engine would hardly get out of it's own way when you tried to accelerate.
Maybe some extensive carb tuning would have cured that issue, but instead I just used the one that made it run better. In theory it still did the job, but my next one is going to be one of those $100 beauties!

And even though some engines and some diagrams do show the PCV valve plumbed into an intake manifold runner, for our engines that is absolutely incorrect. The valve vacuum MUST be sourced from a common plenum area of the intake. Either at the base of the carburetor, or a carb spacer, or the intake itself but from a common area where all 8 runners can share the duty. Not just one cylinder.
It's ok to plumb the power brake booster into a single runner, but not the PCV valve.

Paul

 

[Jeff10]

Hi Guys,

Not sure why I'm not getting notifications... I think I have my profile set up correctly. Anyway, sorry for the late reply.

I ended up buying a PCV with a 90 built into it. It is now connected to the PCV fitting on the Holley.

There is a filtered breather cap on the driver side valve cover. For the time being I will just stick with that. I'm just trying to clean things up in preparation for getting it running again. Once it's running, I may plumb it to the bottom side of the air cleaner.

Thanks for all the comments here.

Jeff