Help-- discreet PCV for small block Chevy

YES- I've already done a thread search, and I'm still having a little trouble figuring out some specifics. Please chime in if you are so inclined:

I want to run early style (solid) script valve covers and an intake with a front oil filler tube- BUT on a motor without provision for a road draft tube (1973 400sbc).

1) The plan so far is to use a front oil filler tube with a hose bung, and install a PCV valve hidden under the air cleaner, connected to the carb.
Does the oil filler cap then have to be vented? (even though ventilation circuit is drawing from inside the motor and into the carb)?

2) Then where should the actual vent/ breather be located?
Opposite end of the crankcase (from the oil filler tube) would seem most logical, but the problem remains- no road draft tube.

3) Is there a simpler way to do this?


***By the way, I have a brand new pair of fully polished Cal Custom style valve covers and Performer 2101 intake if anyone would like to trade for something more period specific ('62-'68 SBC)

 

The PCV under the air cleaner will serve no purpose at all. You can get one that threads into the back of the carb I dont know the PN# off hand, then run your line from the filler tube.

 

You still need an air intake located somewhere at manifold level. You could hide one on an intake plenum/runner. I have also seen old vette setups (midsixties)where there is a threaded deal for the PCV...maybe check out a vette resto catalog.

 

Pretty much what i was describing--by "hidden under the air cleaner"

Doesn't it still need a vent or breather to draw air INTO the motor?

 

Yes, you need an air intake....

 

I guess that's the way in which a modern PCV system works, right?-- drawing pressure through the piston ring / cylinder wall seal (valve cover-to- valve cover). Weird.

 

Thanks

 

This is the factory setup for 1969. You can move the various components but keep the same theory of the flow.

 

i've seen people drill holes in the back of the block betwwen the intake and the bell housing flange. go to www.corvetteforum.com and do a search. someone posted some pics there. if i get time i'll try to post a link.

 

You can hide the PCV anywhere that you can get access to the top of the crank case. I used the area between my carb and distributor (SBC). Drilled a hole and used a rubber grommet. Some guys have threaded them in using the thread in type from Mazdas (?). Then you can use your oil fill tube as a breather.

Here are some informative PCV posts:

http://www.jalopyjournal.com/forum/showthread.php?t=31741

http://www.jalopyjournal.com/forum/showthread.php?t=64338&highlight=PCV+valve

http://www.jalopyjournal.com/forum/showthread.php?t=265049&highlight=PCV+valve

 

NICE!!! Thanks, you guys.

 

Maybe a dumb question: But if you use a front fill tube why would you need the PCV valve? I only ask because all the fill tubes I've seen have a cap that's also a breather.

 

Drill and tap (NPT) a spot on the intake that directly accesses the lifter valley. Go to Autozone and get a threaded PCV valve. Screw it into the manifold, hook it to the appropriate nipple on the carb and you've got it. Your open breather on the oil fill tube will be fine.

 

Here are are a few photos of my PCV. Don't forget to put a baffle over the open hole. A plate will do.








Ago

 

I did a deal similar to Ago except that I have an air-gap intake so I ran the hose under the carb to the pcv that is threaded into a hole directly under the center of the plenum. On the valley side of the intake I drilled and tapped it for machine screws and attached a baffle cut out of an old valve cover. I wasn't concerned with where to draw in outside air so I'm using vave cover breathers but I can't see why the old style oil filler tube with a breather cap wouldn't work. It would set up a short path of air movement from the front of the engine to the middle of the intake which probably isn't ideal but better than nothing.

 

If your rings are sealing properly, the front oil fill tube with an open, filtered cap is all you'll need

 

No, it isn't. but there is no sense in arguing with ignorant people.

 

GOOD, I hate a battle of wit with an un-armed man/girl

 

Seconded. You will blow an oily sheen out of your breather at higer RPMs (like, 2000) if you don't have a PCV to help regulate. I know cuz I done it.

 

Not according to some people.

 

Sure, if you have poor "ring seal". Like I said, "IF" you have good ring seal.......................
If yours is blowing out an oily sheen at a mere 2000 RPM, your motor's "done". Stick a fork in it

 

I have the pcv plumbed into a baffle underneath the intake filled with copper chore boy. It is connected to the rear of the center carb. The return air is suppose to be the oil fill tube breather cap. When at highway speeds, it spit oil out the cap, not a lot, but it spit it on the windshield. So, I welded a tube with another baffle (more chore boy again) on the bottom of the cap that fits snugly into thetube and machined a groove for an O ring in it. That ended the oil spitting. Now I get a bit of oil at the rear of the intake and the dipstick tube. What am I missing?

 

There is a filler cap which has a hose barb on it. You can connect the hose to a filter in the air cleaner like an OEM setup. The spit up oil will then be ingested thru the carb.

 

The purpose of a PCV is multiple: It helps ingest blowby from the crankcase to run it through the combustion cycle again, which keeps the crankcase pressure from putting oil vapors out of your breather, it promotes better ring seal, it keeps your oil cleaner and your engine sludge free by burning off water condensation vapors out of the crankcase. Perfect 100% ring seal is not attainable in any engine, let alone a daily driver. Its a cheap modification that makes sense and keeps the air cleaaner that you breath when you are sitting behind it going down the road.

 

No you're not drawing pressure from anywhere. You are simply removing the blow-by gasses from the engine. This is done by creating a slight draw through the engine, using the vacuum of the intake manifold to pull the bad stuff out via a PCV valve, and also drawing some clean (hopefully) filtered air in through a breather of some type. If engines aren't vented, they really get nasty inside.

Groucho, No such thing as a perfect ring seal, there's ALWAYS some blow-by. I've never seen a traditional auto engine that didn't have both a place for the bad air to get out, and the good air to get in. There are variations of ways to pull the bad out, whether they be a draft tube, PCV arrangement, or even scavenging via a venturi tube on a header. If you just run an oil fill tube with a breather cap, with no provision for creating airflow through the motor, you're going to have a sludgefest to deal with when you tear it down.

 

For what it's worth I've heard of people drilling a hole in the end of the valve cover, towards the firewall, and mounting the PCV there. Not invisible, but pretty discreet.

 

On my situation, maybe I should try the hose or line from the oil fill tube to the bottom of the air cleaner for the return. Then, seal the oil fill tube, and I should have a closed system similar to OEM. With it set up as it is now, I don't understand why I have crankcase pressure putting oil out the dipstick tube and the back of the manifold. Not a lot of oil, but I shouldn't have any. Any ideas? I have been reading threads on this subject for a year now, and still haven't solved my problem. I had another pair of Cal Custom valve covers milled for Moon breathers for long highway trips and wipe the engine down often, but that's not the fix I am looking for. Any help would be appreciated.

 

No, you guys don't get it. If there's no place for crank case pressure to go, it'll come out where ever it can, which was the breathers in my case (yes there's a foam element in them). A Positive Crankcase Ventilation valve fixed all that.

I mislead you when I said 2000 RPM. I should have said "This isn't a race car and I don't push 6000 with it, the oil vapor will come out of the breathers under normal driving conditions." I figured you'd know what I was talking about.

 

What is wrong with this set up? I have a pcv connected to the crankcasw or valley, it is connected to the center carb, there is an air return thru the oil fill tube. Is the return too large?

 

On the engines that had a fill tube and breather cap up front, remember that they also had a road draft tube behind the distributor. The vapors got pulled out the back, and fresh filtered air came in the front. If you remove the draft tube and just use the front breather, the engine will build up pressure and it will push itself out the breather, making a mess as described. It will happen regardless of the engines condition, the only thing that will vary is the amount of stuff that comes out.