Crank Case vent old 350 block

[namredla]

Anyone ever run into a crank case vent setup like this? PCV / breather attached to the top would just run to manifold vacuum? That simple?

[raggedjim]

Ok, I have a couple of questions.

Do you fill the oil by removing the cap with the fitting on it? I'm guessing there is a tube going down into the lifter valley behind the thermostat housing.

Does the cap have an internal pcv? Or is it designed to be a closed breather that pulls clean air from the air cleaner?

If it is a pcv then where is your fresh air going to come into the crankcase?

If it is a breather where does your pcv go?

Is it a combination pcv/breather??? I have never seen one if it is.

Is there a road draft tube? If so the the cap should be a breather style. It can be a simple breather or one that is closed and pulls clean air from the air filter. (like one you have shown).

Nice looking engine.

Rg

[Willshook]

It's just a vent; tube goes into the cam valley - not to manifold pressure.

Serves the same function as a PCV, but dumps into the air instead of into the intake to reduce emissions. I think they switched in '68 or so.

Pull the cap off to add oil.

[namredla]

I appreciate the input. It is the oil fill, and the cap / breather at the top is not a PCV type (although I think they do make one that is). Here is a pic of the tube going through the manifold, I'm thinking this was not an option but was cut in?



So thinking this through, it would make sense to run this to the air filter, at least in my mind. If that's the case, then where would I pull a vacuum to the crank case with a PCV valve? This would be my manifold vacuum port by the dizzy:



Is there a port where I wouldn't pull a bunch of oil out as it splashed around? Is there a need run a PCV system at all, or just a filter on the end of that breather? This would have been just a draft tube originally, and I would normally do all of this through the valve covers.

Thanks for the help.

[Willshook]

If someone wants that "vintage" pre-'68 look, then it's common that they'd machine a hole for the tube. Some intakes even have a pad to mill the hole out.

There's no need to make any changes to what's there unless you feel the need. PCV is an *emissions* device; it has no impact on the engine's ability to run. That cap already should have breather holes around the circumference so it's not just a solid cap. I expect it's this standard-size breather...

https://www.summitracing.com/parts/e...8aAhqdEALw_wcB

That fitting in the pic looks like it also goes to the cam valley and not to manifold vacuum...

[raggedjim]

Well I kinda like running a pcv.

Here's what I did on my intake (Performer). The hole is drilled into the valley and I used a baffled grommet for the pcv. The vacuum for the pcv will come off of the carb.

It looks like you are using a RPM Airgap intake?

[raggedjim]

I'm with willshook, this looks like it is going into the lifter valley.

Did you buy this modified this way? It looks to me like someone modified it.

[namredla]

It is an RPM Airgap. The engine was purpose built by a local, well known and a stellar reputation, but has been sitting for a bit. I'm stumped at the port by the distributor, I don't know why there would need to be another path to the valley seeing as how it is covered with the breather. I agree though, it is in the wrong place to be vacuum (maybe he was intending on this to be a draft tube). I have always run PCV as well, just feels like it keeps things a little bit cleaner. But, that is a decision that can be made after I have everything put together.

Looking around, I see some guys running a water bypass from front to back? Is that to provide more uniform cooling?

[Willshook]

Originally Posted by namredla

Looking around, I see some guys running a water bypass from front to back? Is that to provide more uniform cooling?

Racing engines often run AN lines between the front and rear cooling passages on each side to equalize cooling and maximize flow. I’m not confident there’s a real benefit, and certainly none for a street engine.

[raggedjim]

I think I'd ask the builder if he is still around. My guess is he was going to use that connection to go to a pcv valve to pull out crankcase gases.

The only water bypass I'm aware of is on LS engines and some of the hotter circle track cars. I'm not sure a 1st gen smallblock really needs it.

[namredla]

Yeah, that makes sense to me. The only thing I don't understand then is if the oil fill and added port at the back both tap the lifter / cam valley, then am I really evacuating anything out of the crankcase? Is seems like I would pull a draft right across the top of the valley and any blow by would largely remain below. Maybe I'm splitting hairs here....

It makes sense in a valve cover to valve cover PCV like I am used to as that would draw a u shape from left to right. The system in my build seems like it would draw a straight line from from to back right under the manifold.

[Willshook]

Originally Posted by namredla

Yeah, that makes sense to me. The only thing I don't understand then is if the oil fill and added port at the back both tap the lifter / cam valley, then am I really evacuating anything out of the crankcase? Is seems like I would pull a draft right across the top of the valley and any blow by would largely remain below. Maybe I'm splitting hairs here....

It makes sense in a valve cover to valve cover PCV like I am used to as that would draw a u shape from left to right. The system in my build seems like it would draw a straight line from from to back right under the manifold.

It's important to be clear on how this system works in general - there's no need to apply vacuum to remove blowby. The tube and the cap will be just fine to vent the internal blowby overpressure overboard. Just put a regular cap with no host tap on it and be done.

Again - the PCV isn't doing anything other than routing combustion gasses into the intake to be burned again as an emissions thing - it's not needed in any way. I mean, hug a tree and all that - but it's not doing anything to add power.

I'm honestly kind of lost on this interest in having a PCV if one isn't required.

[namredla]

I hear you Willshook, I'm not trying to hug any trees, and if I don't need a PCV then I'm happy. I just want to try to understand the system, and the yardstick that I'm using to measure against is one that has always included a PCV, and I guess old habits are hard to break. If anything, it always felt like a way to keep things a bit cleaner, but maybe I'm just wrong (it does happen from time to time to time to time....).

I do appreciate the help and feedback.

[raggedjim]

For me, and I'm no expert, all of the engines I've had with pcv seem to stay cleaner. Every engine I've had without them always built up crud in the heads and valley. Not sure why but that is why I tend to run them.

[Willshook]

Originally Posted by raggedjim

For me, and I'm no expert, all of the engines I've had with pcv seem to stay cleaner. Every engine I've had without them always built up crud in the heads and valley. Not sure why but that is why I tend to run them.

Crankcase blowby is crud, so I get the desire to remove it - but I personally haven't seen that big of an impact to PCV over just well-vented.

But certainly no harm in running one either, and if that's been your experience then it's all good