PCV for low vacuum camshafts?

[drdano]

Hello gurus. Is there a part number floating around out there for a PCV valve that works better with engines that make low idle vacuum. Google searches say a Fram FV181 (supposedly number for a Boss 302 motor) works better at low rpm. I have 244@50 .663" lift cam in my 428 and the best vacuum I can get so far is 10" at idle with 750 DP carb. When I pull the pcv and block it with my finger, the idles drop 200+ rpm, which makes me wonder if the pcv is opening fully at idle (due to low vacuum) and shouldn't be. Anyone been down this path before have some advice on a better PCV number to try? Thanks all.

[jayb]

This isn't really answering the question, but my preference would be to ditch the PCV.  Any oil mist entering the intake will make the engine more prone to detonation anyway.  If you want to keep the scavenging effect to go a crankcase evacuation setup where the valves are located in the collectors.  This will aid in horsepower production and also eliminate the possibility of oil mist in the intake tract.

JMO - Jay

[afret]

Yeah, crankcase evac works well but you need to use straight through low restriction mufflers.  Didn't work with reverse flow mufflers even the large bodied 3" Dynomax turbos. 

If you want to keep the PCV, make sure you limit the mechanical advance in the distributor so you can  run a lot of initial advance and also run a bit higher idle RPM to try and get higher engine vacuum.  The crankcase evac is the way to go though.

[My427stang]

I am going to throw out a different opinion

Just off idle, part throttle, you'll have plenty of vacuum
WOT, regardless of the cam, the PCV isn't doing anything

So the last situation is idle, you arent building much crankcase pressure, so why even worry about it, just make sure its a large enough line to pull some negative pressure and take away the moisture not pressurize anything

The trick though if you want a little more at WOT, run the other breather back to the air cleaner, like a new car.  That way when vacuum goes to zero, some venturi action from the air rushing into the carb will pull on the other side.

Like Jay said, you run the risk of some oil contamination, but you could also run a break box, sort of a drainable plenum if you are pushing oil, like the diesels do.

I haven't had any issues, or noticed any difference with any PCV.  I see the topic come up now and again, but have always just grabbed a 3/8 90 degree for all mine, and even when I swapped PCV as this topic came up, I could never tell the difference

[drdano]

Lots of different answers here, thanks for the comments.  When the engine is warmed up, there is a lot of PCV fumes at idle.  If I disconnect the hose it pours out of the 3/8" line pretty heavily, out the dipstick and out the opposing breather side as well.  This is a new motor that isn't broken in yet, so maybe it will be better once it has?

So, if I pipe direct to my header collector, I assume I'd need to do this on both sides?  With an RPM intake, where would the fresh air enter the motor if both breathers go to the exhaust?  Or, would I run an open breather on one side and the opposing side to the collector?  How is my 02 sensor for my AFR computer going to react to this?

[My427stang]

Well, generally leak down numbers are pretty good right off the bat.  If you are pressurizing the crankcase now its not really a good sign.

Was it a re-ring or a new bore?

[drdano]

New everything.  +30 overbore to clean up the cylinders, new forged TRW pistons, new rings, etc.  So, there shouldn't be hardly any PCV fumes at idle? 

[My427stang]

There shouldn't be much coming out of there

Sometimes after sitting for a while, humid conditions, it may steam as it burns off any moisture, but you shouldn't have any significant volume/pressure being pushed out.

Any way you could make a movie of it?

[drdano]

Well crap.    

I can shoot a movie in the next day or two.  There is no vapor on startup, but after 5 minutes if you pull the PCV from the breather, it pours out the breathers and some comes out the dipstick tube at idle.  Likely culprit is the rings/bore not right? 

[My427stang]

I think I'd rather wait to decide until we can see the movie, but if there is pressure pushing it out, then the rings arent sealing, bore/rings/assembly issue, could be a number of things.

Have you changed the oil since the build?  If it runs decent, maybe an oil change and a good run to load the motor would burn anything off

What's the history of the build, any issues like getting very hot early on or any assembly problems?

[Barry_R]

Should not be too much coming out of the breathers after break in - but there will be some.  Not many engines are 100% sealed up.  Probably close to none.  If you want to reduce the airflow through the PCV just insert a slug of aluminum in the vacuum line with a .060 or so restriction hole drilled through it.

[lovehamr]

Dano, don't know if it'll help or not but this is what I did for my PCV.  When I first got mine running using the in manifold position for the PCV (little basket of steel wool and all) valve I would get a good bit of oil in the intake.  So I went looking for a way to get good crankcase evac without a vacuum pump and without dumping oil into my intake.  The answer for me has been an air/oil separator from Moroso.  Since using this setup I haven't had any oil in the intake (or on the valve covers) and I only get about an oz of oil out of the drain after a hard day at the track or a few weeks of street driving.  This is how I did it.

[drdano]

That is a great idea using an oil separator, which would keep the returning air in the intake clean of oil mist = less detonation.  Who's PCV valve are you using underneath the separator can?  I've got a Fram FV181 coming from RockAuto (couldn't find one locally), should be here wednesday and I can try it out.  Rummaging around in my binds of FE spares, I did locate my original '62 Galaxie Z-code metal PCV valve, which may be of some help.  You can pull it apart and clean it, but even better, the internal spring looks fairly common.  I could probably find a lighter spring at the hardware store or online and be able to match it to the idle vacuum. The bypass hole looks to be around 1/8" in diameter.

Doing some reading last night, I think my initial timing may be causing some of the PCV fumes as more timing = more fumes from what I read.  That's one of the reasons from the factory the timing is set so low, like around 6.  I'm currently at 18 initial to try to get a better vacuum signal for carb tuning.  With on-start timing retard of the Duraspark my starter isn't getting killed to bad yet, but when I shut the motor down I get a slight kick backwards on it's last 1/8 of a turn before it comes fully to a stop, so maybe I'm a tad to advanced.

[afret]

Pretty simple to hook up a crankcase evac system and they are pretty cheap.  Just need to weld a tube on each exhaust pipe or header collector.  The location doesn't seem to be critical.



Then run a 5/8" hose from the check valve on the welded tube to the breather on each valve cover.  Works at WOT unlike a PCV valve that would be closed.  Works fine even at idle with straight though mufflers.

[drdano]

What are you using to allow fresh air into the system?  My exhaust is 2.5" to 3" xpipe to 2.5x24" open steel pack mufflers, so pretty free flowing.  If I put the evac connections downstream of my O2 sensor bung, would I have to worry about any oil traveling upstream to it via reversion?