So, the stock PCV valve in my '66 Dart looks like it's staying open under boost, judging by how much vapor gets vented out the breather cap when I was doing some tuning work. Are there any easy to find options for either an inline PCV or check valve - preferably one that fits into 3/8" ID hose?
Back when I had the 2.0, the conventional wisdom was to use the metal-bodied Supra PCV valve because it was supposed to seal up pretty well and act as a check valve.
Is the pcv not closing, or are you creating enough blowby that it has to vent elsewhere? With boost, you are going to create crankcase pressure that can't go through the pcv, so it has nowhere to go, other than out a breather, a seal, or a gasket.
wae said:Back when I had the 2.0, the conventional wisdom was to use the metal-bodied Supra PCV valve because it was supposed to seal up pretty well and act as a check valve.
Metal bodied supra valve has worked great for me on a turbo BP, running over 20 PSI for over a decade.
Thanks to everyone who's responded so far. To answer the questions:
1. I can see the breather when dynoing the car - the amount of vapor coming out looks like it's probably too much to be just blow-by. The engine does have a completely open breather for the "other side" of the PCV - there wasn't much emissions control around in 1966.
2. A lot of the Mitsubishi check valves look pretty cool. Is the barbed end or the threaded end the one that goes to the crankcase? And what size hose does it take?
3. I've struck out looking for the metal bodied Supra valve - these may be NLA.
4. That eBay valve looks about what I had in mind - wish I could get these locally instead of waiting for it to arrive from China.
if you are using plumbing similar to what is modern- as in there's fresh air supplied into the block and then the PCV valve going out of the block- we use check valves all over the system, so that it can still bleed off under boost.
See if you can lift the entire PCV system off of a modern turbo.
There's an absolutely amazing amount of wind that can come out of the breather on a PCV system.
If you have a 300hp engine at 1% leakdown (may be low for an old noodle-bore block like a Slant Six), that is basically the exhaust of a lawnmower engine at full throttle.
If you only need a 3/8" hose for a breather you need to turn the boost up. Then you can use a 1" hose into a gatorade bottle like a real tuner.
MadScientistMatt said:A lot of the Mitsubishi check valves look pretty cool. Is the barbed end or the threaded end the one that goes to the crankcase? And what size hose does it take?
I think it's 5/16". I have a few others that might be 3/8" I seem to recall Toyota having a similar threaded PCV valve. The barbed end is on the pressure/intake side
The pic I linked to (in the middle of the page) is essentially a modern turbo car PCV system added externally to replace the faulty OEM PCV setup.
Go to a hose and hydraulics/pneumatics shop or look in a Mcmaster Carr catalog, I'm sure you'll find a suitable check valve
This is how the Chrysler 2.2 Turbo engines were plumbed.
You can see the PCV valve is located in a T with a check valve on the vacuum line and boost pressure applied to one side of the PCV. It has worked pretty well and the PCV valve is a pretty common one available at nearly any FLAPS.
We would build replacements for the rubber T fittings out of 3/8 or 1/2" copper fittings from the local Home Depot that we soldered together and connected to the valve cover, PCV, etc with short pieces of rubber hose. We'd use a T with a 45 degree soldered to each side. The bottom leg of the T connected to the Valve cover outlet. The top of the T would be mounted at 45 degrees with a bend at the now top to hold the PCV valve (which nestled nicely into the bend and just needed a short piece of hose and some thin clamps to hold it in place). The lower portion of the T would get another 45 to point the hose towards the airbox.
Depending on how things work in your particular engine bay, you may just need a 90 degree bend, a T, a PCV, some chunks of rubber hose and solder.
Hope this helps.
In reply to MadScientistMatt :
PCV Valve - Toyota (12204-46020)
I went through like 6 different PCV options on my turbo Miata, including the metal one that was made for the turbo 323GTX. Long story short, every one of them leaked boost into the crankcase. You can either tune around it or eliminate the problem at the source.
Method #1- put a check valve inline with the PCV valve. Can be had cheaply off of Amazon. This one was made for fuel lines but should work just fine.
Method #2- remove the PCV entirely, cap the intake manifold, and run both breathers to a catch can. If you're running a speed-density ECU you can vent the catch can back into the intake. Many people (myself included) just stuff the catch can with copper kitchen scrubbers and vent the catch can to atmosphere. If implemented well, a small amount of the crankcase vapors make it past the catch can.
Knurled. said:There's an absolutely amazing amount of wind that can come out of the breather on a PCV system.
If you have a 300hp engine at 1% leakdown (may be low for an old noodle-bore block like a Slant Six), that is basically the exhaust of a lawnmower engine at full throttle.
Hmmm... maybe it is blow by after all. I decided to see if I could blow into the PCV valve with a hose and it seemed to shut off OK if I tried that.
Both 300 HP and 1% leakdown might be optimistic here. A fresh slant six would have some pretty good wall thickness, more than a modern block, but there's easily enough cylinder ridge on this motor to catch a fingernail.
I'll have to get a vide of the smoke machine act it's doing under full throttle.
Also - the 3/8" hose is for the PCV valve; the breather side has a filter but no hose.
Even a tight motor will blow a lot of oil mist out the valve cover under boost. That's why you need to run a hose with separate check between the filter and the TB/carb, or through a catch can
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