When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hey folks. Need your advice. I recently bought a 1978 25 Anniversary and I replaced the air filter. Now I'm trying to figure out what to do with the PCV vent hole in the valve cover that used to vent into the old air cleaner. And for now I'd like to keep these valve covers. Thanks.
You can just install a PCV valve in that location and hose it to the manifold vacuum port on the bottom front of the carb. Or you could just install a push in breather cap but it may cause a mess if your valve cover doesn't have a baffle in it. Look in the hole, if you can see all the way to the internal surface of the head then the valve cover doesn't have a baffle. Not sure how the '78's were plumbed but on my '71 there is a line that comes from the charcoal canister to the PVC valve and then routes to the carb. I'll post a picture soon.
Edit - My bad, I'm looking at the passenger side. The PCV valve is on the drivers valve cover, at least on my '71. The port you are referring to as you stated is just a breather tube from the VC to the bottom of the air cleaner housing. Again, you can just install a push in breather if desired or get the proper parts if missing and vent it back into the air cleaner.
Pretty sure that is the suck side, and if pcv working ok a breather should be ok.
have you considered putting the oem cold air air cleaner back on? It was designed for more power instead of hot air off engine.
if you like the chrome that’s cool..
those old valve covers clean up and repaint good too..
dont toss oem , you may sell here for those looking 👀 $$
Did your original air cleaner have one (L48) or two (L82) inlet hoses?
If two, you should put it back on, or sell it on this Forum.
Even though I used the dual-snorkel CAI air cleaner assembly on both cars, I blocked off the clean air tube on both, and used breathers on one valve cover, and working PCV on the other. The stock system pulled clean air for a reason. Make sure whatever breather you use has a filter, as you'll be sucking (clean) air ithrough your engine at idle and part throttle.
Having gone from an open element cleaner on my car to a CAI because the original system was missing from my car I can say the CAI made a noticeable improvement. also I found out the hard way pcv systems are kind of important since mine wasnt functioning and even though I had the breather in the opposite valve cover the pressure that built up caused my seal to blow out on my fuel pump and spray hot oil all over the passengers side of my car after a high rpm run.
Cold Air Intakes MAKE horsepower. The cooler the air the better. I could not enjoy the L88 Compression without the built in Cold Air Intake keeping the combustion air nice and cool deterring detonation. That is the one good thing NITROUS does for an engine, it cools down the combustion air and boosts power.
Cooler Fuel Makes Horsepower. The cooler the fuel the denser it is as well. I have DEI Insulation over my fuel line from the fuel tank to the throttle body. There is a Fire Sleeve over the front 10 front the throttle body. The line goes down the frame and up and over the Bell Housing allowing it to come into the rear inlet on the Holley EFI. No fuel hoses behind the radiator pre-heating the gasoline and metal lines transferring the heat.
My L88 lower carburetor base-plate has provisions for the PCV so I have one hidden underneath. I have a Vent on each side of the baffled valve covers. My engine has very little blow-by and it doesn't spit anything out inside or near my air intake.
Thanks to all for your responses. I think I've learned a lot. Mine is the L-82 and it had the double snorkel intake which was missing the intake hoses. I thought it looked ugly so I replaced it with an open element filter (with a cool 350/Chevy flags decal). But now I get the cold air intake gets me more horsepower. And, the open element filter doesn't give me a place to plug in the PCV vent tube. So I guess I have a decision to make.
Those hoses are reproduced. It doesn't matter at all what your engine looks like when the hood is closed, as long as it works well.
I converted mine from Edelbrock garbage, back to stock-ish, before yanking for an LS swap. Appearance was never a concern. Somewhere I have some plots that I made that show the benefit of the dual snorkel CAI, at least for stock-ish cars. I don't know what the upper bound is, but someone could do that experiment by measuring the pressure drop at the carb intake.
There are a few other ways to do it, too. @pauldana sells a really nice that looks better than anything else under your hood.
But, I'm hopeful the dual-snorkel will fit with the LS engine, too. It fits on the 4-barrel throttle body.
And now I've seen a picture of what the ducting/hoses for the cold air intake looks like. That whole thing was missing when I bought this corvette. I'll bet an after market one isn't cheap. Cold air intake image
For now I think I'd like to find a breather. I already bought one off ebay that said it would fit and it was way to big. What are those breathers called or where do you recommend I shop for one. Thanks.
Here is the setup on my '71. Stock Dual Snorkel air cleaner
Passenger side Passenger side
Drivers side. Hoses come from the charcoal canister in the fender (Evap emission system sucks fuel fumes from the tank through the charcoal canister and into the intake through carb vacuum ports) and one line is "T"ed to the PCV valve and ends up at the base of the carb.
I posted this a while ago. I'm not a fan of chrome, but I ended up finding a chrome breather that fit. Perhaps at Jegs, Summit, or Amazon, some of them specify the base diameter that fits in the grommet. There are several different sizes, and L82 may be different than L48, but you can also order new grommets for your valve covers. Part of the "restore" included the road-tested L48 valve covers.
Originally Posted by Bikespace
Before and after in my 79. Don't mind the thermocouple wires, the experiment they supported proved to me that the L82 CAI system is worth it. I just need to dechrome a bit now.
I recommend Summit Racing. Chrome, black, red, blue, orange breathers, you name it.
The grommet in the valve cover should be a 1 & 1/4 diameter. Find a breather or PCV valve to match it.
I never could understand why the auto industry though it was a good idea to introduce oily mist (blowby) into the top of the carb. That was one of the earliest forms of smog devices, to burn off gases & oils through the carb via a PCV / air cleaner system. I guess the engineers figured that little sponge inside air cleaner lid would soak-up all the oil. Why spray oil down the carb?
Not doing that carb any favors.
So much better to burn off crankcase gases BELOW the carb, via a vacuum port on the Intake. Usually, the #8 Intake port was chosen to accept blowby with a fitting at that location.
In the spirit of, "There's more than one way to skin a cat".
I thought I'd post up my solution. 77 Vette. Lost the factory ugly airfilter years ago. Drivers side, GM Performance PCV routed to base of throttle body. Factory breather tube covered with sleeving to match other lines on engine, routed to bottom of aftermarket airfilter base. A view of the inside of the airfilter, yup a bit home made. But functional installation of a steel nipple to connect breather line. To those who say sucking oil into the carb is a bad thing. See any oil here? Haven't had this cover off in months. No I didn't clean a thing.
Now I realise that I could put in a breather cap that would likely spit oil on my valve cover. And some may prefer that. I prefer this. The air is filtered as the fitting is inside the main filter.
As per cold air makes more power. This is true. But many tests have been done by many different people.
Bottom line is, at the RPM's we generally run on the street, with a mild build 350. The difference is actually very slight. I get rid of excess under hood heat with a vented high rise hood. Which may help. Mostly. This system just looks so much better than the stock setup. So if Iost 3-5 HP at 5,500 RPM. So be it.
Last edited by 4-vettes; Jun 15, 2024 at 10:42 PM.
PCV valve cover vent hole
