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Discussion Starter · #1 ·
I have a quick and probably simple question. I have a built SBC 350. My plugs seem a little fouled, and I see a little oil seeping out of the breather holes in the valve covers. Not much, but a drop or two. Currently, my vacuum/PCV is on the passenger side, and just a filter-breather on the driver side. Is this the correct set up? Does only one of the valve cover breathers hook up to the vacuum? Does it matter which one is hooked up? How often should I replace the PCV valve? Thanks. John
 

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As far as I know the pvc valve usually goes only on one side and the basic breather on the other. The valve usually is on the passenger side of the engine.

How often should you replace the pvc valve, I like to replace mine every other oil change, and especially if it seems to be getting oil blow by.

Or you can just pull the pcv valve out and shake it to make sure it is not clogged up, if it rattles back and forth good, it should be ok.

Otis:)
 

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I like the PVC on one side and one breather on the other that way you get a cross vacume threw the motor. Make sure you have a baffle under the valve cover so you don't get raw oil splashing up from rockers. Not much to go wrong with the PVC valve, like tri5 says just make sure it rattles. Somtimes I will clean it with Brake clean or electrical spray to keep it from gumming up. If your plugs are fowling is it gas or oil? If it's gas select a diff. heat range or re-jet carb if it's oil re-ring or valve guids, or maybe a bad intake gasket sucking oil from valley. Low dist. coil, coil wire, plug wires, voltage? Lon
 

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Discussion Starter · #4 ·
Thanks guys. That was the confirmation I needed. Next, I'm going to check the gap on the plugs. I don't think it is oil on the plugs, but wanted to check this oil breather issue before I replace the plugs. John
 

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i dont run a pcv valve they are not necessary. all they do is cause plug fouling form pulling dirty oily air into the carb. i run a open k&n breather and thats all.
 

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Yep, you can get away with not running it but my experaince has been that they do keep your motor cleaner, not as much sludge build up. The old Chevy with just the breather down the back side of the block would build up sludge after 60-70k'z. On a street/race motor it's not as important. We used to run breathers with 3/8th" lines going to our headers to evacuate the system under power on a S/B Chevy powered '48 Anglia. Lon
 

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If the PCV is causing plug fouling then you need an overhaul or you may be missing the splash shield around the PCV in the valve cover. One of the main purposes of the PCV is to keep from having all the oil fumes and drips under the car. California gets highly offended about oil drips.
Dave
 

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Discussion Starter · #8 · (Edited)
OK. So the last couple posts suggest that I don't need the PCV. Is it better to have it or not? My engine tends to run at higher RPMs, unless I'm just cruising around town. I have a turbo 400 tranny, and a posi rear end with 4.56 gears. So, unless I"m going under 35, the engine starts to wind up. My engine has been bored .60 over torque plate, and has a 750 CFM Edelbrock 4 barrel. The engine has a comp cam 12-250-3. Unfortunately, I don't know exactly what that means, and if it is considered aggressive or not. So, do I have the type of set up that would benefit from a PCV valve, or not. What do the experts (you guys) think? I appreciate the help!!! John
 

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OK. So the last couple posts suggest that I don't need the PCV. Is it better to have it or not? My engine tends to run at higher RPMs, unless I'm just cruising around town. I have a turbo 400 tranny, and a posi rear end with 4.56 gears. So, unless I"m going under 35, the engine starts to wind up. My engine has been bored .60 over torque plate, and has a 750 CFM Edelbrock 4 barrel. The engine has a comp cam 12-25-3. Unfortunately, I don't know exactly what that means, and if it is considered aggressive or not. So, do I have the type of set up that would benefit from a PCV valve, or not. What do the experts (you guys) think? I appreciate the help!!! John
i would get rid of the breather and the edelbrock carb.
 

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I went to Comp Cams website to look up your cam specs.
110 lobe separation
106 intake center line
284 intake duration/ 296 exhaust duration
.507 intake lift/ .510 exhaust lift
They recommend a 2800+ stall, headers, and gears.

I would run a breather in each valve cover. A pcv valve is held nearly closed at idle during high manifold vacuum. When the throttle is opened, vacuum drops. The valve now opens, letting air to flow through the crankcase. The air ventilates the crankcase of blow-by gasses and carries them to the intake manifold to be burned again. The question I would have is, does the engine produce enough vacuum for a pcv valve to function properly? (with that cam) If you do decide on a pcv, get rid of the breather.
 

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If you run a PVC you have to run at least one breather, if not it's like sucking on a straw with your fingure plugging the other end. If you do not run a PVC or breather you will probably blow out gaskets and worse the rear main seal. If you do not have enough vacume for the PVC to work I doubt the carb would idle very good. I would do like Walt says, take a manifold vacume reading. JMO
 

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If you run a PVC you have to run at least one breather, if not it's like sucking on a straw with your fingure plugging the other end. If you do not run a PVC or breather you will probably blow out gaskets and worse the rear main seal. If you do not have enough vacume for the PVC to work I doubt the carb would idle very good. I would do like Walt says, take a manifold vacume reading. JMO
You're right. I don't know what I was thinking about (must had been a brain cramp). You do need a breather for a pcv valve.
 

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My opinion is you don't need a pcv system. Non of these cars had 'em to begin with.

I bought a new Dodge 383 back in 1964. That was the first year of the pcv valves being required in California. What Dodge did was cram a rubber plug into the downdraft tube, run a hose from the valve cover breather into the air cleaner and connect the pcv hose to engine vacuum.

I went to the dealer and bought all the correct parts for a 1963 Dodge and put those on. Immediate improvement in the way it ran.

Earlier cars that had to have retrofit pcv valves ran like horse manure including the tri-fives. Dual quad cars and FI didn't require the retrofit I don't think. The way the cars ran is what turned me off to pcv.

To each his own. I vote no on pcv valves. My engine ('67) had pcv originally but not now and it runs pretty good.
 

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Discussion Starter · #14 ·
Thanks for the great input, and spirited debate. One of you asked how much vacuum the engine developed, and the short answer is, not much. I have my valve cover off now so I can't test it, but I recall it was about 9" at the manifold. I tested it when I put in power brakes, and I am running a dual 8" booster plus a reserve can. Even that barely does the job. My engine appears to be a mid seventies era ('76 is my guess) 350 that probably had a PCV valve originally. When they bored and rebuilt it with the new cam, they put a PCV valve back on. I'm tempted to try running the car with just two breathers, no PCV hook up. I did notice some fouling of the plugs, so if the PCV may be causing that, I can't imagine that's very good for performance. As it is, I only get about 6 mpg. I definately do not want to have a problem with my gaskets blowing out, and don't want pressure building up. Does anyone see a risk involved with replacing the PCV with a breather, so I would just have a breather in each valve cover? Thanks again. John
 

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No.
You must vent the crankcase. The early engines before pcv had downdraft or road draft tubes that were cut on an angle and actually drew air out of the crankcase while driving.
SBC engines had a hole in the rear of the block up to at least 1967 for the downdraft tube. Don't know if you have that or not.
If your block doesn't, I would at least place oil baffle type breathers on the oil pan.
 

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With only 9 lbs vacume at idle your carb is running rich at idle unlesss you have re-jetted,etc. for that problem. Are your plugs oil or gas fouled? You seem to have to big of cam for the street and especially for an automatic with out a tall stall. Nothin wrong with the rear gears! Sounds like the motor is built for high RPM's, you would get better throttle responts, better gas milage and more torque for the street with a smaller better cam and maybe a smaller carb. Better braking would also be a plus. Again are your plugs fouled by gas or oil? Black plugs are to rich, oily is oil. Black smoke out the exhaust is gas, blue is oil. Lon
 

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Discussion Starter · #17 ·
I think many of you are honing in on my problem. I think that the person who "built" the drivetrain for this car, built it to run the quarter mile. I have tried to tame it for the street. When I bought the car, it had huge headers, with 4" collectors, that dumped into two cans that were hardly mufflers. The tranny also had a 3800 stall converter, that I have switched to a 2800. I need to pull the plugs again, but I seem to recall they were somewhat black, and maybe a little oily. Again, I'm going by memory, and need to pull them to look. It wasn't real bad, just looked a bit "wet" to my untrained eye. Other than the issues Im describing, the engine appears to be in great condition, and runs strong, especially at higher rpm. THe idle is a bit rough, at least until the engine gets to 180 degrees. Does this help the debate? If there was a hole in the back of the engine, I doubt it is there now. I do not believe there is a tube back there. I have no smoke of any type out the exhaust. Just some water.JOhn
 

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We run an 11 sec GTO and a 8 sec Firebird. While these are pure Pontiac engines, the science is the same. BOTH have a pcv and a breather setup. At the track or on the street, we had MAJOR oil blowby (and leaks!!!)due to too high of crankcase pressure without this setup. We were running Moroso's evac closed system which was meant to scavage the crankcase pressure. Yea right....On the street AND at the track, our engines had oil leaks all over the place. Please take this as more than an internet forum grain of salt. Run a pcv valve in the pass side hooked up properly to full time vacuum port, and run a breather on the driver's side. Now you can begin to narrow down your problem if this doesn't resolve it altogether. Best of luck,,,, Rich
 

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Discussion Starter · #19 ·
Again, thanks for all the great advice. I think I'm going to keep things the way they are, a PCV on the passenger side, and a breather on the driver side. That's the way I got it, and it works, so I'll check my plusgs and see if my carb is rich. Also, I Hate leaks, and don't want to pressurize my system. I noticed last night that with the engine idling, I could pull the PCV valve from the valve cover, and the valve remained open at idle, sucking air. The engine ran fine that way. When I put my finger on the valve to block it, the engine staggered to the point that it was going to stall. So, for whatever reason, that setup seems to be the way I need to go. Unfortunately, I have aftermarket aluminum valve covers, that do not have any baffles oneither side. However, I didn't feel any oil on the PCV valve, and it doesn't seem to spray up there, so hopefully, I"m not sucking oil. Oh well, what will I find to F$%# with next? JOhn
 
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