Have a dual-four setup with a breather on the p***enger-side valve cover and a PCV on the driver side going into the front carb. Since the PCV is flowing air into the carb, will removing the PCV (and capping that vacuum port and just putting a breather on that valve cover) affect idle or on-throttle and necessitate the carb(s) needing adjustment? Please no lectures on the need of the PCV. I get it. I'm wanting to take it off as I know it's pulling more oil through than it should so for the interim, I'd like to stop that.
The place where the PCV goes in to the engine needs a baffle. Nothing space age, just a couple layers of a 3 M pad will do. Also, make sure where it goes in to the carb is the correct port. A PCV will not affect idle if it works right. Keep tinkering, never give up!
What type of 3M pad. 3M makes so much stuff. The valve covers have baffles but I'm not convinced they are doing the job. The inside of the valve is covered in oil. Hold it up and it drips back out. It's running into the front-center 3/8 vac*** port on the front of the carb.
You're going to get a little oil buildup in the PCV valve, simply because it's pulling crankcase vapor, which consists mostly of oil and residual moisture. If you were pulling enough oil to be a problem, you'd be smoking from the tailpipe. Pull the other end of your PCV hose and see how much oil buildup there is there, I'd bet it's not much.
You may have to tweek the carb a bit when you remove the pcv, anytime you change something intake related it takes a little tunning and tweeking. You should not have to rejet if that is what you are asking. Which carb is you priomary carb and which is your secondary carb? You should run your PVC valve to your primary carb. If it is not blowing bloue smoke it is not ****ing oil into the intake.
I had to adjust my idle mixture screws when I added a PCV valve to my Chevy engine that did not have one. You are going the opposite way but you may need to re-adjust the idling. Baffles are the cure for ****ing oil.
Hmmmm, the rear carb is the primary carb. PCV is going into the front carb. I'm burning about 1qt per 150 miles, am fouling plugs like no tomorrow and am getting virtually no smoke out the exhaust. Yes, that's right - no smoke. And there are NO leaks. I believe the PCV may be at least partially to blame, so wanted to unhook it for a while and see how things go.
I built a short block for a fella a few years back and he was buring oil like no tomorrow. He fiddled with the PCV aquiesed me of having built him a bad lower end, wich could have been tru **** happens, and one of everything else. We pulled the heads and started checkind. His 55 year old heads not only needed the valves ground but also needed guides. He didn't believe that could be the problem so I loaned him a good set of heads off myshelf. Cured the problem and he had something to drive while he was getting his heads redone (I refused to redo them for him). Anyway long story short heads wear out.
It's not the PCV then. If that much oil was p***ing through your PCV, it's going right into the cylinders and you'd be smoking badly from the tailpipe, since it would be getting mixed with your air/fuel charge. Like ****** said, it's probably bad valve guides or seals. Could be shot piston rings as well. You said virtually no smoke, so are you getting some? When does it smoke? But try disconnecting it and see if there's any improvement in oil loss. I'm betting not.
If there's any smoke it's at start up (i know - valves) but again, it's a pretty minor insignificant seeming amount and not consistent. SBC. Lower half was completely rebuilt. Upper half has new aluminum heads (i dont know what kind). Lower and upper were done by different people (not me).
1 quart every 150 miles is huge. Considering it's fouling plugs left and right, the oil probably isn't getting burned off, and is just coking everything up. I don't think even an unbaffled PCV could pull that much oil that quickly, considering you're only getting oil splashed around under the valve covers. I'm wondering what the insides of your cylinders look like. It the plugs are coated, I'd bet the valves and chambers are as well. You're sure there's no external oil leaks? Because it's not spotting your floor up doesn't mean it's not leaking under a load, meaning while you're driving. That's a lot of oil. Many people also use the wrong PCV valve. Low idle vacuum motors (like with big cams) need a PCV that works at low vacuum. They have a lighter spring that allows the valve to be opened more easily. Use one of these on a stock engine or one with good vacuum, and it's more or less an open port. Conversely, using a stock PCV valve on a low vacuum motor is causing the valve to not work correctly, if at all. Do you know for sure your PCV valve even works? With the engine running, pop the valve out of the valve cover, and without turning it over, put your finger over the hole in the bottom of the valve. Engine vacuum should **** your finger over the opening pretty firmly if the valve is operating correctly. When rpm goes up, vacuum drops, and the PCV valve closes. So the valve should only function at idle and when cruising, and should shut under heavy load conditions. The only ay to check heavy load operation is on a dyno or with a long length of hose, so you can run the PCV valve into the car and check its operation while driving. See if the valve works correctly first, then at least you'll know if you can rule the PCV out.
This is the first time I ever read/heard anything about the PCV hose needing to go to primary carb. What difference does it make? You are feeding crankcase fumes into the intake either way. My 355 sbc has the Edel. air gap 2X4 setup with Edel. carbs and I bought the whole setup new. Don't remember any mention of this requirement in the very detailed instructions that came with the setup. I hooked up to front (secondary) because things are sorta crowded between front and rear carbs. I'm trying to learn something here, not stir ****, so what is the rationale? Dave
Technically, both carbs should see the same idle vacuum so long as you're running the PCV on the correct vacuum port, so it shouldn't make a difference. When you crack the throttle, the primary carb operates, but the vacuum signal through the secondary carb should also react to the change. My only thought is that the primary carb might react a little quicker to vacuum changes under a load. The only vacuum difference between the two carbs should be timed vacuum (the port above the throttle blades).
Yes it's a lot of oil. I dont think it is leaking under load when driving because it would likely then be splashing something underneath and making a mess but it's always clean underneath and no leaks when letting it run or rev in the driveway. So that in combination with the fouled plugs makes me think it is not leaking. But the lack of smoke has baffled me. I'll test the PCV for proper function tonight, but am going to leave it replaced by a breather for a little while too.
PCV is opening and ****ing strong at idle. I don't know about under load. Here's a pic of the baffle under the valve cover. How does it look to you guys that have seen ones that work and ones that don't?
Looks pretty much like all the others. If you are still worried about it, line it with a little Scotch-Brite, but I don't think you're pulling oil through the PCV.
I believe you are backwards. PCV Closed at idle(hi-vac) , opens(via internal spring) as throddle opens (vac drops)
It's not that simple. A properly functioning PCV valve is open more at idle than while cruising, but flows more when cruising than at idle. http://www.youtube.com/watch?v=c1Jb_sfpZsI http://www.autoshop101.com/forms/h63.pdf
Check your front or rear mains. Can still look pretty clean and be douching oil under load or while driving. Can also drive you nuts. Thats a lot of oil....
My understanding is that the high vacuum at idle opens the PCV and as the vacuum drops the valve starts to close but is still open with lower vacuum keeping it from closing completely.
The valve is made internally to flow less volume at idle when blow by is not a big problem and additional air could upset the idle mixture. When the vacuum drops due to a load on the engine and blowby is a bigger problem then the flow through the valve is increased ****ing out the added blowby. It's an internal design thing. It doesn't shut off the flow unless there is a backfire in the intake to prevent an oil pan explosion when the flow is in the opposite of the desired direction.
Any retrofitted PCV needs to be from a motor with similar cubic inches to get the vacuum signal in the ball park.
Not necessarily true, it needs to be matched to the vacuum level of your particular engine. For instance, the old Z28 302 valves work well on low vacuum engines, regardless of displacement. That's what I run on mine, and I know it works perfectly.
If you block off the PCV valve you will have oil leaks and use much greater than you do now. I would NOT use 3M Scothbright pads for a baffle, it contains an abrasive. Get a crankcase vent filter and adapt the media. ~Alden
I have a few thoughts maybe all wrong. You mentioned the engine is rebuilt, did you use a stock oil pan and dip stick. I ask because there may be to much oil in the engine and churned up and ****ed out by the PVC. If when the oil is low does it stay at that level. Another thought is could you take the hose after the PVC and connect it to a container then a second hose from the container to the intake. This way you can see if the oil is leaving the engine by way of the PVC. Bad valve guides or valve guide seals will cause a puff of smoke on start up then clear up but can consume a lot of oil, I know
It's not like the material in the baffle is breaking up and getting into the engine. I've done this in the past with no issues, but there's also no reason to not do it your way, either.
It's going to an engine shop this weekend. Not discounting anything so I suppose the main seals could be bad, but that would not explain the fouled plugs. It's not a stock pan. It is a 7 Qt Milodon pan. After adding 7 qts after an oil change, the dipstick reads full. It'll keep going down on the dipstick, at least to the 'add 1 qt' mark at the bottom. Haven't let it get lower than that. I think you guys have been right about the PCV - it's baffled correctly or at least to a basic standard and the hose doesn't appear oily. Hopefully it's not more involved than the heads and valves but I'm prepared for whateve and would not be surprised if it's the upper and lower half.
Long follow-up here... So the shop finally pulled the engine apart and found that the oil control rings were worn down to nothing and had also damaged the cylinder walls. So a full rebuild of the block is in order. They thought it looked like a 10-year old build from he stampings on parts like the main bearings. However, one lower bearing appeared to have been replaced as it had a more recent date code. They also stated the pistons appeared to be about the cheapest ones someone could get. On the bright side, the heads pressure checked out A-OK. Cam checked out good too, no wear. Their diagnosis was that the dual fours had, overtime, washed too much fuel down the cylinders and that 10-years is about right for that type of build, meaning the dual fours over-carburate by nature and that over the course of 10-years that's to be expected. They said the carbs could be metered down to the minimum to minimize this and would ideally need to be done using a 4-gas ****yzer to take the guess work out. They don't have one of these and they don't know if anyone is town that does. Ultimately it needs a re-build and is getting bored .040 over (is at .030 now) and all new internals. On the carbs, at least for idle mixture, I had them as absolutely lean as they'll go w/o the car backfiring or stalling out. I've never messed w/the jetting and internals. Up to now I couldn't gauge richness by looking at the plugs because they've always been so darn oil fouled, who knows if they were also gas fouled. I have a couple questions for you guys... 1. I'd been under the impression that former build (.030 over bore) was fairly fresh. At minimum 3,000 miles to maybe twice that. If the guy used dirt cheap pistons, perhaps even recycled/scavenged from another engine, it wouldn't surprise me if he did the same with the main bearings... and possibly was one short and had to get a new one, which would explain the mis-matched date stamps. I also have somewhat hearsay to back up at least the age of the build, as the guy that had it before me (he did nothing with the block but re-did the whole upper half, which is the part that seems OK in all this; he also only had the car a short time so I know he didn't put more miles on it then noted earlier) said that when he replaced the heads, that the cylinders looked really good and he could still see the hone marks from the prior re-build. He's got no reason to lie because a) I didn't buy it from him and b) he didn't mess w/the block. Also, I know that this guy's the one that put the dual fours on. When he got it, it was a tri-carb setup. So whether it's a 10-year old build or three, it hasn't been a dual four engine all that time. But who knows what all combinations it has had. IF it was rebuilt fairly recently, what could wear the rings and cylinders so quickly? 2. My understanding of fuel wash is that it could do the above noted damage pretty quick, so that could be one answer to #1. I'm looking for your thoughts on that and other possibilities. Also, my concern is that if this wasn't a 10-year old build, and fuel wash was to blame, I don't want to spend this much money only to be right back here in the same place in a year or two. 2. Oil control ring wear notwithstanding, is is possible that the worn oil control rings damaged the cylinders BUT that the engine would still have good compression? I'd tested compression and all 8 were between 150 - 155. In other words, if the oil control rings wore down and damaged the cylinder walls, how would the compression rings still be doing such a good job? Note, I don't know how damaged the cylinders are, so take into consideration that it could be minor but enough to the point that once everything is all apart, you wouldn't want to rebuild w/o the whole shebang. 3. I understand that once you over-carb and over-cam and over-everything else an engine it's not going to last like a new car, and I'm OK with ten years. Does this seem right to you guys? But again, my understanding of bad fuel wash is that it could cause this type of failure much quicker rather than over-time. 4. IF fuel wash is the issue or a main issue, I should be able to see gas fouling on the plugs pretty quick once it's no longer burning oil. How much fuel washing is attributable to idle mixture (which I addressed and the shop knows to tune it as lean as possible) and how much is attributable to non-idle (when actually driving the car)? I would think at WOT, for instance, it'd be be more likely to burn it even if a bit (or a lot) rich. I've also alerted them to check the fuel line pressure coming off the pump, as the gauge usually reads 8 - 9 PSI, which is really high, but I question if it's right as I'm not flooding and don't have hot start problems. If you're still reading, thanks for sticking it out and thanks in-advance for your help!
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