I have an Edelbrock 4x2. Very small transfer tubes between carbs, not sure if it could be adapted to pcv I’m thinking wherever you drill for vacuum it will mostly affect one carb. Is it worth the hassle and headache or should I just leave it alone and run road draft?
Appropo of nothing, thought I'd point out this is exactly the kind of thing we used to see in say, Pop. Mechanics or the other Late Lamented Print Magazines being discussed in another thread. It used to be cool to save money..
I just went to Summit to look it up, believe it is an AC Delco part, I recall the box. With a 90 degree fitting. Best match I have is P/N 6487779.
I used to do arbritation for Chrysler , customer would complain of no brakes ......hed to have the crrect pcv for x amounts of panic stops. Wrong calibration and the engine didnt have enough vac for a panic stop.........customer would install a new valve from K mart and engine would idle terrible and the power brakes wouldnt work right ???
I assume this is what Bobss396 is referring to; ACDelco GM original equipment PCV valves are an emission control component. These valves are a GM recommended replacement for your vehicle's original part. The PCV (positive crankcase ventilation) valve controls the volume of crankcase vapors that are drawn into the intake manifold. A restrictive PCV valve can cause oil leaks or increase oil consumption. These GM original equipment PCV valves have been manufactured to provide you with the same performance, durability, and service life you expect from General Motors. I am guessing the underlined bold section above is the key to having the right working PCV valve.
Can choosing the right PCV valve help improve the brake pedal performance of those rather small diameter brake boosters sold all over the place. It has been my experience that they never seem to work right offering a very hard pedal.
Think of it this way. When cars used to use a draft tube for Crank Case Ventilation they only worked when the vehicle was going down the road. @idle your vacuum is low because or your camshaft (probably) but it comes up when you are cruising. basically going down the road. So while your manifold vacuum is low at idle it should still be high enough to make your PCV work when you are cruising. Same as the old days
The adjustable Wangner PCV, does it come with directions on finding the "sweet spot"? Can you post those directions? Would be good to know for the DIY adjustable modifiers.................................. Found some info on the net, https://www.hotrod.com/articles/tunable-pcv-valve-fixes-cruise-woes-engine-leaks/ If you look at the makings of the Wagner you can see why it's pricey!
Having breathers and having a PCV are mutually exclusive. They are polar opposites. (The same with road draft tubes.) PCV valves came about in the early days of pollution control when the Feds mandated that the crankcase oil vapors had to be burned in the engine and not vented to atmosphere. So breathers were eliminated and sealed crankcases with PCVs were the new regs, thus no evil vapor dumping. If you have breathers and you add a PCV you're just adding a vac leak and controlling (trying to) it with a variable valve but for no reason and for no anti-pollution benefit. The only thing you're getting is more tunning issues. I like this illustration of how a PCV valve works. The color helps me note the plunger position with less fog in my pea brain. It shows how the intake vacuum is the signal that varies the position of the plunger in the valve which controls the flow. I don't mean to come on like an expert. I'm not. I just had to get a good working grip on the subject back about 15 years ago when I was messing around with turbocharged, Mopar 4-bangers, cranking the boost up, doubling the horsepower and quadrupling the crankcase blowby.
Taking into consideration info pic above modifying a stock PCV with a set bolt/screw only changes the plunger seat at idle, after that the excising spring rate operates as stock. You have only modified the operation at idle.....................................
The first uses of PCV syswtems were "Open", the were used with a breather that allowed air into the engine which is drawn through the engine and out the pcv system. Under conditions, like idling or during hard acceleration, the pressure inside the crankcase can exceed what the pcv system can exhaust and excess pressure is vented out the breather. This prevents blown seals, but it allows hydrocarbons into the atmosphere. This lead to the "Closed" system, where the breather side of the system was closed off and routed instead to the air cleaner housing. With this system, when crankcase pressure exceeds what the pcv system can evacuate excess pressure is vented into the air cleaner assembly and is then drawn into the intake system and into the combustion chamber. This prevents the hydrocarbons being released into the atmosphere. It also provides a source of cleaned air for the intake of the pcv system, so it provides 2 benefits. But back to the main point why I posted this, pcv systems were indeed used with breathers, that was the original design. That is correct, the screw in the top will only help you dial in the correct amount of pcv action during idle conditions. If the pcv valve is not capable of evacuating the crankcase pressures under cruise or acceleration, than it requires a larger body with additional flow capacity. It would be had to make that adjustable. You could start with the largest valve available and somehow modify it to close off part of the orifice I suppose.
I use the screw adjustment pcv modification on a sealed crankcase 355sbc around 500hp, no breathers at all. I also have a data logger on board that monitors crankcase vacuum. At idle, the pcv pulls 8-10"Hg in the crankcase. 2500rpm 55mph 4th gear cruise it pulls about 15"Hg. Here's a graph of crankcase pressure during a 3rd gear WOT pull from 2500-6200rpm. Red line engine rpm. Yellow line crankcase vacuum. Blue line WOT switch. Crankcase vac starts out at 12.6"Hg. By the time the engine reaches 6200 at the end of the 6.64second long WOT pull, crankcase still holds 4"Hg of vacuum. The PCV valve is installed in the top of a homemade separator tank that's made out of glued together pieces of pvc pipe... There's a large dia standpipe that comes up inside the tank from the bottom, it's attached to a large check valve to act as a safety vent in case for some reason the crankcase ever sees positive pressure. There's also a small drain port for the outer chamber, most I've ever gotten out of it was about a teaspoon. I might check it about once a month during the summer. No baffles inside the valve covers, large dia upward angled fittings/hoses keep air velocity to a minimum which helps prevent pulling oil into the pcv system. The car also has a nitrous system and an electric vacuum pump, neither were activated for the above test pull. Grant
That is some very interesting information. I'm still not done absorbing it, but I'm thinking that a graph with pcv vacuum plotted against crankcase vacuum could prove informative.
I use the screw adjustment pcv modification on a sealed crankcase 355sbc around 500hp, no breathers at all. I also have a data logger on board that monitors crankcase vacuum. At idle, the pcv pulls 8-10"Hg in the crankcase. 2500rpm 55mph 4th gear cruise it pulls about 15"Hg. Just to bring up some points that people may not know..There is a max vacuum that the crankcase can be with out causing issues? I think I read about 12" tops as any more [for sustained period] will cause the wrist pins to run dry? Engine crank seals will leak a lot of air, but don't know how much vacuum the seals can tolerate in stock direction before they have to be put in backwards..
Without an inlet it's not evacuating the crankcase, removing moisture that builds due to condensation, leading to shortened oil life and lacquer/varnish deposits.
Yes but for race engines its helping ring seal and lowers windage so is a hp gain; oil gets changed frequently so acids not a concern..Street wise a controlled vac/air in could be a win/win. I think new cars, especially with turbos [boost of some sort] have some sort of PCV vac/air flow system..They should for all the hoses and stuff on the engines!
I thank you for the history lesson. I pretty much ignored PCVs when they first appeared and put breathers in what I owned, because "racecar", at least on the weekends they were. That the Feds and Detroit would cook up a halfass, part-time PCV doesn't surprise me. But in my defense, I said "early days" not "earliest days". So if you're right, maybe I'm sort of right??
Most aftermarket air cleaners have a fitting for a hose to one valve cover, and you can put the PCV in the other. I have always just used a breather in 1 cover and a pcv in the other so I appreciate learning why it would mabe a little better to vent to the air cleaner.
For street use, at least, a PCV system needs filtered air inlake and ideally (with a V engine) it should be on the opposite side from the PCV valve ie: left front intake and right rear pcv, so that air is drawn down thru the pan and up the other side. I heard, from a reputable source, a test of correct PCV's calibration is to pinch off the hose leading to the carb. At idle and you should look for RPM drop of 50-70. More drop you need a smaller valve; less drop and you need bigger. A digital tach is helpful.
Shoot, I turn the AC on and the engine will stall! I understand if you pinch the pcv line the engine rpm will drop from less air seen in the intake track but because of less air the fuel mix becomes rich; a double down.
My main seals are reversed, cast valve covers, no dipstick. No problems at all with 15"Hg. I think some of that poor oiling misconception might come from the illusion of oil pressure "loss" that comes along with crankcase vacuum. At 15"Hg my oil pressure gauge reads about 8psi less than it would if the crankcase had no vacuum at all. That is due to the fact that the oil pressure gauge is comparing oil pressure against atmospheric pressure instead of crankcase pressure. In reality, the oil pump still creates the same pressure gain with or without crankcase vacuum. There is also no condensation to be found inside the engine when I run the valves, probably because the boiling point of water drops quite a bit as vacuum increases. The engine has ZERO oil leaks with my pcv setup, but my Toploader 4spd always seems to have a drip hanging from the bottom of it's case. Thinking about adding a little pcv port to the Toploader just to see what happens Grant
I have always believed the valve part of the PCV is to stop a flame traveling to the crank case in the event of a blow back in the intake and that the metering for the system is what the fitting or tube size on the carb is. The length of the hoses in the PCV system also would count as the longer they are the more resistance there will be. JW
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