buZy Posted January 6, 2006 Share Posted January 6, 2006 Is it Required that I run a PCV valve on my engine for normal street driving? Could I run just a standard breather on each valve cover instead? This particular valve I dont understand. When I remove the hose/valve assembly from the motor and apply suction on the hose end with my mouth (yuk) simulating maximum motor vaccum at idle it just draws unrestricted open air. So to me (being dumb as I am lol) it appears like a big vacuum leak. Is my valve shot? I'm having trouble with my brakes getting vacuum. I don't understand the theroy here at all? Now if the valve closed when I applied suction how could it ever be opened by internal crankcase blow by with a breather on the opposite valve cover. Im sure these valves have purpose but I dont understand them fully. Maybe this is a dumb question. Quote Link to comment Share on other sites More sharing options...
Guest 305240 Posted January 6, 2006 Share Posted January 6, 2006 I think you may be confusing a few things here. First, no, a PCV valve is not needed for an engine to run. For many years a downdraft tube was used. I guess the EPA people got tired of seeing the oil puddles forming under the car...lol. I currently do not run one on my 260Z. I'm running an Arizona Z 4 bbl manifold. I have 2 ports on my intake. One goes to the brake booster, the other to my dizzy. As far as I can understand, this is ArizonaZ's recommendation. Someone please correct me if I'm wrong. All the PCV valve (positive ventalation valve) does is suck oil fumes into the intake manifold. The brake booster is ported off another part of the manifold. Some builders and racers say the PCV system is needed to make sure there isn't too much pressure inside your engine. I've heard just the opposite. All I know is the K&N filters I have on my block and valve cover have never leaked any oil or have any oil residue on them. Luckly, I live in a no smog area. If you live in a smog area, by all means use one. A simple check to see if it's good or not is try blowing thru both ends. If you can, replace it. One of the best people to answer this is Grumpyvette. Take his word as gospel. Quote Link to comment Share on other sites More sharing options...
DavyZ Posted January 6, 2006 Share Posted January 6, 2006 Is it Required that I run a PCV valve on my engine for normal street driving? Could I run just a standard breather on each valve cover instead? PCV = Positive Crankcase Ventilation Nope, you can use a breather on each side or on one side, but many are prone to oil seepage/leakage. I personally don't like the idea of the crankcase venting straight to the atmosphere when it could be recycled and burned in the cylinders instead. To my knowledge you will not gain any horsepower by running breathers. On the 350 I am building up, I went straight to the PCV instead of breathers for the aforementioned reasons. Just my $.02 Davy Quote Link to comment Share on other sites More sharing options...
buZy Posted January 6, 2006 Author Share Posted January 6, 2006 There is no smog inspections in MN anymore. X gov Jesse Ventura (yes the ex hollywood pro-wrestler) put an end to it years ago. Besides the car is a 71 and last time they only went back to 1975 like in Cali I guess. Ok when I blow into the hose side the air flow is stopped 95%. A slight bit still gets through. When I blow into the valve cover side the air flow is passes through unrestricted. What does this mean? I removed the valve itself from the alum housing. It appears to be a cartridge type valve insert. In it's natural free state the check valve looks neither fully closed or open. It's hard to tell exactly upon close visual inspection. When I lightly shake it I hear a rattle noise inside and feel somthing moving inside the cartridge. I'd just run breathers if I could find ones that didn't make an unreasonable mess. Anyone know of a good one? Power is not an issue. Having the motor run right and the power brakes operate properly is. Maybe my power brake problem is something more going on but I figure start with the vacuum basics first. Quote Link to comment Share on other sites More sharing options...
DavyZ Posted January 6, 2006 Share Posted January 6, 2006 Since they are so cheap to replace, when in doubt, replace it. I've never put my mouth on them or tried blowing in them, hmmm. You should hear the thingie inside sliding back and forth freely just as you stated, but leaking past when the valve is closed? Hmmm. Davy Quote Link to comment Share on other sites More sharing options...
johnc Posted January 6, 2006 Share Posted January 6, 2006 You PCV valve is working exactly as designed. In high vacum situations (idle, drop throttle) the valve opens to allow scavanging of the pressure buildup in the crankcase. In low vacum situations is essentially closes. Remember, the whole PCV setup is a closed loop with one part of the loop in the air cleaner drawing in filtered air and the other going to the intake manifold. Its not acting as a big vacum leak. Also, make sure your oil cap is the non-vented type or you will introduce a leak. Quote Link to comment Share on other sites More sharing options...
SpeedRacer Posted January 6, 2006 Share Posted January 6, 2006 A PCV system is actually beneficial for your engine. A lot of combustion by products get past the rings and seals and end up in the crankcase. Harmful vapors can break down and dilute your oil and cause corrosion of engine components. The PCV system helps to keep the crankcase and your oil cleaner for a longer period of time than the old "open" breather systems by drawing a lot of the “bad†stuff back into the intake. This is one reason why the car manufactures have been able to extend the length of time between oil changes. I would highly recommend that you keep the system. Quote Link to comment Share on other sites More sharing options...
deMideon Posted January 6, 2006 Share Posted January 6, 2006 Well could someone help me out with this as well? I currently have open breathers. How would I go about connecting it up? Which way does the pcv need to face? I would assume I need a tube going to both valve covers right? Quote Link to comment Share on other sites More sharing options...
PeterZ Posted January 6, 2006 Share Posted January 6, 2006 The valve flows in the direction of the valve cover to the intake manifold and is shut by manifold vacuum. High vacuum, low blow-by condition (idle) the valve is closed. Low vacuum, high blow-by condition (WOT) an internal spring opens the valve to allow more venting to the intake. The valve will flow easily on only one direction (to the intake). It also serves as an anti-backfire valve so the intake flame doesn't go the wrong direction into the crankcase blowing out all your seals and making interesting shapes out of sheetmetal valve covers. No PCV on the car makes for more frequent oil changes as the nasty exhaust gasses that blow past the rings are not evacuated and your oil gets contaminated faster with poo-poo. The additional hose to the air cleaner is to allow for proper venting should the amount of blow-by exceed the ability of your PCV hose for the conditions. (such as prolonged full throttle runs) Pressure in the crankcase means more oil leaks too. I suggest run the PCV and additional hose. It may clutter the looks but it is one "smog" device that is actually good for your engine. Quote Link to comment Share on other sites More sharing options...
Brad-ManQ45 Posted January 6, 2006 Share Posted January 6, 2006 As others have stated more wordily - PCV=cleaner and longer lasting engine. Quote Link to comment Share on other sites More sharing options...
buZy Posted January 8, 2006 Author Share Posted January 8, 2006 Ok update: Looks like my motor pulls 8 Hg/in of vacuum @ 1000 idle rpm. That is with everything plugged too. Pvc and brake booster are the only accessories I have. Can someone tell me how much vacuum is needed to run just the booster? Or with a pvc and booster? If I had to could I change cams without pulling to motor and doing cam bearings? Or do I have change bearings to change the cam? How often is this done with success?? Quote Link to comment Share on other sites More sharing options...
Brad-ManQ45 Posted January 8, 2006 Share Posted January 8, 2006 What kind of cam are you running to only have 8" of vacuum at idle? Sure your timing isn't off? What shape are your valves/guides in? Inquiring minds want to know... Quote Link to comment Share on other sites More sharing options...
buZy Posted January 8, 2006 Author Share Posted January 8, 2006 The Cam. A Very good question. I dont know? I didn't build the motor. The guy I bought the car from did not build it. And I could not find the previous owner. Cam and ignition timing are all correct. Checked those before in the past. Valve guides might not be perfect but the motor does not burn oil. About a 1/4 of a quart in 2500 miles. Doesn't smoke on start up or under deacceleration. Inside the engine is really clean too. Compression checked out good. All even @ 135 psi. It's a good motor from what I can tell. The carb needs to be jetted on a dyno but it should not make that big of a difference anyways. Intake gasket is very new too. No leaks. The cam must have a great deal of overlap I guess. Really screams all the way to 6700 rpms. Did some more testing tonight: 15hg/in @1500rpm. 20hg/in@2000rpm. Thats with the pvc too. The pvc system doesn't change the vacuum charactaristics like I thought it would. Seems what ever the motor has for a vacuum measurement it does have a lot of capcity to hold it reguardless of a few leaks in the system like the pcv. A mechanic told me you need 15hg min for the brakes to work properly. Told me to install a canister. Said the canister will hold vacumm using a one way valve. So if I create 20hg/in at 2000rpm it will hold it in the can when needed. In 6th gear around 75 mph I run 2100rpms. This of cousre will be a different throttle opening resulting in less vacuum. Under deacceleration with a closed throttle the vacuum is above 20hg easy so that should help. Close call for sure. We will see if it actually works in reality. A speed shop guy told me someone sells an electric 12V vane type vacuum pump for the booster if needed. Anyone ever heard of that before? The Good news: Through testing I discovered my pcv system works great and I can keep it in operation. It's effect on the overall vacuum capcity is next to nothing. Quote Link to comment Share on other sites More sharing options...
Brad-ManQ45 Posted January 8, 2006 Share Posted January 8, 2006 ZXT's used vacuum pumps to insure they had vacuum to work the cruise control. Haven't heard of the pump you're tal;king about, but no reason for it not to work. Doubt you'd need it though... I'd be worried about that 8" though.... Quote Link to comment Share on other sites More sharing options...
buZy Posted January 11, 2006 Author Share Posted January 11, 2006 I found this electric booster from summit. http://static.summitracing.com/global/images/instructions/ssb-28146.pdf Quote Link to comment Share on other sites More sharing options...
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