I know we hit some of this in the other thread... Please explain exactly how the PCV system works, and why it is not needed on both sides. What would running on both sides do and would it hurt or help? It would seem that you would want the same vacuum on both side of the engine??? Also, Should I run the line to the front port on my carb (Edel 1406), to some port on the manifold, or does it make any difference. There is also a plugged port on the back of my carb, can I use it instead of the one in the front, just to keep it cleaner looking? Why is there even a valve on the pcv? Is it a one-way valve, and if so what is it blocking and which way. How often does it need to be replaced, and what is wearing out on it to make it need replacement? Some cars have a hose going to the air cleaner...is this also pcv, and if so, it there some reason it goes there rather than the carb (or manifold)? Just wondering... (It is raining like crazy today, and I don't want to be stuck in the house, so I am trying to think of a simple project I can do in the garage without having to run the engine )
first, there is no divider inside the engine. vac at one valve cover affects the other. most '60-'70s setups involve one vc going to carb, one to air cleaner. at low eng speed the vac takes the vapors into the manifold. as rpm goes up, you dont want to suck oil, so pvc valve closes, but now air thru air cleaner is fast enough to draw the vapors; if i remember correctly. early mustangs had a road draft tube which went from one vc down near the ground so air going by took the fumes. pvc is all about fumes venting into/not into air; not improved performance. if pvc valve sticks it can hurt operation/ how it runs.
On my 73 with the 302 the pcv valve has been done away with, as well as anything running to the air cleaner. The pcv valve simply recycles fumes instead of dumping them, and isn't really necessary, but I believe it will never pass emissions again if done away with. On my 74 with a 250 it seems to be completely stock. I've got a hose running from the oil cap to the back of the air cleaner, which I've always assumed is the pcv valve, and is necessary unless you want it smoking underneath your car. I have intentions of replacing the air cleaner and valve cover/oil cap eventually and doing away with it as well, since it just looks bad. The reason it goes to the air cleaner is emissions-related, I'm sure.
http://en.wikipedia.org/wiki/PCV_valve I hope you change your oil very often. On a stock engine, the PCV will not make any diffrence in performance assumeing it is intact and working correctly.
You got it that way, so that makes it right? Aside from an all out drag car or trailer queen show car that rarely sees use, at what point does appearence become more important then function? Espeically on a car driven on the street on a regular basis. And does one simple tube going to the valve cover really look that bad? Do what you will, but personally if there is a system on my engine designed to make it run cleaner and last longer, I choose to keep it intact and in good working condition.
A PCV valve is an emissions-control device, however it does not rob any power whatsoever, so I still use mine. I have it plugged into the driver-side rocker cover and the other side has a hose running to the air cleaner...
Another type of evacuator can be used also. They are designed mostly for drag racing but will improve any engine with headers and running high rpm's. Moroso makes this crankcase evacuator system fairly cheap. consists of two 1/2 x 3in long pipe nipple, cut at a 60degree angle on one end. Two valve cover breathers with hose nipples incorporated on them. Two pieces of 5/8 heater hose and clamps. Finally, two, one way valves that will screw onto the pipe nipple after it is welded into the header collector. This also must be drilled and welded at an angle. The heater hose is attached and run up to the new breathers. The exhaust gases flowing past these valves creates a vacumm effect and draws all the fumes and excess oil vapors, etc. out of the crankcase and valve covers, then they are usually burned and blown out the collector and/or muffler and pipes. Parts for this can be purchased seperately at hardware and auto stores, if you want to make a set yourself. I have the part # for the one way valve if you need it. Seems to help purge any pressures in all our race enigines, but may not be legal on a street driven car, in some states. Just a thought on the subject.
Actually, you need both sides open. The airflow circulates much like a cooling system does. One side is a fresh air intake, the other is the exhaust. Circulating fresh air into the engine is good for it, and it help reduce condensation, which fouls the oil eventually, and contributes to corrosion. If you are running a PCV, and you should on any street car, you should have one side PCV and one side vented. There is really no downside to running a PCV system.
Honestly, more than anything it's a lack of knowledge on my part. I know PCV systems have something to do with emissions -- and that's it. I didn't see it's right, I said it looks nicer. All I said was that my 302 didn't have a PCV system. After reading what I have here, I definitely won't be changing the PCV setup on my 250. This whole thing is a learning expereince for me, so bare with some of my ignorant comments. Steve
No. I have an aftermarket oil filler cap on my car with intergrated breather/filter. It works fine. It dosen't really matter where the breather goes as long as it has a filter of some sort on it.
If it's connected to the large, full manifold vacuum port of the carb. As described above, the manifold vacuum, which is high at idle and part throttle draws the blowby gases (burnt and unburnt) out of the crankcase that would cause acidic oil, sludge, and pollution. The vacuum created in the crankcase by this action draws in fresh air from the opposite valve cover. Of course you want the fresh air to be filtered so dirt doesn't get inside the engine. That's why a filtered breather or a hose from the inside of the air cleaner is used to supply the fresh air. PVC systems are a good thing.
One other thing a PCV system does is reduce pressure inside the engine. With pressure inside the engine it will cause oil leaks anywhere that does not have more pressure on the sealing surface than inside the engine. Many times I have fixed oil leaks on engines simply by replacing stuck or clogged PCV valves. Fuel injected mustangs are the worst due to the fact that they have a filter under the PCV valve that gets clogged up. The PCV system is a very useful part of any car. All modern engine designs have some sort of PCV system on them.
