Originally Posted by 540 RAT

So if people want to run a PCV system, there is nothing wrong with doing that, other than you will lose a bit of performance. And for those who don't want to run a PCV system, in order to gain a little performance and simplfy things under the hood, there is absolutely nothing wrong with that either, other than causing a bit more pollution. So, pick your poison, either one will get the job done. They are just two different ways of doing things. This stuff is not rocket science……………….

Originally Posted by Durango_boy

Can these losses and gains of performance be measured? Lots of good info and history...but what percentage of overall power are we talking about? The PCV valve and tube is relatively small compared to the amount of air drawn in by the intake. Would a chassis Dyno even show the difference?

Originally Posted by Durango_boy

Can these losses and gains of performance be measured? Lots of good info and history...but what percentage of overall power are we talking about? The PCV valve and tube is relatively small compared to the amount of air drawn in by the intake. Would a chassis Dyno even show the difference?

Originally Posted by 540 RAT

For those who wonder why anyone would NOT want to run a PCV, consider the following:

Old road draft tubes could hardly be said to produce negative crankcase pressure. They are merely bleeding off crankcase pressure like ordinary breathers until you get up enough road speed to produce any delta P at all, and even then it can't be called much suction, more like fresh air being gently drawn in, at best. And high performance Japanese motorcycles that make way more hp per cubic inch than most of our stuff ever will, and that turn more rpm than most of our stuff ever will, for decades used only single vent tubes to simply prevent crankcase pressure from building up. They had no intake vent at all, they just simply couldn't build up any crankcase pressure. There was no ventilation flowing THROUGH the crankcase at all. Though they've changed now in more recent years due to emissions requirements. A PCV system does nothing to really help an engine per se, it really only helps overall emissions, which is why it was originally designed. Without it, blow-by would simply be released into the atmosphere, which has been a big no-no for decades, for cars, and more recently for motorcycles. A lawnmower is another simple example of not having a PCV, the same thing as the older motorcyles just venting to atmosphere. A PCV is also not the main mechanism to get rid of moisture, hot oil above 212* does that by boiling off the water. That's why numerous short cold running trips is harder on an engine than highway driving, because the short trips don't get the oil up to temp for long enough to boil off the water.

Race engine builders use crankcase vacuum pumps in order to use low tension rings for less drag and that vacuum pump helps those rings stay in contact with the cyl walls to retain cylinder pressure, thus making more hp. They do not use it for crankcase venitlation, they use it for crankcase vacuum - big difference. There can be NO crankcase ventilation flow if a vacuum pump is to work. There can't be any CRANKCASE INTAKE VENT on those setups, because they have to create a suction of around 10 to 15" of vacuum, and there could be no suction if there is an intake vent. If there was an intake vent, they would not be able to create any vacuum at all. Here is a statement from a vacuum system supplier:

"Vacuum leaks in the crankcase, valve covers, distributor base, timing chain cover, oil dipstick, etc. reduce the amount of vacuum you will generate. You can easily check your engine by pressurizing it with air, be careful though, you don't need much to find leaks and you could damage gaskets and seals."

Here they are splitting hairs to prevent any vacuum leaks that would affect how well the vacuum system can work, so its easy to see that an open breather that would allow actual ventilation air flow, would render the vacuum system useless. This is a positive "vacuum" system but NOT a "ventilation" system at all. It's the same sort of thing with a header extraction system, only it is much weaker than a vacuum pump, and this one really only works at higher rpm. It also cannot have any crankcase intake vent or it else it couldn't work either.

Positive crankcase ventilation is not imperative to ring sealing and power production. Rings seal because of combustion pressure getting behind them and forcing them out against the cylinder walls. That's why ring side clearance is important, so that the pressure can get behind the rings to push them out. Race motor pistons have a series of holes drilled in their tops just behind the rings, precisely for the purpose of getting max pressure behind the rings for optimum sealing.

Most hardcore hotrods and many sportsman race cars just use two breathers to vent the crankcase, and they have run just fine for many many years that way. Those engine's don't typically smoke or use oil either, if they are in reasonable condition. And two ordinary breathers will increase performance somewhat by elimination of the engine sucking spent blowby exhaust gases back into the combustion chamber, that a PCV would provide. A totally fresh mixture makes more hp, so not having a PCV does solve the problem of a PCV diluting the incoming charge. And you don't have to be Warren Johnson to appreciate this, because most hotrodders want to get all they can out of their engines. You also don't need to have low pressure on the bottom side of the pistons for high rpm power. The pressure difference between a few inches of vacuum from a PCV and atmospheric pressure, is negligible to say the least, when compared to the enormous pressure above the piston. Consider a stout big block hotrod's combustion pressure which would typically be somewhere around 1,200 psi, and that is what pushes the rings out against the cylinder wall as well as pushing the piston down. So, a few inches of vacuum beneath pistons would do nothing compared to that. Not only that, but any teeny tiny gains you might theoretically make when the piston goes down with the aid of vacuum, you'd lose when the piston goes back up against vacuum. And besides, you always have pistons going up, while others are going down, for no net gain with regard to that idea anyway.

So if people want to run a PCV system, there is nothing wrong with doing that, other than you will lose a bit of performance. And for those who don't want to run a PCV system, in order to gain a little performance and simplfy things under the hood, there is absolutely nothing wrong with that either, other than causing a bit more pollution. So, pick your poison, either one will get the job done. They are just two different ways of doing things. This stuff is not rocket science……………….

Originally Posted by zwede

Lars got it right (as usual). One additional thing:

The PCV air circulation also removes condensation from inside the engine. If you only have a PCV valve and no breather there is very little circulation so condensation builds up inside the engine. Not good.

Originally Posted by Durango_boy

Can these losses and gains of performance be measured? Lots of good info and history...but what percentage of overall power are we talking about? The PCV valve and tube is relatively small compared to the amount of air drawn in by the intake. Would a chassis Dyno even show the difference?

Originally Posted by zwede

A PCV system is pointless on a dedicated drag car. PCV won't work at WOT (no vacuum), and their cams are so large there is very little idle vacuum.

Then you have people seeing the race cars without PCV and they emulate them... same reason you see street cars with locked out timing. "If it works on a race car it has to be great".

Originally Posted by I'm Batman

I'll be installing a breather cap this weekend...

Originally Posted by zwede

A PCV system is pointless on a dedicated drag car. PCV won't work at WOT (no vacuum), and their cams are so large there is very little idle vacuum.

Then you have people seeing the race cars without PCV and they emulate them... same reason you see street cars with locked out timing. "If it works on a race car it has to be great".

Originally Posted by BigBlockk

The PCV system doesn't really do much of anything at WOT. Not much manifold vacuum at WOT.

As far as performance loss with PCV I'll bet that if you went to the drag strip and made three runs with PCV and three without then shuffled the time slips you couldn't tell which was which.

A functioning PCV system will keep the outside of the engine cleaner. Less time spent cleaning is more time spent driving.

BigBlockk

Later.....

Originally Posted by noonie

SLUDGE
No one has directly mentioned that other than contamination.
It is the direct result of blowby gas contamination breaking down the oil and causing it to gel and form a sludge eventually causing engine failure if left unaddressed.
Car makers have spent endless hours and money in research in perfecting the system and even revising it. Google for it and you will see Porsche, Saab, Toyota, Audi, Chrysler and GM spending big bucks warrantyiung failed pcv systems.

Moot point with real race cars of any kind because the oil is almost always changed after each race.
Engines with pcv vs the earlier road draft last much longer and run much cleaner.
The older motorcycles had very short service life.
Lawn mower engines used the crankcase pressures thru a tube to run a crude diaphragm for a fuel pump.

The working pcv system is the No 1 prevention of engine sludge next to owner maintenance.

These rust spots are from contaminated oil.

Originally Posted by 540 RAT

Some people seem a little misinformed here. PCV systems "do work at WOT", here's why. Keep in mind that atmospheric pressure at sea level is 14.7 psi, so we always have air pressure available. We just need "some" vacuum to create a delta P, which will cause the air to flow from higher P to lower P, just basic physics. And those laws of physics dictate that there must be some vacuum at WOT to provide the delta P, or else the engine can't ingest any air. No delta P, no air flow, no engine operation. Yes the vacuum is lowest at WOT, but it will not be absent.


The PCV valve is at its most wide open position with little or no vacuum on it, much like a Holley carb's power valve. So at WOT we have little engine vacuum on well setup engines, but we have a wide open PCV valve which allows that low vacuum to easily draw on the engines blow by gases. And at the same time those blow by gases are being generated at their highest level, and would try to create a lot of crankcase pressure except that the open PCV valve gives those gases a place to escape. And those gases won't go out the vent end of the PCV system because it goes where the lowest P is, and that is the engine side of the PCV system (the atmospheric pressure vent side is at a higher P than the engine's lower P side). Where does all that spent blow by end up? You guessed it, diluting your new intake charge. Therefore, WOT does not eliminate spent gases being returned to the engine, at all. So, if you run a PCV system you will be reducing the engine's power by some amount, at all throttle positions.

Originally Posted by Durango_boy

Good news. Got a new battery yet?