To PCV or Not to PCV??

Marlin,

the pcv system constantly removes a small amount of the vapors collecting in your crankcase and replaces them with fesh air. the vapors are the partial by products of combustion. when the manufacturers adopted the pcv system back in the '60s, engine longevity was greatly enhanced, engine wear over time was reduced by a very big factor, something like 1/10th of what it had been. I STRONGLY recommend all non-competitive engines should utilize a pcv system.

George

THAT was exactly what I wanted to hear! Thanks George for Your expertise!

All that George said, plus yes --- all PCV valves are NOT the same. There are differences in operating parameters. What differences? Uh, that I don't know.

Next...;-)

Larry

I've noticed the guys with the big horsepower engines keep the PCV function, without recycling the vapors into the carb, by putting a little filter on the valve cover where the PCV valve was. So, extrapolating from GP's information, the crankcase would still get fresh air replacing the vapors, so keeping engine life higher, but not introducing the vapors into superchargers.

Must be that rattling little valve acts as a check valve. This would prevents the sucking of combustible air/fuel mixture back into the valve covers, when there's negative pressure in there, like maybe when starting the engine.

The filter on top of the bad-a.. motors just keeps the engine compartment cleaner, but they leak a little, like when the engine is started and sort of smell bad. I'm keeping my PCV check valve inline to the air cleaner, based on GP's explanation and the smell and vapr factor of the little filters. Some valve covers just come with the little filters, like my buddy's '69 Charger's Edelbrock valve covers came with chrome rectangular filters. I've also seen the PCV valves on just one valve cover. Wonder if it's better to have a PCV valve on each valve cover, like for better crankcase breathing and maybe better engine life. Though experience has taught me engine life is tied most closely to how often the oil is changed and how hard the engine is run. Some teenagers rev their motors lots and to the rev limiter, while cutting costs on the oil changes and their exhaust pipes expell smoke, expensive to repair, rice-rocket, import engine smoke. Lessons to learn for some.... Why do I digress so much??? Which reminds me of another story....

Ron,

yes, the pcv valve is a check valve. it closes during periods of high intake manifold vacuum, such as at idle or during deceleration. a "stuck" pcv valve will cause an erratic idle.

a pcv system should have a pcv valve on one rocker cover, plumbed to the intake manifold or source of vacuum, where vapor is drawn out of the crankcase. the other rocker cover should have a filtered source of fresh air, where air is allowed to flow into the crankcase, to replace the air removed through the pcv valve.

the dual filters you see on some "hot rodded" engines, do not comprise a pcv system, they are just filters to filter any air that may decide to flow into the crankcase. with dual filters, the crankcase is simply being vented to atmosphere, preventing a build up of pressure in the crankcase, which would oppose the movement of the pistons & inhibit power production. there is no force being applied to positively vent the crankcase of vapors. when a long duration camshaft is installed in an engine (you know, the kind that makes a lumpy idle), the intake manifold vacuum at idle is so low that a pcv valve would stay open & therefore can't be used.

which reminds me of another story ...

George

I have the same problem.
When I got my Pantera the PCV valve was connected to the base of the Holley. The rolling road guy disconnected it as it was turning the mixture too lean.
But the stock way of connecting the pipe from the PCV is to the air filter - so it won't affect the mixture (am I right?).
My other rocker cover is connected to the carbon canister - is this so that fumes from the fuel tank go to the canister and then these are sucked out, right through motor, through the PCV, through the carb and then burnt?
(I think I read of something similar on Triumph Stags - but my memory is not reliable).
Is this how it's meant to be connected?
Any recommendations of the best way?

Also - I think I was once told that the oil fumes from the engine can encourage detonation/pinking/pinging - does that sound right?

Positive Crankcase Ventilation: This is the Automotive Industries answer to controlling SMOG and they found out that it helped the rings seal better during the combustion process. Hot rods have since used vacumm pumps to do the same function and bypass the Carb as the pump source and not keep the intake as clean as possible to promote better combustion. Most if not all race engines run a Positive Crankcase Ventilation system to promote ring sealing.

I have been searching through old posts on this forum.
It seems the standard set up is that one rocker cover connects directly to the side of the air filter. The other should go through the PCV to the carb base.
But what about connections on the carbon canister, I guess there should be something to draw off the fuel fumes - but where would it be connected?
The rolling road guy says I have low vacuum at idle so I'm not sure if a PCV is a good idea.
(unfortunately I have no idea what sort of cam is in there - all the history of the car was lost in a fire).

If you have a pcv and fuel injection, do you also need a breather someplace to get airflow thru the crankcase?

The PCV should be connected to the base plate of the Carb, (the Carb is sucking the fumes out of the crankcase). The breather filter media is connected to the Valve cover thru the intake filter attachment on stock intake filter cover assembly. Any connections differing from the above will result in driveability problems, same as a vacumm leak. Hope this helps....

Rapier,
My carbon canister was connected to the vent off the top of the fuel tank.

To answer the question of a few posts prior. One connection must be to a vac source (carb base). Some installs do not use a filter on the valve cover but a hose to the base of the air cleaner. All this does is move the filtered air from a smaller air cleaner on the valve cover to the main air cleaner for the engine. The both work and I have seen both used in OEM applications.

Folks,

I'll try to clear up the charcoal cannister issue. First, it is not part of the pcv system. The charcoal cannister is part of the "evaporative emissions system". The federal test for evaporative emissions the manufacturers had to pass was this: the car sat in a sealed room for 24 hours and the hydrocarbon emissions in the room were monitored and had to remain below a certain level during the 24 hour period of the test.

To pass this test the manufacturers routed the vents from the carburetor fuel bowl & fuel tank into a charcoal cannister that collected the gasoline vapors. The cannister was sized large enough to store 24 hours worth of vapors. A hose from the cannister was then routed to a source that would draw the vapors out of the cannister and into the engine when the car was running. On the Pantera its that small, corrigated, aluminum foil covered hose attached to the side of the air filter assembly. If this hose is missing, your car is not in compliance. I won't tell anybody, I promise. (It won't affect drivability)

Regarding the question of needing a pcv breather on a fuel injected car, the answer is yes, a supply of fresh, filtered air is still needed. you should find that one valve cover will have a hose connected to a point along the intake tract, downstream of the air filter assembly.

George

As I suspected, many of the pipes in my engine bay don't go where they are supposed to.

See the attached picture - I have drawn a diagram of how I think it should be. Many thanks to all of you who know more about this than I do .
Please let me know if my schematic is correct.

I think you've got it..... Check the PCV valve and make sure it rattles, when in doubt purchase a new one, your engine will thank you...

Thanks johrt.
Currently the pipe from to carbon can goes to the right side rocker cover instead of the air filter . I guess the previous owner rerouted to pipes when he fitted the torker, holley 700 and moroso filter.
The only tricky part is that my air filter has nowhere to connect any pipes.
I do have the stock filter - but it doesn't fit under the engine screen anymore.
I'll have a look at it, maybe I can make some holes and fit some grommets to the moroso filter for the pipes.

Does anyone know what sort of PCV valve I need (i.e. what sort of Ford it comes from) - it's not so easy to buy Pantera parts in the UK.
It's the cylindrical push in type that I have.

I have the Fram part number at home, I'll post this evening, unless somebody else has it handy.

George

Rapier,

the Fram pcv valve for the 351C is part number FV156.

Here in the states the Pantera's 351C parts can be cross referenced with the 351C 4V or 351 CJ found in a '71 thru '73 Ford Mustang or Torino. I don't know if that helps at all in the UK.

George

Thanks George.
Yup, that will help a lot. There are a good handful of businesses here that specialise in US car spares - but, as far as I know, no Pantera parts suppliers except the one official DeTomaso dealer.