302 vacuum/PCV questions.

[jasonv]

Hi,

I had my old 74 302 rebuilt and while I was at it I put an edelbrock performer intake, Holley quickfuel 600 carb, and a perftronix flame thrower distributor. Engine has no emissions parts of any sort, never has.

All sounded good until it's time to put it together. Today's big question is the vacuum ports off the heater hose barb behind the thermostat, do I need those? What were they for?

Vacuum advance is straight forward, port on carb to Pertronix distributor.

I'll probably keep the PCV connected just to keep things a little cleaner. PCV valve, oil cap hose, back of carb easy enough. Do I tie that into the port on the back of the performer intake? It's a manual transmission.

 

[jckkys]

Even '74s that were shipped to other places than Cal. had plenty of emissions equipment when new. Cal. vehicles had more than other places. Ideally the PVC should introduce crankcase gases into the A/F mixture near the idle mixture port in the primary throttle bore below the plate. This allows it it mix with the A/F mixture and be distributed equally to the cylinders. Heater hose barbs are self explanatory. That's how coolant is routed to the heater.

 

[jasonv]

Well I stopped being lazy for a few minutes and hit Google quickly and realized the PCV just goes to the carb fitting. The ports on the intake are cylinder specific and you doNt want that for PCV.

 

[jasonv]

So, could it really be so easy? Vacuum line from carb to distributor and PCV line from oil cap to carb PCV intake?

 

[73azbronco]

Yes. Big hose to big fitting on base of carb, little hose base of carb to dizzy.

 

[Broncobowsher]

Pretty close.

PCV is a system, not a part. Fresh air enters the engine and vacuum pulls it out along with blowby. Typical carbed V8 application you have some sort of breather oil fill cap on one valve cover. This may be a hose up to the air filter or a breather on the oil fill itself. But it is not a sealed oil fill. (EFI does things slightly different to account for all the air entering the engine) The other valve cover gets a PCV valve that connects to manifold vacuum. You want these vapors distributed as evenly as possible to all the cylinders. So base of the carb, not to a single intake runner.

The vacuum advance is almost as simple as you make it out to be. The carb will typically have a couple of options for where the vacuum line will fit. Look at the instructions and find the one marked "ported". 99% of the time that is the correct choice for the vacuum advance.

That is the simple street engine vacuum house routing. That should get you reasonably clean and good running.

 

[September 1972]

The PCV system is open if the fresh air source is taken from ambient pressure, outside the air cleaner. If the fresh air is taken inside the air filter or throttle body that's a closed system. Closed is preferred because under high load the venturi air movement across the PCV port helps to evacuate the crankcase better than a closed system.

Watch out, don't trust the breather cap to filter air, always add another low restriction in line filter on both the source and the valve sides.

Ever wonder where that sandy grit comes from inside a valve cover and on the lifter valley? It ain't normal and it's not supposed to be there.

 

[jasonv]

Thanks guys. Couple more detail questions. On the stock system the PCV intake is on passenger side from the air cleaner, correct?

The oil fill cap hose when to my carb.

Where was the valve? We might have removed it several decades ago. My passenger side just had an elbow from valve cover to air cleaner hose.

 

[Steve83]

Click this, read the caption, and follow the first link in the caption:



It doesn't matter which way the PCV system flows through the crankcase - it only matters THAT it flows through. And you certainly want anything going through the crankcase to be filtered, so it should begin either at a dedicated filter, or inside the engine air filter (clean air side).

 

[jckkys]

All this depends on specifics. Ford used very different PCV plumbing over the years. The '74s had a 3/8" PCV nipple on the back of the 2100 carburetor. The 3/8" hose on this nipple was routed to the oil filler cap on the driver side valve cover. The actual PCV valve was plugged into a rubber grommet in the top of the cap. Clean filtered air was sourced at an elbow on the bottom of the air cleaner and routed to the passenger side valve cover at another elbow. This hose is 5/8" diameter. Earlier Broncos with no EGR had the PCV nipple on the back of the carb spacer. Again this is a 3/8" hose that is routed to the pass side valve cover containing the PCV valve. The clean air source is a 5/8" nipple on the top front of the air cleaner. Supplying clean air through an elbow in the filler cap. When EGR was introduced the rear carb spacer nipple was deleted to make room for the EGR valve. The 2100 carb got a 3/8" nipple to supply vacuum to the PCV valve on the DR side oil filler cap. The last '76-'77 Broncos had a 3/8" nipple on the front of the the carb spacer. The PCV valves have a 5/8" side in either valve cover and a 3/8" input nipple., to the carb or carb spacer. The constant is clean air 5/8" hose from the air cleaner to one valve cover through a 5/8" hose and vacuum from the carb or carb spacer to the PCV valve in the other valve cover through a 3/8" hose.

 

[September 1972]

Right, Ford used the breather cap as a filter and the EGR supply should be filtered and it's not which is a source of rock hard carbon particles bombarding the engine. It's a sad fact that when it comes to your money you spent on your truck, Ford wants to see you in a new truck as soon as possible and making a truck that lasts is not in their best interest. Think for yourselves and you will see some stuff that you can improve over the factory design.

 

[jckkys]

I'm no fan of EGR and wouldn't have it in my EB. New EFI vehicles will throw a code if it's removed so at least on new vehicles we're stuck with it. You mentioned Ford, but I know of no maker that does filter exhaust gases before sending them back into the intake.

 

[Steve83]

...the EGR supply should be filtered...

I've never seen an EGR filter on any vehicle. Certainly not something home-engineered.

 

[September 1972]

EGR passages become clogged with carbon to the extent that that it causes drivability issues on some engines, not all. The EGR systems that have large piping don't seem to plug up with carbon, it all ends up in the engine. Carbon is almost as hard as a diamond, in fact a diamond is carbon. A filter would be at risk of coming apart which it not good, and if you bypass it then cylinder temperatures rise which is again, not good.

Offhand, one solution might be to make a corrugated pipe loop so that the gas takes a rollercoaster ride and the associated pressure drop will deposit the carbon on the bottom loops. A 10K spark plug sensor will provide before and after cylinder temp readings. Keeping the engine in perfect tune with special attention given to the cold start equipment and MAP sensors would be one way to minimize carbon infiltration.

 

[jasonv]

thanks Guys I think I got it. My original setup was filtered intake off the air cleaner to rear passenger side and oil fill cap to carb. I got the parts to reproduce that.

I think somebody got EGR and PCV confused.

 

[September 1972]

Don't forget to pop the carb as part of the PCV service procedure. The drivers side of manifold has a deep well cast into the intake. If it's full then oil will enter the engine and build up crud on the back of the intake valve rather than fill the well. Tt holds quite a bit mine was full.

 

[jckkys]

That's odd. Even heavily worn engines with so much blow by that the loss of power necessitates a rebuild or new engine, don't have oil there. The deep well is just the lower plane of a two plane intake. Crankcase vapors from the PCV are blended with the A/F mixture and thrown down to a corrugated floor that is heated by the exhaust cross over. I've seen a carbon buildup but no liquid oil. That surface is just too hot. An oil leak at the valve cover that runs down on the exhaust manifold or top of the the exhaust cross over has the same resulting carbon buildup.
An EGR filter would be good but the routing is cast passages in the intake and carburetor spacer on these engines. Where would a filter go?

 

[Steve83]

Carbon is almost as hard as a diamond, in fact a diamond is carbon.

Pure graphite is pure Carbon, too, and it's soft & slick. But the Carbon black that's in soot isn't anywhere close to diamond hardness. Those 3 common allotropes vary WIDELY in physical characteristics.

The soot you're talking about isn't pure Carbon, and its texture isn't a result of the Carbon in it. It's a result of the carmelized oils in it, and the dry ash, forming a hard varnish that flakes away due to thermal stress, capillarity, and steam.

But none of that has anything to do with the PCV system.

 

[Broncobowsher]

Yea, the new guy has had some odd (and wrong) teachings that he is poorly preaching now.

I was just reading an article about oil (namely clean looking oil with bad contaminates vs. dirty looking oil that is still good, namely diesel engines). It was stating that the black oil is carbon particles, but that is good because they add to the lubricating property of the oil (to a point anyway).

 

[September 1972]

Post a picture of a 72 spacer plate and top view of the intake manifold and I'll show you what I'm talking about.