1976 280Z Restoration Project

[ramsesosirus]

On 7/25/2019 at 6:24 PM, wheee! said:

A little more engine bling. Couldn’t resist the beginner badge!

 

Correct me if I'm wrong, but I thought having those "mini air filter" breathers is bad?  (vs having them routed somewhere via hose)

[siteunseen]

13 hours ago, wheee! said:

Too late. They’re already powder coated and polished. I’ll find a use for them...

[wheee!]

1 hour ago, ramsesosirus said:

Correct me if I'm wrong, but I thought having those "mini air filter" breathers is bad?  (vs having them routed somewhere via hose)

Normally yes, they can change the amount of un-metered air that is entering the engine. However, I am using an Idle Air Controller with the Haltech system which should monitor the MAP (along with the vacuum line straight to the ECU) and control the combustion process more accurately.

I could route the hose down and over to the oil catch can that is re-routed back to the PCV valve under the intake manifold, but for now the only line going back to the intake through the catch can is the crankcase vent.

[Zed Head]

32 minutes ago, wheee! said:

I could route the hose down and over to the oil catch can that is re-routed back to the PCV valve under the intake manifold, but for now the only line going back to the intake through the catch can is the crankcase vent.

If the PCV valve is still connected you'll have a straight shot of outside unmetered air through the valve cover and through the crankcase to the intake manifold, carrying oil vapors with it.  The system is designed to be balanced, with only metered air or combustion byproducts in the intake manifold.  Better, I think, to block the PCV valve opening and just use the breather as a vent, like it was in the old days.  As the engine wears and you get blow-by you might find the breather blowing oil vapor at high revs.  Or even early in break-in while the rings are seating.

[240260280]

Why did I start drooling 2 posts ago?

[wheee!]

4 minutes ago, Zed Head said:

If the PCV valve is still connected you'll have a straight shot of outside unmetered air through the valve cover and through the crankcase to the intake manifold, carrying oil vapors with it.  The system is designed to be balanced, with only metered air or combustion byproducts in the intake manifold.  Better, I think, to block the PCV valve opening and just use the breather as a vent, like it was in the old days.  As the engine wears and you get blow-by you might find the breather blowing oil vapor at high revs.  Or even early in break-in while the rings are seating.

The Crankcase vent will go to the oil catch can, and vent back to the PCV valve. The valve cover will allow fumes to vent out and allow air to come in under varying valve cover pressures. I know it's not perfect, but this combination is what has been run with the haltech systems for a while now with no ill effect. I do realize that the oily residue may start to come out of the breather on top... so eventually I may route this to the catch can too. I will see.

[Zed Head]

With the passage to the intake manifold open at the PCV valve there will always be high flow through the crankcase to the valve.  The valve cover is really just an air filter for that unmetered air.  It's only going to act as a vent if blow-by overwhelms the PCV valve.

All I'm really saying is that the PCV system was not designed for constant high flow rates.  It's a giant vacuum leak with the breather on the top.  

Sorry, I'm a little bit robotic on the logic stuff.

How much oil do those guys catch in their catch cans?

[wheee!]

1 hour ago, Zed Head said:

With the passage to the intake manifold open at the PCV valve there will always be high flow through the crankcase to the valve.  The valve cover is really just an air filter for that unmetered air.  It's only going to act as a vent if blow-by overwhelms the PCV valve.

All I'm really saying is that the PCV system was not designed for constant high flow rates.  It's a giant vacuum leak with the breather on the top.  

Sorry, I'm a little bit robotic on the logic stuff.

How much oil do those guys catch in their catch cans?

The PCV valve will be closed most of the time, only open under high vacuum and then it will draw air from the filtered catch can reservoir. That catch can is then pulling the crankcase fumes out under vacuum. The open vent on the valve cover is an issue under high load I suppose, as the tendency will be for some blow by to occur. Under idle and cruise, I expect a small amount of air to be drawn in under vacuum, but again, even Haltech say this is not an issue worth addressing for most applications. I can always route the valve cover to the air intake if i need to, thus replicating the entire factory setup with a catch can in line to avoid most of the oily residue. I am primarily trying to keep any oil out of the intake runners and valves.

[w3wilkes]

on a carburated car isn't the stock design for the valve cover just a hose connected to the back plate of the air cleaner with nothing regulating airflow either in or out of the valve cover? So on a FI car the airflow must be controlled somehow or is it also just attached to the air intake? On a carburated car I can't see that there's really any difference between the stock routing to the back plate of the air filter vs just a little directly attached air filter to the valve cover. Or am I missing something?

[Zed Head]

Lots of things "work".  Without good feedback of air flow to the Haltech computer the system will vary between lean and rich.  I think that it will not be a clean-running engine.  Kind of like a carbed engine.  EFI is about precise air flow measurement and metering of fuel appropriately.  I'm saying that it could be better.

Haltech sells Haltech.

[wheee!]

 

54 minutes ago, w3wilkes said:

on a carburated car isn't the stock design for the valve cover just a hose connected to the back plate of the air cleaner with nothing regulating airflow either in or out of the valve cover? So on a FI car the airflow must be controlled somehow or is it also just attached to the air intake? On a carburated car I can't see that there's really any difference between the stock routing to the back plate of the air filter vs just a little directly attached air filter to the valve cover. Or am I missing something?

The FI cars send the air from the valve cover back to before the throttle body so the air coming in gets metered along with the fresh.

49 minutes ago, Zed Head said:

Lots of things "work".  Without good feedback of air flow to the Haltech computer the system will vary between lean and rich.  I think that it will not be a clean-running engine.  Kind of like a carbed engine.  EFI is about precise air flow measurement and metering of fuel appropriately.  I'm saying that it could be better.

Haltech sells Haltech.

I agree Zed. I am not disputing how things should work. I keep hearing how the airflow balance from the valve cover is negligible, but obviously it was significant enough to have Nissan engineer it into the throttle body air flow. Maybe that was also part of the environmental concerns at the time to ensure oily gases got recirced.

It would be no big issue at all for me to recirc it into the air intake before the throttle body. It would just add an unsightly hose to the top of the engine which I was trying to avoid. I also have a valve cover, if anyone remembers, that has the vent facing the firewall at the back of the driver side of the valve cover. That one is chromed.

Edited July 30, 2019 by wheee!

[siteunseen]

They rerouted that in '78 to keep the oil from stickying up the throttle plate.