Chevy Nova Forum banner

1 - 20 of 26 Posts

·
Premium Member
Joined
·
15,966 Posts
Discussion Starter #1
This is example how something simple can cost you big!

This is what happens when a engine is not ventilated correctly.
This engine used a lot of oil in a 300 mile run on the hwy.
Lost oil pressure and major repair. owner elected to replace the engine.

Please take note of the 2 PCV valves, They are not even hooked up to a vacuum source. They are in both valve covers. And do not allow air in, and restrict air flow out.
this was a big mistake, as the engine must have air in and out. The ventilation process reduces crank case pressure. High crank case pressure causes leaks, blows gaskets and causes high oil consumption as in this case.

YOU MUST HAVE FRESH AIR IN, and a positive controlled Vac source to ventilate the engine.

This engine had no vent, no vacuum source. The old valve covers were plugged with a PCV valve each without a vacuum source.

If this had been a original 327 with the block vent out the back the engine would have been ventilated. This is a 350 engine and no vent.



Also take note of a copy from a Motors manual on how the engine vent system works.
 

·
Premium Member
Joined
·
2,733 Posts
Good basic info everyone should know. I have heard that some race motors use two breathers on the valve covers instead to reduce the force from the pistons pushing on the air in the case, I guess this way it can more freely flow in and out to allow the pistons less restriction.
Any word on whether this holds any water?
 

·
Premium Member
Joined
·
7,437 Posts
I would also be curious as to why a 'Thermac' (vacume operated 'air door' within the air cleaner snorkel) was placed into use (or not in use) on this particular engine "configuration"..??? If the Thermac was not operating correctly (or at all) even more air flow was restricted... :rolleyes::confused::rolleyes:
 

·
Premium Member
Joined
·
3,257 Posts
Good basic info everyone should know. I have heard that some race motors use two breathers on the valve covers instead to reduce the force from the pistons pushing on the air in the case, I guess this way it can more freely flow in and out to allow the pistons less restriction.
Any word on whether this holds any water?
I don't know if that holds any water. Anytime one piston is moving down "pushing air" there is another one moving up at the same time "pulling air". Seems to me this would balance out the "air" effect.
 

·
Premium Member
Joined
·
7,437 Posts
Mainly done on full race engines due to the high pressure within the valve covers.. A one way valve (like a PVC) is placed in line and the pressure is evacuated through the exhaust collector...
The old engine of Tim's that Al is depicting appears to just be a mess of left over emission devices doing more harm than good...
 

·
Registered
Joined
·
609 Posts
while on the topic,

whats your opinion of PVC on a drag race engine or circle track engine?

Ive been having this discussion with a few guys for a whole season.
I run a PCV from my left valve cover on my dirt track truck. I know i need it but anyone have an opionion?
 

·
Premium Member
Joined
·
15,966 Posts
Discussion Starter #7
Good basic info everyone should know. I have heard that some race motors use two breathers on the valve covers instead to reduce the force from the pistons pushing on the air in the case, I guess this way it can more freely flow in and out to allow the pistons less restriction.
Any word on whether this holds any water?
I run dual vents with pan-a-Vac on both sides.


Click on pic for better detail
 

·
Registered
Joined
·
1,179 Posts
On our 410" Sprint car engines, there are no valve cover breathers. They only have one breather and it is located about where the coolant outlet would be on the front of the intake manifold on a street engine. The engines have a dry sump oil system so they pull a vacuum, I assume that's why there's no breathers on the valve covers...

pops
 

·
Premium Member
Joined
·
15,966 Posts
Discussion Starter #10
Al... Who makes that stat-housing cover/temp gauge ??? Or did you make it yourself ???
I made it, Moroso water outlet.
I have a few of those gauges left. :yes::D

Al
 

·
Registered
Joined
·
932 Posts
whats funny...............l when l was first starting out had 2 PCV valves had them BOTH on VACUME about 50km later BOOM l CRACKED IN HALF a 350 ROCKET 4bolt F-ked it right up....l was 10yo lesson learnt we wondered why the oil pressure was so high and it was running so smoothly
 

·
Premium Member
Joined
·
2,858 Posts
What is the best way to set up a PCV for my engine?
From one valve cover to the back of the manifold?

Any pics and details appreciated.

 

·
Premium Member
Joined
·
7,437 Posts
What carb do you have ?? You probably have a port near the baseplate..
If so., you can use that, & then go to a different breather on one valve cover that includes a nipple for a hose and also has a PCV valve... Or you could remove that breather entirely and replace it with a suitable grommet & PCV valve...
 

·
Premium Member
Joined
·
15,966 Posts
Discussion Starter #15
Why do you have that carb on a dual plain intake?

If that is a air gap intake it has a port in the back of the intake.

Al
 

·
Premium Member
Joined
·
15,966 Posts
Discussion Starter #17
On many early 60s cars with 327s, stock setups, I see no breathers or pcv in valve covers. How did they do without it?
they had a vent under the intake that came out the back of the block.

Al
 

·
Moderator
Joined
·
14,584 Posts
Are valve cover breathers more effective? Under the intake ventilation would sure look better than all the holes and hoses.
If I remember right the EPA/gov. had something to do with that. They did not want all of the emissions just being dumped out of the vent pipe. They wanted the emissions controlled. I remember seeing a lot of the old cars when they were running having a cloud of smoke come up from under the car from the block vent pipe.
 

·
Premium Member
Joined
·
7,732 Posts
If I remember right the EPA/gov. had something to do with that. They did not want all of the emissions just being dumped out of the vent pipe. They wanted the emissions controlled. I remember seeing a lot of the old cars when they were running having a cloud of smoke come up from under the car from the block vent pipe.
It sounds like you're thinking of the older draft tubes. Early 60s Chevy small blocks used a PCV valve. There was a baffled port in the rear of the engine that a rubber hose attached to it that ran to the PCV valve which was screwed into a vacuum port in the carb. The intake then had a breather in the front.

These are the 1st generation "open" PCV systems. If the PCV valve goes bad or the hose starts to leak, you get oil and crud all over the intake and engine compartment that comes out of the front breather from the blow-by pressure. Just like it will come out of a breather on a valve cover if the same thing happens.

The later "closed" PCV systems used in-line PCV valve connected to a vacuum port on the carb and then the breather actual runs through the air filter. This further reduced emissions some more while still accomplishing the crankcase ventilation.
 
1 - 20 of 26 Posts
Top