Edelbrock and PCV

[green1]

440, 750. Is the big port on the front un-ported? or do we need to feed PCV from manifold?

 

[fugly]

big port on the back (May have a setscrew in it) or the intake

 

[the wall]

un-ported would mean constant vac, then yes that were the pcv goes and if you do put it in the manifold it needs to go in the plenum area under carb not in a runner

 

[Meep-Meep]

The 3/8 nipple on the front or back is for PCV.

 

[plymouth67]

It is the one on the front and when you are full throttle it closes the pcv valve like it should. At that full throttle your motor vents through the breathers in your valve covers.

 

[74sundance]

Front port is for the PVC ....The rear is for power breaks...
Here it is rite from the horses mouth:

Click carb install part 1

http://www.edelbrock.com/automotive_new/misc/tech_center/install/tech_vids.shtml

Or here is a direct link to the video:

http://www.edelbrock.com/automotive_new/misc/tech_center/install/dl/Installation_PT1_320.wmv

 

[green1]

Thanks.

 

[fugly]

There are two reasons for putting it in the back-one is simply looks, the other is performance- the last thing you want on a performance engine is the pcv to stop working at high rpm-it helps keep the crankcase from building pressure...kinda like a mini vacuum pump

 

[696pack]

There are two reasons for putting it in the back-one is simply looks, the other is performance- the last thing you want on a performance engine is the pcv to stop working at high rpm-it helps keep the crankcase from building pressure...kinda like a mini vacuum pump

Either you didn't read two post up from your or you simply disagree and don't understand what it does if you use the unported vacuum port at the back of the carb. Too much vacuum (unported) will suck oil out of the engine. This will not only make your car use an excessive amount of oil but will also foul your plugs. DO NOT use this port for your PCV.

 

[Cranky]

Maybe reading this will shed some light on how a PCV systems works http://www.aa1car.com/library/pcv.htm and Fugly knows what he's talking about....

 

[67 B-body]

Either you didn't read two post up from your or you simply disagree and don't understand what it does if you use the unported vacuum port at the back of the carb. Too much vacuum (unported) will suck oil out of the engine. This will not only make your car use an excessive amount of oil but will also foul your plugs. DO NOT use this port for your PCV.

I hope it's baffeled in the valve cover.

 

[696pack]

Maybe reading this will shed some light on how a PCV systems works http://www.aa1car.com/library/pcv.htm and Fugly knows what he's talking about....

First, I now see you and I are discussing this in two different threads.:grin:

I am fully aware of how a PVC operates. when it is fully opened at high throttle IF it is hooked to and UNPORTED (un-metered) and larger opening like the back fitting of this carb it is going to suck oil out of the engine just like will if the PCV will if the valve cover is not baffled.

I went through all of this years ago and learned it all the hard way when I had a mid year Corvette with a 350 engine and tried to run the Corvette factory ribbed valve covers (prior to 68) with no PCV provisions as the earlier 327 blocks had a draft tube.

If Fugly know what he is talking about then he should know this and it is also stated (by Edel.) that the rear larger port is for power brakes and if not used for that purpose is to be plugged. The ported vacuum and much smaller fitting is for the PCV.

Yes, I agree that you need the PCV working at high RPMs but you also don't want too much suction that is sucking oil from the crankcase rather than just fumes. If it is then it is going to foul plugs and one of the reasons for an exhaust dump system that by passes the engine. This is why on the Edel. carb being discussed the front port is metered.

 

[74sundance]

I got this from Edelbrock:

Q: Can I run my PCV line to the rear of the carburetor?

A: We do not recommend routing the PCV line to the rear of the carburetor. We recommend that the PCV line go to the front, if you have power brakes, they go to the rear.

.......Also if you read the manual it say's to connect the PCV to the front port.

 

[Al K]

Good thread;now I'll further confuse the issue...

If both covers have openings for breathers,should:

1)Both breather caps be of the PCV-type?
2)One be PCV and one normal?
3)Both be routed to the (front) fitting? Or...
4)One(PCV) to the fitting and one to atmosphere?

I've got both "T"-ed into the front fitting. One breather is PVC,the other is "normal". Both covers have baffles under the opening(s).

I know I'm not the only one who has wondered about this.

 

[fugly]

Either you didn't read two post up from your or you simply disagree and don't understand what it does if you use the unported vacuum port at the back of the carb. Too much vacuum (unported) will suck oil out of the engine. This will not only make your car use an excessive amount of oil but will also foul your plugs. DO NOT use this port for your PCV.

Well, since (according to you) I don't know what I am talking about, I thought I might disagree.....There are a few holes in your theory -if you will refer to the pic below you will see two red areas- these are where the front and back ports feed from

The right one is the secondary , left primary- you will note they both pull from beneath the throttle blades meaning NEITHER one is ported. They are both drilled straight thru with no mechanism to close them at any throttle setting. Also, there are at least two methods of plumbing a pcv system- one is to the carb/intake from the pcv with an open breather on the other cover, referred to as an open system, the other uses a tube to the air cleaner instead of an open breather, referred to as a closed system. At WOT there is little to no vacuum (with a properly sized carb). The PCV valve is weighted or spring loaded and designed to close in no vacuum situations ( such as engine turned off) and depending on amount of vacuum, varies the amount of blowby passed. The closed system allows the gas to back flow thru the aircleaner at low vacuum situations (such as wide open throttle)- in a high performance engine this allows for some scavenging due to the slight vacuum created by high velocity in the aircleaner ( and is better for the enviroment if that is a concern) By design and placement the valve is designed to control oil and if your valve covers are properly baffled , there should be no liquid oil flowing anyway- I also like to plumb PCV or vacuum pump systems from the front of the valve cover since under acceleration, the oil will naturally try to go to the back. Also, the front port is a fixed size and the rear one can be fitted with a variety of nipples thereby allowing it to be sized to the hose used if necessary...hope this allows you to understand my stupidity....

 

[696pack]

fugly,

My comments to you were directed/based on what the manufacturer states in the links above in this thread about THE carb that is the subject of this thread AND my personal problems with this same issue with a Holley on a Corvette.

The question was "Is the big port on the front un-ported? or do we need to feed PCV from manifold?"

The video link from Edel. for installation shows a Camaro with power brakes and states that "the rear port is for power brakes and the front port is for the PCV but since on this car they are working on has the power brakes plumbed to the manifold so the rear port on the carb needs to be plugged." Since they specify where things are to go they must have a reason.

I was not calling you stupid or any other names and simply stated that you either didn't read (and look at) the link OR that you disagreed with it. If you disagree then I would think that you would give a particular reason that the Edel. instructions are wrong.

I have not had one of these carbs apart at the front PCV port but would ASSUME that they have a metering valve there. It has been 15+ years that I had the problem with the Corvette but if I remember correctly I had to install some kind of metering for the carb I was working with at the vacuum source.

 

[fugly]

I have modified literally hundreds of these carbs for everything from street, to drag and circle track- there is no metering valve in the front- it is drilled sideways and down to the red space just like the rear- the accelerator pump squirter passages are directly above there- I did not say Eddy's instructions are wrong, but I don't like a bunch of hoses in the front- it looks messy.....IF there are power brakes it may be debatable to hook the brakes and PCV to the back, but otherwise the ports function exactly the same

 

[the wall]

fugly is correct it can go in the front or the rear on the large port. the pcv valve is the vac regulation not the port if you are sucking oil from the engine then your pcv valve is located improper or valve not baffled proper or the oil is being trapped in were the pcv is located. the pcv valve shuts itself off when the vac level in the manifold get below a value in the pcv. just about all brake booster line come from a runner in the manifold but they can be installed at the base of the carb.

 

[74sundance]

We all have the same interests here guy's, lets keep it the easy going forum we all love

 

[696pack]

Hey, if I am wrong I am wrong. Just that Edel. shows it belongs in the front and that is what the OP asked.