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Username Post: Vacuum & PCV        (Topic#202375)
apache31 
Contributor
Posts: 492
apache31
Loc: Northern California
Reg: 09-09-07
11-02-08 09:31 PM - Post#1555693    

383ci Vortec
Carbureted
TH400

I had a baffled style grommet in my rocker cover connected to a pvc valve. The thing swelled up to twice it's original size. Here are two pics if you're curious. I've never seen anything like this before.

Swollen pvc grommet 1 Swollen pvc grommet 2

Question:

Could this swollen grommet be in a failed status and be sucking oil into my manifold and hence the reason I seem to be running rich??? Black stuff out the tail pipe, etc. No fouled plugs though but they are dark.

Next:

I changed it out for a new one of the same style. What I noticed:

1) The new one really restricts the air
2) Seems like the engine runs stronger/faster now.
3) Engine idles slower now with the new grommet.

I've been reminded that a pvc is a controlled vacuum leak. Should that pcv be flowing air pretty good or should it be on the restricted side?

Confused on whether the engine was breathing better with that old grommet in there or if it is in better shape now with this restricted one. If vacuum leaks are not good, then shouldn't I stay with this restrictive grommet.

Side note, the pcv itself seems to be pretty free-flowing.

Not even sure which pcv I should be using.



"It was made to drive..."
1959 Chevrolet Apache 3100
My Truck Pics


 
IgnitionMan 
Valued Contributor
Posts: 2639

Reg: 04-15-05
11-02-08 09:40 PM - Post#1555700    
    In response to apache31

What were the numbers identifications on both the valve plates inside the valve, new one, old one? Different ident, different vacuum operating rating/volume flow.

To see the ident markings, look inside the valve on the ENGINE end, the plate inside the body. Could be one number, one letter, combination of them.

Example: early 275 horsepower 327, with high idle vacuum, may use a valve marked "2", 1966 425 horsepower, lower idle vacuum, "6". Different loadings for different vacuum levels/flow bypass rates.

The one on my all aluminum, bored and stroked 322 inch Rover V8 in my 1972 Vega uses a 90 degree bend valve marked "3", and, a restrictor plug in the line from the valve, with a .075 hole in it. That is what the engine liked best.

Edited by IgnitionMan on 11-02-08 09:40 PM. Reason for edit: No reason given.

 
Petroholic 
Contributor
Posts: 839
Petroholic
Loc: Moses Lake, Wa.
Reg: 08-12-05
11-02-08 11:08 PM - Post#1555728    
    In response to apache31

Wouldn't oil create more of a "blue" smoke?



 
apache31 
Contributor
Posts: 492
apache31
Loc: Northern California
Reg: 09-09-07
11-03-08 11:33 AM - Post#1555995    
    In response to Petroholic

IgnitionMan - i will check that.

Petro - yeah, that makes sense. I really don't see smoke at all coming out of my tailpipe. It just smells strongly of exhaust but when it is idling to warm up there are two black spots on the garage floor.
"It was made to drive..."
1959 Chevrolet Apache 3100
My Truck Pics


 
apache31 
Contributor
Posts: 492
apache31
Loc: Northern California
Reg: 09-09-07
11-03-08 02:22 PM - Post#1556089    
    In response to IgnitionMan

It was the grommet that made the difference not the pcv valve. I only changed the grommet. The new one is more restrictive than the old one and they are identical Mr. Gasket baffled grommets. The old one was swollen and distorted and more pliable as a result and that's probably the reason it was so free-flowing. The new one is more restrictive, tighter. These grommets have a little slit in them that is stepped - I assume that's what makes them baffled.

As for pcv valves, the one I have installed does NOT have any I.D. numbers on it. It's housed in one of those purdy polished alum housings. I pulled it and no numbers shown.

I got a hold of a Chevy Dealership and the part number they put on their 383 performance motors is the same one GM has used for years. GM # 6487779 Delco # CV774C

I guess I can try the GM valve and see if there is any difference. Is this the one you are using?

I guess I am wondering what standard do I use to measure if the "engine likes it better" or not (to use your words)???

I could trash these Mr. Gasket grommets altogether, cut me a piece of stainless steel and screw it to the back side of the rocker cover to act as a baffle and THEN install the GM pcv valve. This way the grommet would not be causing any restriction and the effect would be isolated to the pcv.

Again, don't know how resrictive or not the pcv should be and what I use to measure if the engine "likes it better."
"It was made to drive..."
1959 Chevrolet Apache 3100
My Truck Pics


Edited by apache31 on 11-03-08 02:32 PM. Reason for edit: No reason given.

 
IgnitionMan 
Valued Contributor
Posts: 2639

Reg: 04-15-05
11-03-08 07:24 PM - Post#1556365    
    In response to apache31

I used to go down to my local Pep Boys store, and, look at all the after market specs and valves, there is where I got the numbering system, NOT from OEM stuff. Nice thing was, all those valves were skin packaged, clear plastic, do, all you had to do was go find an engine that had roughly the same size and vacuum level, look at the right valve for it, and, the number.

 
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