View Full Version : Frankenstein PCV help

06-12-2017, 01:39 PM
Have a slight annoyance with my Frankenstein PCV set up - any experts (or non experts - :D ) venture to guess what the problem and solution could be?

Carb - Holley P.O.C (ok I won't go there)
PCV incorporated into the base on the primaries.


Line runs from the back of the carb over to the PCV valve on the driver front valve cover.

p/n 2072 cross references to a Fram FV184 which is designed for a Chevy 350 (probably the trouble :D) so figured it was about the right valve for the 352. Similar displacement. Did a lot of complex computations to pick this one (aka - needed the right angle that fit the grommet and this was the one I found).


Fresh air intake filter on the opposite valve cover.
Nothing special - push in style.


System works fabulous until........

Been riding for a while and have to descend a long grade.
Vacuum pressure would be at maximum and I suppose rather than just pulling gasses from the engine it's now pulling oil vapor or actual oil. Can smell it burning through the exhaust.

Was thinking that I could:

* Block off some of the holes in the breather cap to limit intake.

* Find a different PCV valve

* Limit intake with some type of in line restrictor.

* Maybe the system doesn't get enough air through the breather at max vac pressure rather than too much and so adding the in line restrictor would help?

Whatcha thunk?


06-12-2017, 04:56 PM
Do you have a baffle welded into your valve cover (just under the breather cap)?

06-13-2017, 01:17 PM
Good point - no - hadn't thought of that aspect.

It's line of sight straight to the rocker shaft.

Guess I would have to bolt something to a stud on the rocker assembly since welding a proper baffle to the chrome valve cover would destroy the chrome plating.

Will have to study on that - thanks!

06-13-2017, 03:18 PM
As another option, I remember seeing someone making a machined plug that goes in the hole where the factory breather tube was installed. This makes a great place to install a hose with an inline PCV valve. Then you could just put a plug in the hole in the valve cover. If there's any interest, I will try to dig up the info on the breather tube adapter.

06-13-2017, 06:03 PM
That is from the tbirdnest website

06-14-2017, 08:10 PM
[QUOTE=DKheld;108929]System works fabulous until........

Been riding for a while and have to descend a long grade.
Vacuum pressure would be at maximum and I suppose rather than just pulling gasses from the engine it's now pulling oil vapor or actual oil. Can smell it burning through the exhaust.

Whatcha thunk?

The valve cover should be baffled to reduce oil mist or even splash from entering the system, yes. And ideally the breather/P.C.V. orifice will not be inline with any one rocker arm, which would tend to increase the difficulties with direct splash. Also attempt to route hose lines "uphill" to the carburetor/spacer, so as to permit oil condensate in these lines to hopefully drain back to the valve cover.

But, even then, one can envision the scenario were as descending down a long grade that the engine cylinders will cool, as the R.P.M.s are elevated against a reduced or even closed throttle (greatly reducing cylinder pressure), compounded by a maybe less than ideal state of tune (carburetor to lean or more likely an overly rich mixture) situation, thereby causing inadequate combustion sufficient to burn the oil vapor drawn in thru an even properly operating P.C.V. system.

Well, you asked!:D


06-15-2017, 09:22 AM
Nyles - thanks!
I failed to mention this is a '65 (C5AE) intake with no road draft tube on the back. I did make a similar contraption on my OEM intake though.

Scott - are you saying that my brand new Holley carb is a piece of junk?


Or it could be the guys fault that adjusted it - wonder who that could be?

Probably is running rich - according to the documentation that came with it the carb was "factory set for optimum performance" - ha - made minor adjustments until finally giving up and cranking on the float levels etc until the car would actually run.

Anyway - your scenario sounds very plausible - I climb a steep grade for 20 min or so and the engine temp climbs. Get to the top of the mountain and the outside temp is normally 5-10 deg cooler. A mostly flat ride for another 15-20 min and the engine temp comes back to normal-ish then hit the down hill grade for 15-20 min and the engine temp drops - this is when I start smelling the burning oil.

As you and Dave mention - no baffle that I'm sure contributes to the problem.

Thinking back though - I didn't replace the PCV valve after the engine fire so the PCV valve could be damaged. Will try that easy fix first (that won't be it). Could always stick an ugly set of valve covers on there with a baffle and give it a shot. I would just hate to get the Tbird out on a nice sunny day like today and try it - :rolleyes:

Might try and tack-weld a small baffle to the PCV valve and hope that would not damage it. Sounds easier than installing some type of home made baffle on the valve train (I like those chrome covers and want to keep them) but will cross that bridge another day.

Thanks again for the comments and ideas guys.


06-15-2017, 11:39 AM
I believe Holley markets a fine product, and as far as carburetors go I prefer them to most others, for ease of tunability and producing best performance.

Now, whether or not the specific unit you received is maybe, defective, well, such does happen with any product at times, unfortunately.

As far as being optimally tuned out-of-the-box?, I never have prescribed to such malarkey, and always advise customers that the carburetor (whatever manufacturer) will require "some" tuning effort to be optimum/ideal for the specific application one chooses to apply it to. The unit is somewhat "universal" in their intended application, therefore one may need to "taylor" it some for best performance, and failing to put forth such effort generally means one will reap less than ideal results.

One of the advantages to the Holley product is that it is relatively simple design (engineered in time when things were intended to be such), and straightforward in it's cause-and-effect systems, allowing the tuner to isolate concerns and address the specific system at fault.

And I always advise that this is an excellent opportunity for the owner-operator to become involved with one's hobby, educate one's self on the product (it's really not that complicated), modifications/tuning proves to be mostly trial-and-error as one attempts to draw a conclusion, and as best results are always realized in this scenario.

Don't be intimidated, think about it, dive-in, and remember - we're-havin'-fun, right!


06-15-2017, 02:16 PM
I'm with pbf777 regarding Holleys.
I've used several and found them a straightforward easy to adjust carb - having said that, I shy away from the 'economy/poverty' models with the non-adjustable floats.
The one on the 429 in my '55 F100 is one I bought in '78 and so far a pin-hole in a float has been the only problem I've had with it.

If anybody is unsure about their Holley there's a Peterson type book all about them.

06-15-2017, 03:30 PM
Reading the thread, it sounds like you're fighting 2 separate problems.
Holley running rich and sucking oil through the PCV system.
As for the Holley running rich, many years back I kept having problems with mine running rich. What I found was the main body gasket between the valve body and main body would go bad, and when that happened it would loose vacuum to the power valve and started dumping fuel like crazy. I'd change the gaskets and I was good for a year. I thought Holley had changed gasket material and hopefully got rid of that problem, but who knows. They're easy gaskets to change. When I couldn't lean it out with the idle screws, I knew it was time to change the gaskets.

Ladysmith Bob
06-18-2017, 11:08 PM
An old style cure.

06-19-2017, 12:30 AM
I love it, Bob. This device reminds me of a coalescing air filter. Painters rely on them to extract water from their air supply. In this case we're extracting oil solids from blowby gasses.

The grocery store sells stainless steel pot scrubbers. They aren't sharp, they don't shed and they don't rust. I was thinking of using one of those, shoved down the oil filler tube. The non-vented push-on cap simply holds a rubber grommet for a PCV valve.

Really, all we want it to do is catch liquid oil and send it back down to the oil pan. Those pot scrubbers are coarse enough to allow fresh oil to pass (albeit slowly) when the oil is changed. Or, the curly-metal scrubber can be pulled out and washed, then re-inserted. Under normal use, gasses can pass right through.

PCV valve rubber grommets are sold everywhere. They require a 1-1/4" outside hole. The inside diameter is typically 1" for the valve. It's just a thought... - Dave

Joe Johnston
06-19-2017, 07:57 AM
lots of guys with GM V-6's are using a similar "catch can" to keep oil from contaminating the mas air flow sensors in the intake air passage. GM just used a recess in the plastic to hold any condensed oil.

The Stainless scrubber is what I used in the valley pan of my Y-Block many years ago and still is as good as ever. Stainless does not deteriorate in that environment and is better than original steel.