Switching to PCV valve?

[denpo]

While reconnecting the vacuum gas plan, I learned a bit about valve cover PCV and breather.
I have breathers (old pic, but valve cover still the same).



I'm thinking about putting PCV valve instead.

Is it a good idea?
Can it be source on the cheap (scrapyard)?
Do I need to look for a specific model to fit my fancy covers?

 

[mrvette]

My only comment about PCV, which is a GOOD thing is that it has to be taken off a baffled region in the lifter valley, anything off a valve cover is crap....

it just impedes oil drain back to much ......

Olde tyme Pontiac man here, and the old Ponchos had the PCV done off the lifter valley pan cover, separate piece from the typical Chebby install.... and so never an issue with oil seeping/weeping issues,

but on all the SBC engines I know of there always was a PCV issue from the valve cover location....

UNTIL I got a LT1 intake modified to fit my L98 engine, and that induction had the same essential location with baffle plate under it....that the olde tyme Pontiac engine had.....and I have NO troubles with oiling problems over the valve covers NOW....


Case A compared to B......tells me that PCV valves don't belong in the valve covers....lifter valley is much better.....:1st::beer:

 

[Belgian1979vette]

Not all PCV's are the same. A carb is usually made to use PCV. If the cam is agressive enough it may need the additional airflow. It will let you close the throttles more so that you have proper transferslot exposure.

Additionally when the engine is warm, it will suck vapors and more importantly any condens out of the engine. You do not have that with just a breather.

However...the valve must not allow too much air at high vacuum. Therefor it kinda needs to be tuned to your application. Factory PCV's are great, but mostly they don't fit the aftermarket valvecover holes.

 

[denpo]

Not all PCV's are the same. A carb is usually made to use PCV. If the cam is agressive enough it may need the additional airflow. It will let you close the throttles more so that you have proper transferslot exposure.

Additionally when the engine is warm, it will suck vapors and more importantly any condens out of the engine. You do not have that with just a breather.

However...the valve must not allow too much air at high vacuum. Therefor it kinda needs to be tuned to your application. Factory PCV's are great, but mostly they don't fit the aftermarket valvecover holes.

Do you have a "for dummies" version of the highlighted part? :huh::tomato:

Note:
My carb: Holley 4150, probably 750cfm.
My cam: COMP Cams 12-678-4 Camshaft, Mechanical Flat Tappet, Duration 282/290, Lift .520/.540

 

[Twin_Turbo]

the carb gets leaked PCV air in and this raises the idle speed, which allows you to close the throttle blades further to get the idle speed down, this helps keep the blades in an idle pos. so the transfer slot is not fully exposed to manifold vacuum that exists under the throttle blades when closed.

These PCV valves fit the large opening of a breather:

http://www.summitracing.com/parts/ear-3434116erl

 

[denpo]

the carb gets leaked PCV air in and this raises the idle speed, which allows you to close the throttle blades further to get the idle speed down, this helps keep the blades in an idle pos. so the transfer slot is not fully exposed to manifold vacuum that exists under the throttle blades when closed.

These PCV valves fit the large opening of a breather:

http://www.summitracing.com/parts/ear-3434116erl

Thanks TT, I get it.
Learned a new thing today (carb transfert slot).

 

[MYBAD79]

another thing to consider is crankcase pressure - if you vent both valve covers to atmosphere without a vacuum line anywhere there's a good chance you'll have oil puking out of the breathers. Connecting the suction line to one of the valve covers is usually good enough but connecting it to a port on the manifold like Gene says is not a bad idea either, might have to drill and tap for NPT but its a cleaner solution IMO than the valve cover.
Best way to say it is maybe this: you want "air in" instead of "oil out" so you want the crankcase connected to the vacuum port of the carb..... I just made this mistake when I added a breather to my aircooled VW engine, I completely forgot (overlooked) that I needed a suction line .... that would have ended in a nasty oil spray

 

[SuperBuickGuy]

Not all PCV's are the same. A carb is usually made to use PCV. If the cam is agressive enough it may need the additional airflow. It will let you close the throttles more so that you have proper transferslot exposure.

Additionally when the engine is warm, it will suck vapors and more importantly any condens out of the engine. You do not have that with just a breather.

However...the valve must not allow too much air at high vacuum. Therefor it kinda needs to be tuned to your application. Factory PCV's are great, but mostly they don't fit the aftermarket valvecover holes.

Do you have a "for dummies" version of the highlighted part? :huh::tomato:

Note:
My carb: Holley 4150, probably 750cfm.
My cam: COMP Cams 12-678-4 Camshaft, Mechanical Flat Tappet, Duration 282/290, Lift .520/.540

ummmm.... do you really think you have enough vacuum from the motor to make the PCV work? My cam is slightly less radical and there's just not enough vacuum to make a pcv valve anything other than a vacuum leak

 

[Belgian1979vette]

the carb gets leaked PCV air in and this raises the idle speed, which allows you to close the throttle blades further to get the idle speed down, this helps keep the blades in an idle pos. so the transfer slot is not fully exposed to manifold vacuum that exists under the throttle blades when closed.

These PCV valves fit the large opening of a breather:

http://www.summitracing.com/parts/ear-3434116erl

Thanks TT, I get it.
Learned a new thing today (carb transfert slot).

TT explained it perfect. Sorry, I used to much technical terms. You're looking for around .20-.030 transfer slot exposure. Take the carb off, turn it upside down and andjust curb idle for correct exposure. Make sure your secondaries are set correctly (1/4th open from closed position). Set it back on, start it and see what it does. If it doesn't want to run when cold, open the curb idle screw untill you have it running, closing it again when it goes up in rpm when warming up, each time counting the amount of turns it took. Hook up PCV and see what it does trying to close the throttle plates to the original setting. If you cannot get there, take the carb off again and open the secondaries 1/2 turn more. Go over it again untill you have equilized things. Try getting a AFR in the 13 range.

A 750 DP ? 4 corner idle (I assume not seeing the choke tower)? If not and you intend to run a carb get one, it will make idle setting better. (What LCA on the cam because that determines your vacuum ?)

 

[Belgian1979vette]

Not all PCV's are the same. A carb is usually made to use PCV. If the cam is agressive enough it may need the additional airflow. It will let you close the throttles more so that you have proper transferslot exposure.

Additionally when the engine is warm, it will suck vapors and more importantly any condens out of the engine. You do not have that with just a breather.

However...the valve must not allow too much air at high vacuum. Therefor it kinda needs to be tuned to your application. Factory PCV's are great, but mostly they don't fit the aftermarket valvecover holes.

Do you have a "for dummies" version of the highlighted part? :huh::tomato:

Note:
My carb: Holley 4150, probably 750cfm.
My cam: COMP Cams 12-678-4 Camshaft, Mechanical Flat Tappet, Duration 282/290, Lift .520/.540

ummmm.... do you really think you have enough vacuum from the motor to make the PCV work? My cam is slightly less radical and there's just not enough vacuum to make a pcv valve anything other than a vacuum leak

That's the problem. A PCV should be tuned to work under high vacuum conditions. Meaning, closing it off more if more vacuum exists. If of course your engine idles at 6 " of vacuum like mine, the PCV will be open all the time. This will let to much additional air in, leaning out AFR at idle. Only problem I have now is that my idle feed restriction is too small and I have to turn the idle screw out too much.
A 4 corner idle would have been better in this situation, but I'm only intending to use it for the first 500 km and then I'm converting over to efi anyway.

Maybe there is a way to tune the PCV to a specific combination, but in my case it's too much hassle for only 500 km before converting to efi.

 

[Belgian1979vette]

Denpo,

Something else : get your initial ignition timing set correctly. Large cams need a lot of ignition advance at idle, especially when running a single plane manifold.
When setting it, get it to about 18° initial and see what it does. The more the better, but you have to make sure you the motor doesn't start lugging or you cannot start her when hot. Make sure you run your starter brace.
I have a 300° mech roller (advertised) with a victor jr and it needs 26 initial. Had to get a special bushing to get there. Lots of reversion and some misfires.

Don't forget to re-adjust your centrifugal advance so you have a 34-36 maximum at around 2500-3000 rpm !!!! Limit your vacuum advance to 10-12° (46-48 all in)

My bet is you'll have issues getting it to idle correctly. Might even need a higher idle rpm like 1100 or so.

 

[Twin_Turbo]

Crank retard

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[Belgian1979vette]

Crank retard

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I know, but pretty expensive. When all is said and done (new carb, ignition retard, new dizzy with adjustable advance curves) he's close to converting over to an EFI and then you don't need it anymore as you can program an ignition retard into the tables.

Some of those, like the ones from MSD keep retarding it untill 1300 rpm, making it useless in my opinion as you need a huge amount of timing at idle, only not when the starter motor is running (like 300 rpm or so)

 

[denpo]

Not all PCV's are the same. A carb is usually made to use PCV. If the cam is agressive enough it may need the additional airflow. It will let you close the throttles more so that you have proper transferslot exposure.

Additionally when the engine is warm, it will suck vapors and more importantly any condens out of the engine. You do not have that with just a breather.

However...the valve must not allow too much air at high vacuum. Therefor it kinda needs to be tuned to your application. Factory PCV's are great, but mostly they don't fit the aftermarket valvecover holes.

Do you have a "for dummies" version of the highlighted part? :huh::tomato:

Note:
My carb: Holley 4150, probably 750cfm.
My cam: COMP Cams 12-678-4 Camshaft, Mechanical Flat Tappet, Duration 282/290, Lift .520/.540

ummmm.... do you really think you have enough vacuum from the motor to make the PCV work? My cam is slightly less radical and there's just not enough vacuum to make a pcv valve anything other than a vacuum leak

That's the problem. A PCV should be tuned to work under high vacuum conditions. Meaning, closing it off more if more vacuum exists. If of course your engine idles at 6 " of vacuum like mine, the PCV will be open all the time. This will let to much additional air in, leaning out AFR at idle. Only problem I have now is that my idle feed restriction is too small and I have to turn the idle screw out too much.
A 4 corner idle would have been better in this situation, but I'm only intending to use it for the first 500 km and then I'm converting over to efi anyway.

Maybe there is a way to tune the PCV to a specific combination, but in my case it's too much hassle for only 500 km before converting to efi.

At low RPM I had to stand on the pedal brake to get it to a stop, I pretty sure the vacuum is very weak, that's why I opted for a HB.

I added a manual choke because the car didn't hold idle when cold.
When warm it was good.
The Holley is vacuum secondary, and the vacuum port wasn't even hooked to the distributor.....:amazed:
PO told me he tried to change the secondary spring and didn't see any change in engine behaviour, I think I see why.:suspicious:
Of course PO stopped communicating once the car sold, he knew that everything but the engine was a POS.:hunter:

All this make me think I should first try to run the engine again, have the current AFR and vacuum measured and see where to go from that.
Getting the car tuned/dyno'ed is in the todo list anyway.
I thought is would be a quick fix, boy I was wrong.
Thanks for all the advice.
:drink:Chimay for everyone!

 

[kwplot34]

This is the cam specs on my solid roller cam. Pretty aggressive cam. And my brakes work just fine.


Here is a cure to the PCV. Front left on the motor connected to the valve cover by that big black hose.

 

[Belgian1979vette]

Not all PCV's are the same. A carb is usually made to use PCV. If the cam is agressive enough it may need the additional airflow. It will let you close the throttles more so that you have proper transferslot exposure.

Additionally when the engine is warm, it will suck vapors and more importantly any condens out of the engine. You do not have that with just a breather.

However...the valve must not allow too much air at high vacuum. Therefor it kinda needs to be tuned to your application. Factory PCV's are great, but mostly they don't fit the aftermarket valvecover holes.

Do you have a "for dummies" version of the highlighted part? :huh::tomato:

Note:
My carb: Holley 4150, probably 750cfm.
My cam: COMP Cams 12-678-4 Camshaft, Mechanical Flat Tappet, Duration 282/290, Lift .520/.540

ummmm.... do you really think you have enough vacuum from the motor to make the PCV work? My cam is slightly less radical and there's just not enough vacuum to make a pcv valve anything other than a vacuum leak

That's the problem. A PCV should be tuned to work under high vacuum conditions. Meaning, closing it off more if more vacuum exists. If of course your engine idles at 6 " of vacuum like mine, the PCV will be open all the time. This will let to much additional air in, leaning out AFR at idle. Only problem I have now is that my idle feed restriction is too small and I have to turn the idle screw out too much.
A 4 corner idle would have been better in this situation, but I'm only intending to use it for the first 500 km and then I'm converting over to efi anyway.

Maybe there is a way to tune the PCV to a specific combination, but in my case it's too much hassle for only 500 km before converting to efi.

At low RPM I had to stand on the pedal brake to get it to a stop, I pretty sure the vacuum is very weak, that's why I opted for a HB.

I added a manual choke because the car didn't hold idle when cold.
When warm it was good.
The Holley is vacuum secondary, and the vacuum port wasn't even hooked to the distributor.....:amazed:
PO told me he tried to change the secondary spring and didn't see any change in engine behaviour, I think I see why.:suspicious:
Of course PO stopped communicating once the car sold, he knew that everything but the engine was a POS.:hunter:

All this make me think I should first try to run the engine again, have the current AFR and vacuum measured and see where to go from that.
Getting the car tuned/dyno'ed is in the todo list anyway.
I thought is would be a quick fix, boy I was wrong.
Thanks for all the advice.
:drink:Chimay for everyone!

That makes me think something else is going on. Check your ignition.

 

[denpo]

At low RPM I had to stand on the pedal brake to get it to a stop, I pretty sure the vacuum is very weak, that's why I opted for a HB.
......

That makes me think something else is going on. Check your ignition.

That can also be that the brake system was crap : rusted lines, old rubber hoses, MC full of gunk, rusted caliper cylinder, leap seals.....
Now SS lines, SS braided hoses, new MC, O-ring. The replacement calipers are still worrying me, but that's another story.....
From now I would probably have waited to jump the HB bangwagon.

 

[denpo]

Here is a cure to the PCV. Front left on the motor connected to the valve cover by that big black hose.

Is that a additionnal vacuum pump?
I see you have it on one side, what's on the other?
So you only need one (assuming both cover can equalize pressure)?
Yup, I'm that newbie :blush:

PS: I love you spark wire loom, I thought nothing would work with this type of cover.
PS(2): very nice/neat engine setup.

 

[Twin_Turbo]

Yes the other side has an adjustable valve. There are factory rebuilt aerospace component pumps on ebay for little money...

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[denpo]

Yes the other side has an adjustable valve. There are factory rebuilt aerospace component pumps on ebay for little money...

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LOL, took me a while to realize "aerospace component" was a brand name, not actual word.
Good deal indeed, thanks for the info.
I guess the ouput of the pump simply ... goes out.