Retro-fit PCV Valve

[Lucky Penny]

I have a 1977 Mercruiser (Chevy) 350 (5.7L) engine with a Q-Jet. The current configuration is with two hoses coming off of the valve cover and venting into the Flame Arrester. My intake manafold has a plugged port about mid way between the carb and flywheel cover.
Now for the question. is it possible to retro fit a PCV valve on this engine using the intake maniflold access and connect the hoses to a 'T' then into the PCV valve, or does the PCV have to take its vac source off the carb.

Ok that is enough for now.

 

[Haut Medoc]

Re: Retro-fit PCV Valve

There is no PCV & no need for one......​

 

[Bondo]

Re: Retro-fit PCV Valve

Ayuh,...... 1 Question LP,.......... WHY,..??

It's worked the way it is for 31 Years,........

 

[Haut Medoc]

Re: Retro-fit PCV Valve

Ayuh,...... 1 Question LP,.......... WHY,..??

It's worked the way it is for 31 Years,........

Hah, beat ya that time.....

 

[Bondo]

Re: Retro-fit PCV Valve

Ayuh,.....

Probably because You're in so much Better Shape, from Shoveling all that Snow.......

We've been out Sunbathing for a Week.....
Put the Tugboat in last weekend,.... Hopefully the Houseboat,+ the Sunkhaze Maineiac will launch This weekend.......

 

[Lucky Penny]

Re: Retro-fit PCV Valve

Ayuh,...... 1 Question LP,.......... WHY,..??

It's worked the way it is for 31 Years,........

Because 31 years ago PCV Valves were only available on less than 50% of all engines. But the main reason for my question is would it not be more efficent to draw blow back into the manifold burn it off, and safer not having to worry about clean the flame arrester of the oil resedue.

Besides, I am old and any answer that begins with "because we/I have always done it that way......" is just not an answer. wouldn't it be so much easier to say, "that is the design of the engine" That I can accept.

Thank you anyway.

 

[WizeOne]

Re: Retro-fit PCV Valve

Because 31 years ago PCV Valves were only available on less than 50% of all engines. But the main reason for my question is would it not be more efficent to draw blow back into the manifold burn it off, and safer not having to worry about clean the flame arrester of the oil resedue.

Besides, I am old and any answer that begins with "because we/I have always done it that way......" is just not an answer. wouldn't it be so much easier to say, "that is the design of the engine" That I can accept.

Thank you anyway.

The answer to your question is Yes, you can use the vacuum manifold source. On motors that came equiped with PCV's they often took the vacuum from a spacer port at the base of the carb.

....and yes, it would eliminate the oil on your flame arrestor.

I make no claims as to the veracity of using the PCV vs what basically amounts to the old road draft method, but I do have a mechanic friend who was appalled that his newly aquired, late 70's marine 305 did not have one. He installed one and used the manifold vacumm port.

 

[mkast]

Re: Retro-fit PCV Valve

An auto style PCV has a spring inside of it. Crankcase pressure has to overcome the spring pressure to open the valve. In marine use, NO SPRING. It's just an empty shell, used to attach a hose to. In a marine use there isn't crankcase pressure to over come a spring, just flowing crankcase vapor. So let's complicate the installation by adding unnecessary parts the manufacturer didn't think was needed.
You didn't mention what area your engineering degree is in?

 

[WizeOne]

Re: Retro-fit PCV Valve

A quote from JalopyJournal.com

"Do you absolutely need a PCV system? No. If you are tired of the oily film on the engine and firewall or you don?t want sludge build up inside the engine, then one is recommended."

Like I said the crankcase being vented to the outside surface of the flame arrestor is nothing but a modified road draft system and a poor one at that. With a real road draft crankcase vent system vacuum was created on the tip of the road draft tube, when the car was in motion, literally sucking the blowby gases out of the crank case. When an early car (pre PCV valve) was at idle, depending on the degree of blowby, you could actually see oil vapor rising out of the oil filler breather.

I really doubt that the crankcase vented to the outside edge of the flame arrestor creates near the suction in the vent tube that the road draft tube did, even when you are running at WOT.

I have in my greazzy hand a Motocraft EV50 PCV valve. It came stock on my Ford 302 marine engine. You can google it. It was a part commonly used on 70's era Ford Automobiles as well.

It has a check valve but it is not spring loaded. It simply opens and closes based on the manifold engine vacuum which provides positive suction at times of high engine vacuum and sucks the oily vapor back into the combustion chamber instead of spewing it all over the outside of the engine and or flame arrestor.

 

[Bt Doctur]

Re: Retro-fit PCV Valve

Marine engines usually run very close to their WOT. With the throttle plates wide open there is no manifold vac.to speak of.

 

[WizeOne]

Re: Retro-fit PCV Valve

Marine engines usually run very close to their WOT. With the throttle plates wide open there is no manifold vac.to speak of.

While it is true that your engine develops virtually no vacuum at full WOT or at any other state of acceleration, I would venture to say that not many run constantly at full WOT. At any other position of constant throttle, short of full WOT and at times of any deceleration, you would have sufficient vacuum to operate the PCV valve.

It is true that for those relatively short periods of acceleration or full WOT, your normal oil filler breather takes up the slack. All a far cry from crankcase gases lazily winding it's way up a 1/2" hose to terminate at a position of virtually nil suction. (outside edge of 360 degree flame/spark arrestor)

 

[rodbolt]

Re: Retro-fit PCV Valve

most modern MPI motors use a PCV valve simply to aid in emissions standards, most hulls at planing speed are under considerable load and intake vacum is very low so most PCV valves are useless.
merc,OMC volvo and a host of others never used a PCV valve, a few did like PCM. you can try it, buy one for the 5.7 MPI volvo worst that can happen is you lean out that cylinder and burn a valve, if it runs funny after installation simply uninstall it, its not microsoft

 

[Bondo]

Re: Retro-fit PCV Valve

Ayuh,............

Just make darn sure it's Marine Rated.........................

 

[bomar76]

Re: Retro-fit PCV Valve

This whole idea goes under "Solutions to problems that don't exist"..that are likely to create a disater...

 

[Mkos1980]

Re: Retro-fit PCV Valve

If I am thinking about the plug your talking about, isnt that the one in the number 8 runner? If so dont use that one.