Hey why is the driver side valve cover ported to the manifold vacuum? This looks like this is how the stock set up was on my 318 but not sure. Why is this needed?
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Vacuum questions 318 Edlebrock Performer and Demon 1900 set up
- Thread starter Moparfiend
- Start date
Is this to help vent the driver side valve train? Can I just vent this via a large port that I will have with my new valve covers?
BTW I just ordered these which has a large hole on both sides for filling and venting and an additional one that can be punched out (size?)
Crankcase ventilation would be my guess without seeing a pic.
J. Cower
Well-Known Member
On my 318, the valve cover part you're pointing to is the pcv valve and this runs to the back of the carb. The other part in your bottom pic is where the brake booster check valve hose goes.
Thanks J. Mine was not connected when I got the car so it was an assumption. What you described makes more sense. The bottom pic is probably manifold vacuum which is what we need for the power assist brakes.
The top pic is what is still confounding me. The carb connection you speak if must be also manifold vacuum. Then why vent to the vacuum other than to be more efficient to vacuum out more air from a small diameter hose to releave pressure? I believe this is why. Crankcase ventilation adequacy is often not well understood at least by me..... Can Anyone else help explain this?
The top pic is what is still confounding me. The carb connection you speak if must be also manifold vacuum. Then why vent to the vacuum other than to be more efficient to vacuum out more air from a small diameter hose to releave pressure? I believe this is why. Crankcase ventilation adequacy is often not well understood at least by me..... Can Anyone else help explain this?
You get blow by in your motor and without pulling the gas out is can make seals weep. That is all I know that can happen by not having a pcv system in place. They did do it for emissions as well to re burn that blow by gas. The big nipple on the intake looks to go to the brake booster? Small is vacuum accessory.
On my two motors (318 and 440) the pcv hose goes to the front of the carb. The rear has a port for power brakes. Both have Edelbrocks.
On my two motors (318 and 440) the pcv hose goes to the front of the carb. The rear has a port for power brakes. Both have Edelbrocks.
Threewood that makes sense from what I have read and have experienced on my Chevy’s in the past as they were hooked up similarly.
I suppose the real question is can a large breather work sufficiently to maintain the right gas presures?
RRtor another way of asking is does Positive Cranke Case Pressure require a vacuum draw to maintain the corect vent pressure.
I will asert that a larger enough vent to the atmosphere should be just fine but would not meet the environmental purpose that the original design.
My concern is twofold. First unburnt hydrocarbons will creat a variable in the AF mix. I have had a lot of detonation issues on engines and a good AF mix is critical. I don’t expect it to be an issue on a relaxed 318 but like all else my luck just sucks. I also plan on raising the compression on the motor later.
Second the gas contamination is probably not that great to mix and will probably create build up at an accelerated rate.
I suppose the real question is can a large breather work sufficiently to maintain the right gas presures?
RRtor another way of asking is does Positive Cranke Case Pressure require a vacuum draw to maintain the corect vent pressure.
I will asert that a larger enough vent to the atmosphere should be just fine but would not meet the environmental purpose that the original design.
My concern is twofold. First unburnt hydrocarbons will creat a variable in the AF mix. I have had a lot of detonation issues on engines and a good AF mix is critical. I don’t expect it to be an issue on a relaxed 318 but like all else my luck just sucks. I also plan on raising the compression on the motor later.
Second the gas contamination is probably not that great to mix and will probably create build up at an accelerated rate.
747mopar
Well-Known Member
I wouldn't do it, it's always best to have a breather on one valve cover and a pcv on the other hooked to the back of the carb. Without it you'll be more prone to leaks. Racers wanting to eliminate contamination still realize the importance of positive crankcase ventilation and use the headers as a way of accomplishing it, bungs welded at the right angle have a scavenging affect creating a draw and serve the purpose but burn it in the pipes instead of the motor.
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Even in the early 60's, before pcv valves, they knew it was an issue. My 62 had a long vent tube that dropped below the k frame and had a fin attached to create a vacuum in the tube while driving.
Strange lol
You're telling me. But, I was getting leaks with that system so I converted to a pcv setup and the motor has remained relatively dry.
Steve Garner
Well-Known Member
In addition to maintaining crankcase pressure the pcv ensures a flow of clean filtered air through the crankcase to get rid of water and chemical vapour. That's why it's important that in addition to your pcv valve you have a filtered breather for replacement air. I personally don't like the cap type in the valve cover. The filter is fine enough to keep birds out, but they're usually just stuffed with a steel wool type material. The later OE took air from the bottom of the air cleaner housing after it's been through the nice paper filter.
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