Dangerous Vacuum?
Thread Starter
Instructor
Joined: Dec 2007
Posts: 245
Likes: 2
From: Jersey shore NJ
Dangerous Vacuum?
I'm trying to hook up my vacuum accessories to my new carb and I see a few other threads that are trying to do the same thing.
My new carb only has one 3/8" vacuum port on the back for power brakes. On Lar's paper on how to set up a demon carb, he uses a " T " fitting to run the power brakes and PVC to the back of the carb. I was going to do this ,then someone told me I could cause a problem with the brakes having the pvc on the same line as the brake booster. Has anyone set up their vacuum lines this way?? and did it cause any issues with the brakes?
My new carb only has one 3/8" vacuum port on the back for power brakes. On Lar's paper on how to set up a demon carb, he uses a " T " fitting to run the power brakes and PVC to the back of the carb. I was going to do this ,then someone told me I could cause a problem with the brakes having the pvc on the same line as the brake booster. Has anyone set up their vacuum lines this way?? and did it cause any issues with the brakes?
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
I'm trying to hook up my vacuum accessories to my new carb and I see a few other threads that are trying to do the same thing.
My new carb only has one 3/8" vacuum port on the back for power brakes. On Lar's paper on how to set up a demon carb, he uses a " T " fitting to run the power brakes and PVC to the back of the carb. I was going to do this ,then someone told me I could cause a problem with the brakes having the pvc on the same line as the brake booster. Has anyone set up their vacuum lines this way?? and did it cause any issues with the brakes?
My new carb only has one 3/8" vacuum port on the back for power brakes. On Lar's paper on how to set up a demon carb, he uses a " T " fitting to run the power brakes and PVC to the back of the carb. I was going to do this ,then someone told me I could cause a problem with the brakes having the pvc on the same line as the brake booster. Has anyone set up their vacuum lines this way?? and did it cause any issues with the brakes?
Le Mans Master
Joined: Jan 2006
Posts: 6,506
Likes: 139
From: Butler Pa
I know, a lot of people do, but personally, I wouldn't hook it up that way. A PCV valve is essentially a constant, though restricted vacuum leak. It could, depending on how it's plumbed and what fittings are used, decrease the vacuum signal to the booster. Also, PCV valves do occasionally fail. That's why you can go just about anywhere and buy one. In the event of a failure, the vacuum signal could be greatly reduced.
I suppose there's also the possibility of engine oil entering the booster. Not sure what effect this may have.
I suppose there's also the possibility of engine oil entering the booster. Not sure what effect this may have.
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
I know, a lot of people do, but personally, I wouldn't hook it up that way. A PCV valve is essentially a constant, though restricted vacuum leak. It could, depending on how it's plumbed and what fittings are used, decrease the vacuum signal to the booster. Also, PCV valves do occasionally fail. That's why you can go just about anywhere and buy one. In the event of a failure, the vacuum signal could be greatly reduced.
I suppose there's also the possibility of engine oil entering the booster. Not sure what effect this may have.
I suppose there's also the possibility of engine oil entering the booster. Not sure what effect this may have.
.....a faulty pcv would have the same effect on the vacuum signal no matter where it is hooked up to a direct manifold port, albeit the manifold fittings or the carb base....truth....
Last edited by midyearvette; Mar 25, 2009 at 08:44 AM.
Le Mans Master
Joined: Jan 2006
Posts: 6,506
Likes: 139
From: Butler Pa
That's true if you're talking about the vacuum signal inside the manifold. The problem is you now have 2 systems using vacuum through 1 port which was designed to supply vacuum to only 1 system. A tee causes an even bigger restriction. Why do you think GM never did this?
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
That's true if you're talking about the vacuum signal inside the manifold. The problem is you now have 2 systems using vacuum through 1 port which was designed to supply vacuum to only 1 system. A tee causes an even bigger restriction. Why do you think GM never did this?
Last edited by midyearvette; Mar 25, 2009 at 09:33 AM.
Le Mans Master
Joined: Jan 2006
Posts: 6,506
Likes: 139
From: Butler Pa
It's very simple to drill a new port. I've done it several times.
Determine where you want the new port. Remove carb and make sure you'll have sufficient wall thickness.
Take the hose from your shop vac/vacuum cleaner and stick it inside the manifold next to where you'll be drilling the hole.
Drill and tap. Replace carb.
Determine where you want the new port. Remove carb and make sure you'll have sufficient wall thickness.
Take the hose from your shop vac/vacuum cleaner and stick it inside the manifold next to where you'll be drilling the hole.
Drill and tap. Replace carb.
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Thread Starter
Instructor
Joined: Dec 2007
Posts: 245
Likes: 2
From: Jersey shore NJ
Victoriavette, the papers for this are on Barryks web site.
I was going to drill and tap the intake, but I only found fittings with pipe threads. Can you use a standard tap with pipe fittings that are tapered??
I was going to drill and tap the intake, but I only found fittings with pipe threads. Can you use a standard tap with pipe fittings that are tapered??
Drifting
Joined: Apr 2007
Posts: 1,970
Likes: 45
From: Cameron Park CA
Cheers,
Pete
Thread Starter
Instructor
Joined: Dec 2007
Posts: 245
Likes: 2
From: Jersey shore NJ
Thanks Pete, I will look for the pipe tap.
How much vauum does the PVC need? My new drop base air cleaner has a fitting that you can put on the bottom for a 3/8" hose. Can the PVC be hooked up to the bottom of the air cleaner? My original air cleaner had the fitting on the air cleaner going to the valve cover for the breather.
How much vauum does the PVC need? My new drop base air cleaner has a fitting that you can put on the bottom for a 3/8" hose. Can the PVC be hooked up to the bottom of the air cleaner? My original air cleaner had the fitting on the air cleaner going to the valve cover for the breather.